clang

src/ripple/app/tx/impl/Transactor.cpp

@@ -289,8 +289,40 @@ Transactor::calculateBaseFee(ReadView const& view, STTx const& tx)
 
     // Each signer adds one more baseFee to the minimum required fee
     // for the transaction.
-    std::size_t const signerCount =
-        tx.isFieldPresent(sfSigners) ? tx.getFieldArray(sfSigners).size() : 0;
+    std::size_t signerCount = 0;
+    if (tx.isFieldPresent(sfSigners))
+    {
+        // Define recursive lambda to count all leaf signers
+        std::function<std::size_t(STArray const&)> countSigners;
+
+        countSigners = [&](STArray const& signers) -> std::size_t {
+            std::size_t count = 0;
+
+            for (auto const& signer : signers)
+            {
+                if (signer.isFieldPresent(sfSigners))
+                {
+                    // This is a nested signer - recursively count its signers
+                    count += countSigners(signer.getFieldArray(sfSigners));
+                }
+                else
+                {
+                    // This is a leaf signer (one who actually signs)
+                    // Count it only if it has signing fields (not just a
+                    // placeholder)
+                    if (signer.isFieldPresent(sfSigningPubKey) &&
+                        signer.isFieldPresent(sfTxnSignature))
+                    {
+                        count += 1;
+                    }
+                }
+            }
+
+            return count;
+        };
+
+        signerCount = countSigners(tx.getFieldArray(sfSigners));
+    }
 
     XRPAmount hookExecutionFee{0};
     uint64_t burden{1};
@@ -923,157 +955,282 @@ NotTEC
 Transactor::checkMultiSign(PreclaimContext const& ctx)
 {
     auto const id = ctx.tx.getAccountID(sfAccount);
-    // Get mTxnAccountID's SignerList and Quorum.
-    std::shared_ptr<STLedgerEntry const> sleAccountSigners =
-        ctx.view.read(keylet::signers(id));
-    // If the signer list doesn't exist the account is not multi-signing.
-    if (!sleAccountSigners)
-    {
-        JLOG(ctx.j.trace())
-            << "applyTransaction: Invalid: Not a multi-signing account.";
-        return tefNOT_MULTI_SIGNING;
-    }
 
-    // We have plans to support multiple SignerLists in the future.  The
-    // presence and defaulted value of the SignerListID field will enable that.
-    assert(sleAccountSigners->isFieldPresent(sfSignerListID));
-    assert(sleAccountSigners->getFieldU32(sfSignerListID) == 0);
+    // Set max depth based on feature flag
+    bool const allowNested = ctx.view.rules().enabled(featureNestedMultiSign);
+    int const maxDepth = allowNested ? 4 : 1;
 
-    auto accountSigners =
-        SignerEntries::deserialize(*sleAccountSigners, ctx.j, "ledger");
-    if (!accountSigners)
-        return accountSigners.error();
+    // Define recursive lambda for checking signers at any depth
+    // ancestors tracks the signing chain to detect cycles
+    std::function<NotTEC(
+        AccountID const&, STArray const&, int, std::set<AccountID>)>
+        validateSigners;
 
-    // Get the array of transaction signers.
-    STArray const& txSigners(ctx.tx.getFieldArray(sfSigners));
-
-    // Walk the accountSigners performing a variety of checks and see if
-    // the quorum is met.
-
-    // Both the multiSigners and accountSigners are sorted by account.  So
-    // matching multi-signers to account signers should be a simple
-    // linear walk.  *All* signers must be valid or the transaction fails.
-    std::uint32_t weightSum = 0;
-    auto iter = accountSigners->begin();
-    for (auto const& txSigner : txSigners)
-    {
-        AccountID const txSignerAcctID = txSigner.getAccountID(sfAccount);
-
-        // Attempt to match the SignerEntry with a Signer;
-        while (iter->account < txSignerAcctID)
+    validateSigners = [&](AccountID const& acc,
+                          STArray const& signers,
+                          int depth,
+                          std::set<AccountID> ancestors) -> NotTEC {
+        // Cycle detection: if we're already validating this account up the
+        // chain it cannot contribute - but this isn't an error, just
+        // unavailable weight
+        if (ancestors.count(acc))
         {
-            if (++iter == accountSigners->end())
+            JLOG(ctx.j.trace())
+                << "checkMultiSign: Cyclic signer detected: " << acc;
+            return tesSUCCESS;
+        }
+
+        // Check depth limit
+        if (depth > maxDepth)
+        {
+            if (allowNested)
             {
                 JLOG(ctx.j.trace())
-                    << "applyTransaction: Invalid SigningAccount.Account.";
+                    << "checkMultiSign: Multi-signing depth limit exceeded.";
                 return tefBAD_SIGNATURE;
             }
-        }
-        if (iter->account != txSignerAcctID)
-        {
-            // The SigningAccount is not in the SignerEntries.
-            JLOG(ctx.j.trace())
-                << "applyTransaction: Invalid SigningAccount.Account.";
-            return tefBAD_SIGNATURE;
+
+            JLOG(ctx.j.warn())
+                << "checkMultiSign: Nested multisigning disabled.";
+            return temMALFORMED;
         }
 
-        // We found the SigningAccount in the list of valid signers.  Now we
-        // need to compute the accountID that is associated with the signer's
-        // public key.
-        auto const spk = txSigner.getFieldVL(sfSigningPubKey);
+        ancestors.insert(acc);
 
-        if (!publicKeyType(makeSlice(spk)))
+        // Get the SignerList for the account we're validating signers for
+        std::shared_ptr<STLedgerEntry const> sleAllowedSigners =
+            ctx.view.read(keylet::signers(acc));
+
+        if (!sleAllowedSigners)
         {
-            JLOG(ctx.j.trace())
-                << "checkMultiSign: signing public key type is unknown";
-            return tefBAD_SIGNATURE;
+            JLOG(ctx.j.trace()) << "checkMultiSign: Account " << acc
+                                << " not set up for multi-signing.";
+            return tefNOT_MULTI_SIGNING;
         }
 
-        AccountID const signingAcctIDFromPubKey =
-            calcAccountID(PublicKey(makeSlice(spk)));
+        uint32_t const quorum = sleAllowedSigners->getFieldU32(sfSignerQuorum);
+        uint32_t sum{0};
 
-        // Verify that the signingAcctID and the signingAcctIDFromPubKey
-        // belong together.  Here is are the rules:
-        //
-        //   1. "Phantom account": an account that is not in the ledger
-        //      A. If signingAcctID == signingAcctIDFromPubKey and the
-        //         signingAcctID is not in the ledger then we have a phantom
-        //         account.
-        //      B. Phantom accounts are always allowed as multi-signers.
-        //
-        //   2. "Master Key"
-        //      A. signingAcctID == signingAcctIDFromPubKey, and signingAcctID
-        //         is in the ledger.
-        //      B. If the signingAcctID in the ledger does not have the
-        //         asfDisableMaster flag set, then the signature is allowed.
-        //
-        //   3. "Regular Key"
-        //      A. signingAcctID != signingAcctIDFromPubKey, and signingAcctID
-        //         is in the ledger.
-        //      B. If signingAcctIDFromPubKey == signingAcctID.RegularKey (from
-        //         ledger) then the signature is allowed.
-        //
-        // No other signatures are allowed.  (January 2015)
+        auto allowedSigners =
+            SignerEntries::deserialize(*sleAllowedSigners, ctx.j, "ledger");
+        if (!allowedSigners)
+            return allowedSigners.error();
 
-        // In any of these cases we need to know whether the account is in
-        // the ledger.  Determine that now.
-        auto sleTxSignerRoot = ctx.view.read(keylet::account(txSignerAcctID));
-
-        if (signingAcctIDFromPubKey == txSignerAcctID)
+        // Build lookup map for O(1) signer validation and weight retrieval
+        std::map<AccountID, uint16_t> signerWeights;
+        uint32_t totalWeight{0}, cyclicWeight{0};
+        for (auto const& entry : *allowedSigners)
         {
-            // Either Phantom or Master.  Phantoms automatically pass.
-            if (sleTxSignerRoot)
+            signerWeights[entry.account] = entry.weight;
+            totalWeight += entry.weight;
+            if (ancestors.count(entry.account))
+                cyclicWeight += entry.weight;
+        }
+
+        // Walk the signers array, validating each signer
+        // Signers must be in strict ascending order for consensus
+        std::optional<AccountID> prevSigner;
+
+        for (auto const& signerEntry : signers)
+        {
+            AccountID const signer = signerEntry.getAccountID(sfAccount);
+            bool const isNested = signerEntry.isFieldPresent(sfSigners);
+
+            // Enforce strict ascending order (required for consensus)
+            if (prevSigner && signer <= *prevSigner)
             {
-                // Master Key.  Account may not have asfDisableMaster set.
-                std::uint32_t const signerAccountFlags =
-                    sleTxSignerRoot->getFieldU32(sfFlags);
+                JLOG(ctx.j.trace())
+                    << "checkMultiSign: Signers not in strict ascending order: "
+                    << signer << " <= " << *prevSigner;
+                return temMALFORMED;
+            }
+            prevSigner = signer;
 
-                if (signerAccountFlags & lsfDisableMaster)
+            // Skip cyclic signers - they cannot contribute at this level
+            if (ancestors.count(signer))
+            {
+                JLOG(ctx.j.trace())
+                    << "checkMultiSign: Skipping cyclic signer: " << signer;
+                continue;
+            }
+
+            // Lookup signer in authorized set
+            auto const weightIt = signerWeights.find(signer);
+            if (weightIt == signerWeights.end())
+            {
+                JLOG(ctx.j.trace())
+                    << "checkMultiSign: Invalid signer " << signer
+                    << " not in signer list for " << acc;
+                return tefBAD_SIGNATURE;
+            }
+            uint16_t const weight = weightIt->second;
+
+            // Check if this signer has nested signers (delegation)
+            if (isNested)
+            {
+                // This is a nested multi-signer that delegates to sub-signers
+                if (signerEntry.isFieldPresent(sfSigningPubKey) ||
+                    signerEntry.isFieldPresent(sfTxnSignature))
+                {
+                    JLOG(ctx.j.trace()) << "checkMultiSign: Signer " << signer
+                                        << " cannot have both nested signers "
+                                           "and signature fields.";
+                    return tefBAD_SIGNATURE;
+                }
+
+                // Recursively validate the nested signers against signer's
+                // signer list
+                STArray const& nestedSigners =
+                    signerEntry.getFieldArray(sfSigners);
+                NotTEC result = validateSigners(
+                    signer, nestedSigners, depth + 1, ancestors);
+                if (!isTesSuccess(result))
+                    return result;
+
+                // Nested signers met their quorum - add this signer's weight
+                sum += weight;
+
+                JLOG(ctx.j.trace())
+                    << "checkMultiSign: Nested signer " << signer
+                    << " validated, weight=" << weight << ", depth=" << depth
+                    << ", sum=" << sum << "/" << quorum;
+            }
+            else
+            {
+                // This is a leaf signer - validate signature
+                if (!signerEntry.isFieldPresent(sfSigningPubKey) ||
+                    !signerEntry.isFieldPresent(sfTxnSignature))
                 {
                     JLOG(ctx.j.trace())
-                        << "applyTransaction: Signer:Account lsfDisableMaster.";
-                    return tefMASTER_DISABLED;
+                        << "checkMultiSign: Leaf signer " << signer
+                        << " must have SigningPubKey and TxnSignature.";
+                    return tefBAD_SIGNATURE;
                 }
+
+                auto const spk = signerEntry.getFieldVL(sfSigningPubKey);
+
+                if (!publicKeyType(makeSlice(spk)))
+                {
+                    JLOG(ctx.j.trace())
+                        << "checkMultiSign: Unknown public key type for signer "
+                        << signer;
+                    return tefBAD_SIGNATURE;
+                }
+
+                AccountID const signingAcctIDFromPubKey =
+                    calcAccountID(PublicKey(makeSlice(spk)));
+
+                auto sleTxSignerRoot = ctx.view.read(keylet::account(signer));
+
+                if (signingAcctIDFromPubKey == signer)
+                {
+                    if (sleTxSignerRoot)
+                    {
+                        std::uint32_t const signerAccountFlags =
+                            sleTxSignerRoot->getFieldU32(sfFlags);
+
+                        if (signerAccountFlags & lsfDisableMaster)
+                        {
+                            JLOG(ctx.j.trace())
+                                << "checkMultiSign: Signer " << signer
+                                << " has lsfDisableMaster set.";
+                            return tefMASTER_DISABLED;
+                        }
+                    }
+                }
+                else
+                {
+                    if (!sleTxSignerRoot)
+                    {
+                        JLOG(ctx.j.trace())
+                            << "checkMultiSign: Non-phantom signer " << signer
+                            << " lacks account root.";
+                        return tefBAD_SIGNATURE;
+                    }
+
+                    if (!sleTxSignerRoot->isFieldPresent(sfRegularKey))
+                    {
+                        JLOG(ctx.j.trace()) << "checkMultiSign: Signer "
+                                            << signer << " lacks RegularKey.";
+                        return tefBAD_SIGNATURE;
+                    }
+                    if (signingAcctIDFromPubKey !=
+                        sleTxSignerRoot->getAccountID(sfRegularKey))
+                    {
+                        JLOG(ctx.j.trace())
+                            << "checkMultiSign: Signer " << signer
+                            << " pubkey doesn't match RegularKey.";
+                        return tefBAD_SIGNATURE;
+                    }
+                }
+
+                // Valid leaf signer - add their weight
+                sum += weight;
+
+                JLOG(ctx.j.trace())
+                    << "checkMultiSign: Leaf signer " << signer
+                    << " validated, weight=" << weight << ", depth=" << depth
+                    << ", sum=" << sum << "/" << quorum;
             }
         }
-        else
+
+        // Calculate effective quorum, relaxing for cyclic lockout scenarios
+        // Sanity check: cyclicWeight must not exceed totalWeight (underflow
+        // guard)
+        if (cyclicWeight > totalWeight)
         {
-            // May be a Regular Key.  Let's find out.
-            // Public key must hash to the account's regular key.
-            if (!sleTxSignerRoot)
-            {
-                JLOG(ctx.j.trace()) << "applyTransaction: Non-phantom signer "
-                                       "lacks account root.";
-                return tefBAD_SIGNATURE;
-            }
-
-            if (!sleTxSignerRoot->isFieldPresent(sfRegularKey))
-            {
-                JLOG(ctx.j.trace())
-                    << "applyTransaction: Account lacks RegularKey.";
-                return tefBAD_SIGNATURE;
-            }
-            if (signingAcctIDFromPubKey !=
-                sleTxSignerRoot->getAccountID(sfRegularKey))
-            {
-                JLOG(ctx.j.trace())
-                    << "applyTransaction: Account doesn't match RegularKey.";
-                return tefBAD_SIGNATURE;
-            }
+            JLOG(ctx.j.error()) << "checkMultiSign: Invariant violation for "
+                                << acc << ": cyclicWeight (" << cyclicWeight
+                                << ") > totalWeight (" << totalWeight << ")";
+            return tefINTERNAL;
         }
-        // The signer is legitimate.  Add their weight toward the quorum.
-        weightSum += iter->weight;
-    }
 
-    // Cannot perform transaction if quorum is not met.
-    if (weightSum < sleAccountSigners->getFieldU32(sfSignerQuorum))
+        uint32_t effectiveQuorum = quorum;
+        uint32_t const maxAchievable = totalWeight - cyclicWeight;
+
+        if (cyclicWeight > 0 && maxAchievable < quorum)
+        {
+            JLOG(ctx.j.warn())
+                << "checkMultiSign: Cyclic lockout detected for " << acc
+                << ": relaxing quorum from " << quorum << " to "
+                << maxAchievable << " (total=" << totalWeight
+                << ", cyclic=" << cyclicWeight << ")";
+            effectiveQuorum = maxAchievable;
+        }
+
+        // Sanity check: effectiveQuorum of 0 means all signers are cyclic -
+        // this is an irrecoverable misconfiguration
+        if (effectiveQuorum == 0)
+        {
+            JLOG(ctx.j.warn()) << "checkMultiSign: All signers for " << acc
+                               << " are cyclic - no valid signing path exists.";
+            return tefBAD_QUORUM;
+        }
+
+        // Check if accumulated weight meets required quorum
+        if (sum < effectiveQuorum)
+        {
+            JLOG(ctx.j.trace()) << "checkMultiSign: Quorum not met for " << acc
+                                << " at depth " << depth << " (sum=" << sum
+                                << ", required=" << effectiveQuorum << ")";
+            return tefBAD_QUORUM;
+        }
+
+        return tesSUCCESS;
+    };
+
+    STArray const& entries(ctx.tx.getFieldArray(sfSigners));
+
+    // Initial call with empty ancestor set - the function inserts acc after
+    // cycle check
+    NotTEC result = validateSigners(id, entries, 1, {});
+    if (!isTesSuccess(result))
     {
         JLOG(ctx.j.trace())
-            << "applyTransaction: Signers failed to meet quorum.";
-        return tefBAD_QUORUM;
+            << "checkMultiSign: Validation failed with " << transToken(result);
+        return result;
     }
 
-    // Met the quorum.  Continue.
     return tesSUCCESS;
 }
 

src/ripple/protocol/Feature.h

@@ -74,7 +74,7 @@ namespace detail {
 // Feature.cpp. Because it's only used to reserve storage, and determine how
 // large to make the FeatureBitset, it MAY be larger. It MUST NOT be less than
 // the actual number of amendments. A LogicError on startup will verify this.
-static constexpr std::size_t numFeatures = 90;
+static constexpr std::size_t numFeatures = 91;
 
 /** Amendments that this server supports and the default voting behavior.
    Whether they are enabled depends on the Rules defined in the validated
@@ -378,6 +378,7 @@ extern uint256 const fixInvalidTxFlags;
 extern uint256 const featureExtendedHookState;
 extern uint256 const fixCronStacking;
 extern uint256 const fixHookAPI20251128;
+extern uint256 const featureNestedMultiSign;
 }  // namespace ripple
 
 #endif

src/ripple/protocol/impl/Feature.cpp

@@ -484,6 +484,7 @@ REGISTER_FIX    (fixInvalidTxFlags,             Supported::yes, VoteBehavior::De
 REGISTER_FEATURE(ExtendedHookState,             Supported::yes, VoteBehavior::DefaultNo);
 REGISTER_FIX    (fixCronStacking,               Supported::yes, VoteBehavior::DefaultYes);
 REGISTER_FIX    (fixHookAPI20251128,            Supported::yes, VoteBehavior::DefaultYes);
+REGISTER_FEATURE(NestedMultiSign,               Supported::yes, VoteBehavior::DefaultNo);
 
 // The following amendments are obsolete, but must remain supported
 // because they could potentially get enabled.

src/ripple/protocol/impl/InnerObjectFormats.cpp

@@ -44,8 +44,9 @@ InnerObjectFormats::InnerObjectFormats()
         sfSigner.getCode(),
         {
             {sfAccount, soeREQUIRED},
-            {sfSigningPubKey, soeREQUIRED},
-            {sfTxnSignature, soeREQUIRED},
+            {sfSigningPubKey, soeOPTIONAL},
+            {sfTxnSignature, soeOPTIONAL},
+            {sfSigners, soeOPTIONAL},
         });
 
     add(sfMajority.jsonName.c_str(),

src/ripple/protocol/impl/STTx.cpp

@@ -369,64 +369,146 @@ STTx::checkMultiSign(
     bool const fullyCanonical = (getFlags() & tfFullyCanonicalSig) ||
         (requireCanonicalSig == RequireFullyCanonicalSig::yes);
 
-    // Signers must be in sorted order by AccountID.
-    AccountID lastAccountID(beast::zero);
-
     bool const isWildcardNetwork =
         isFieldPresent(sfNetworkID) && getFieldU32(sfNetworkID) == 65535;
 
-    for (auto const& signer : signers)
-    {
-        auto const accountID = signer.getAccountID(sfAccount);
+    // Set max depth based on feature flag
+    int const maxDepth = rules.enabled(featureNestedMultiSign) ? 4 : 1;
 
-        // The account owner may not multisign for themselves.
-        if (accountID == txnAccountID)
-            return Unexpected("Invalid multisigner.");
+    // Define recursive lambda for checking signatures at any depth
+    std::function<Expected<void, std::string>(
+        STArray const&, AccountID const&, int)>
+        checkSignersArray;
 
-        // No duplicate signers allowed.
-        if (lastAccountID == accountID)
-            return Unexpected("Duplicate Signers not allowed.");
-
-        // Accounts must be in order by account ID.  No duplicates allowed.
-        if (lastAccountID > accountID)
-            return Unexpected("Unsorted Signers array.");
-
-        // The next signature must be greater than this one.
-        lastAccountID = accountID;
-
-        // Verify the signature.
-        bool validSig = false;
-        try
+    checkSignersArray = [&](STArray const& signersArray,
+                            AccountID const& parentAccountID,
+                            int depth) -> Expected<void, std::string> {
+        // Check depth limit
+        if (depth > maxDepth)
         {
-            Serializer s = dataStart;
-            finishMultiSigningData(accountID, s);
+            std::cout << "Multi-signing depth limit exceeded.\n";
+            return Unexpected("Multi-signing depth limit exceeded.");
+        }
 
-            auto spk = signer.getFieldVL(sfSigningPubKey);
+        // There are well known bounds that the number of signers must be
+        // within.
+        if (signersArray.size() < minMultiSigners ||
+            signersArray.size() > maxMultiSigners(&rules))
+        {
+            std::cout << "Invalid Signers array size.\n";
+            return Unexpected("Invalid Signers array size.");
+        }
 
-            if (publicKeyType(makeSlice(spk)))
+        // Signers must be in sorted order by AccountID.
+        AccountID lastAccountID(beast::zero);
+
+        for (auto const& signer : signersArray)
+        {
+            auto const accountID = signer.getAccountID(sfAccount);
+
+            // The account owner may not multisign for themselves.
+            if (accountID == txnAccountID)
             {
-                Blob const signature = signer.getFieldVL(sfTxnSignature);
+                std::cout << "Invalid multisigner.\n";
+                return Unexpected("Invalid multisigner.");
+            }
 
-                // wildcard network gets a free pass
-                validSig = isWildcardNetwork ||
-                    verify(PublicKey(makeSlice(spk)),
-                           s.slice(),
-                           makeSlice(signature),
-                           fullyCanonical);
+            // No duplicate signers allowed.
+            if (lastAccountID == accountID)
+            {
+                std::cout << "Duplicate Signers not allowed.\n";
+                return Unexpected("Duplicate Signers not allowed.");
+            }
+
+            // Accounts must be in order by account ID.  No duplicates allowed.
+            if (lastAccountID > accountID)
+            {
+                std::cout << "Unsorted Signers array.\n";
+                return Unexpected("Unsorted Signers array.");
+            }
+
+            // The next signature must be greater than this one.
+            lastAccountID = accountID;
+
+            // Check if this signer has nested signers
+            if (signer.isFieldPresent(sfSigners))
+            {
+                // This is a nested multi-signer
+                // Ensure it doesn't also have signature fields
+                if (signer.isFieldPresent(sfSigningPubKey) ||
+                    signer.isFieldPresent(sfTxnSignature))
+                {
+                    std::cout << "Signer cannot have both nested signers and "
+                                 "signature "
+                                 "fields.\n";
+                    return Unexpected(
+                        "Signer cannot have both nested signers and signature "
+                        "fields.");
+                }
+
+                // Recursively check nested signers
+                STArray const& nestedSigners = signer.getFieldArray(sfSigners);
+                auto result =
+                    checkSignersArray(nestedSigners, accountID, depth + 1);
+                if (!result)
+                    return result;
+            }
+            else
+            {
+                // This is a leaf node - must have signature
+                if (!signer.isFieldPresent(sfSigningPubKey) ||
+                    !signer.isFieldPresent(sfTxnSignature))
+                {
+                    std::cout << "Leaf signer must have SigningPubKey and "
+                                 "TxnSignature.\n";
+                    return Unexpected(
+                        "Leaf signer must have SigningPubKey and "
+                        "TxnSignature.");
+                }
+
+                // Verify the signature
+                bool validSig = false;
+                try
+                {
+                    Serializer s = dataStart;
+                    finishMultiSigningData(accountID, s);
+
+                    auto spk = signer.getFieldVL(sfSigningPubKey);
+
+                    if (publicKeyType(makeSlice(spk)))
+                    {
+                        Blob const signature =
+                            signer.getFieldVL(sfTxnSignature);
+
+                        // wildcard network gets a free pass
+                        validSig = isWildcardNetwork ||
+                            verify(PublicKey(makeSlice(spk)),
+                                   s.slice(),
+                                   makeSlice(signature),
+                                   fullyCanonical);
+                    }
+                }
+                catch (std::exception const&)
+                {
+                    // We assume any problem lies with the signature.
+                    validSig = false;
+                }
+                if (!validSig)
+                {
+                    std::cout << std::string("Invalid signature on account ") +
+                            toBase58(accountID) + ".\n";
+                    return Unexpected(
+                        std::string("Invalid signature on account ") +
+                        toBase58(accountID) + ".");
+                }
             }
         }
-        catch (std::exception const&)
-        {
-            // We assume any problem lies with the signature.
-            validSig = false;
-        }
-        if (!validSig)
-            return Unexpected(
-                std::string("Invalid signature on account ") +
-                toBase58(accountID) + ".");
-    }
-    // All signatures verified.
-    return {};
+
+        return {};
+    };
+
+    // Start the recursive check at depth 1
+    return checkSignersArray(signers, txnAccountID, 1);
 }
 
 //------------------------------------------------------------------------------

src/ripple/rpc/impl/TransactionSign.cpp

@@ -1183,12 +1183,21 @@ transactionSubmitMultiSigned(
     // The Signers array may only contain Signer objects.
     if (std::find_if_not(
             signers.begin(), signers.end(), [](STObject const& obj) {
-                return (
-                    // A Signer object always contains these fields and no
-                    // others.
-                    obj.isFieldPresent(sfAccount) &&
-                    obj.isFieldPresent(sfSigningPubKey) &&
-                    obj.isFieldPresent(sfTxnSignature) && obj.getCount() == 3);
+                if (obj.getCount() != 4 || !obj.isFieldPresent(sfAccount))
+                    return false;
+                // leaf signer
+                if (obj.isFieldPresent(sfSigningPubKey) &&
+                    obj.isFieldPresent(sfTxnSignature) &&
+                    !obj.isFieldPresent(sfSigners))
+                    return true;
+
+                // nested signer
+                if (!obj.isFieldPresent(sfSigningPubKey) &&
+                    !obj.isFieldPresent(sfTxnSignature) &&
+                    obj.isFieldPresent(sfSigners))
+                    return true;
+
+                return false;
             }) != signers.end())
     {
         return RPC::make_param_error(

src/test/app/MultiSign_test.cpp

@@ -1659,6 +1659,800 @@ public:
         BEAST_EXPECT(env.seq(alice) == aliceSeq + 1);
     }
 
+    void
+    test_nestedMultiSign(FeatureBitset features)
+    {
+        testcase("Nested MultiSign");
+
+#define STRINGIFY(x) #x
+#define TOSTRING(x) STRINGIFY(x)
+
+#define LINE_TO_HEX_STRING                                                \
+    []() -> std::string {                                                 \
+        const char* line = TOSTRING(__LINE__);                            \
+        int len = 0;                                                      \
+        while (line[len])                                                 \
+            len++;                                                        \
+        std::string result;                                               \
+        if (len % 2 == 1)                                                 \
+        {                                                                 \
+            result += (char)(0x00 * 16 + (line[0] - '0'));                \
+            line++;                                                       \
+        }                                                                 \
+        for (int i = 0; line[i]; i += 2)                                  \
+        {                                                                 \
+            result += (char)((line[i] - '0') * 16 + (line[i + 1] - '0')); \
+        }                                                                 \
+        return result;                                                    \
+    }()
+
+#define M(m) memo(m, "", "")
+#define L() memo(LINE_TO_HEX_STRING, "", "")
+
+        using namespace jtx;
+        Env env{*this, envconfig(), features};
+        // Env env{*this, envconfig(), features, nullptr,
+        // beast::severities::kTrace};
+
+        Account const alice{"alice", KeyType::secp256k1};
+        Account const becky{"becky", KeyType::ed25519};
+        Account const cheri{"cheri", KeyType::secp256k1};
+        Account const daria{"daria", KeyType::ed25519};
+        Account const edgar{"edgar", KeyType::secp256k1};
+        Account const fiona{"fiona", KeyType::ed25519};
+        Account const grace{"grace", KeyType::secp256k1};
+        Account const henry{"henry", KeyType::ed25519};
+        Account const f1{"f1", KeyType::ed25519};
+        Account const f2{"f2", KeyType::ed25519};
+        Account const f3{"f3", KeyType::ed25519};
+        env.fund(
+            XRP(1000),
+            alice,
+            becky,
+            cheri,
+            daria,
+            edgar,
+            fiona,
+            grace,
+            henry,
+            f1,
+            f2,
+            f3,
+            phase,
+            jinni,
+            acc10,
+            acc11,
+            acc12);
+        env.close();
+
+        auto const baseFee = env.current()->fees().base;
+
+        if (!features[featureNestedMultiSign])
+        {
+            // When feature is disabled, nested signing should fail
+            env(signers(f1, 1, {{f2, 1}}));
+            env(signers(f2, 1, {{f3, 1}}));
+            env.close();
+
+            std::uint32_t f1Seq = env.seq(f1);
+            env(noop(f1),
+                msig({msigner(f2, msigner(f3))}),
+                L(),
+                fee(3 * baseFee),
+                ter(temINVALID));
+            env.close();
+            BEAST_EXPECT(env.seq(f1) == f1Seq);
+            return;
+        }
+
+        // Test Case 1: Basic 2-level nested signing with quorum
+        {
+            // Set up signer lists with quorum requirements
+            env(signers(becky, 2, {{bogie, 1}, {demon, 1}, {ghost, 1}}));
+            env(signers(cheri, 3, {{haunt, 2}, {jinni, 2}}));
+            env.close();
+
+            // Alice requires quorum of 3 with weighted signers
+            env(signers(alice, 3, {{becky, 2}, {cheri, 2}, {daria, 1}}));
+            env.close();
+
+            // Test 1a: becky alone (weight 2) doesn't meet alice's quorum
+            std::uint32_t aliceSeq = env.seq(alice);
+            env(noop(alice),
+                msig({msigner(becky, msigner(bogie), msigner(demon))}),
+                L(),
+                fee(4 * baseFee),
+                ter(tefBAD_QUORUM));
+            env.close();
+            BEAST_EXPECT(env.seq(alice) == aliceSeq);
+
+            // Test 1b: becky (2) + daria (1) meets quorum of 3
+            aliceSeq = env.seq(alice);
+            env(noop(alice),
+                msig(
+                    {msigner(becky, msigner(bogie), msigner(demon)),
+                     msigner(daria)}),
+                L(),
+                fee(5 * baseFee));
+            env.close();
+            BEAST_EXPECT(env.seq(alice) == aliceSeq + 1);
+
+            // Test 1c: cheri's nested signers must meet her quorum
+            aliceSeq = env.seq(alice);
+            env(noop(alice),
+                msig(
+                    {msigner(
+                         becky,
+                         msigner(bogie),
+                         msigner(demon)),  // becky has a satisfied quorum
+                     msigner(cheri, msigner(haunt))}),  // but cheri does not
+                                                        // (needs jinni too)
+                L(),
+                fee(5 * baseFee),
+                ter(tefBAD_QUORUM));
+            env.close();
+            BEAST_EXPECT(env.seq(alice) == aliceSeq);
+
+            // Test 1d: cheri with both signers meets her quorum
+            aliceSeq = env.seq(alice);
+            env(noop(alice),
+                msig(
+                    {msigner(cheri, msigner(haunt), msigner(jinni)),
+                     msigner(daria)}),
+                L(),
+                fee(5 * baseFee));
+            env.close();
+            BEAST_EXPECT(env.seq(alice) == aliceSeq + 1);
+        }
+
+        // Test Case 2: 3-level maximum depth with quorum at each level
+        {
+            // Level 2: phase needs direct signatures (no deeper nesting)
+            env(signers(phase, 2, {{acc10, 1}, {acc11, 1}, {acc12, 1}}));
+
+            // Level 1: jinni needs weighted signatures
+            env(signers(jinni, 3, {{phase, 2}, {shade, 2}, {spook, 1}}));
+
+            // Level 0: edgar needs 2 from weighted signers
+            env(signers(edgar, 2, {{jinni, 1}, {bogie, 1}, {demon, 1}}));
+
+            // Alice now requires edgar with weight 3
+            env(signers(alice, 3, {{edgar, 3}, {fiona, 2}}));
+            env.close();
+
+            // Test 2a: 3-level signing with phase signing directly (not through
+            // nested signers)
+            std::uint32_t aliceSeq = env.seq(alice);
+            env(noop(alice),
+                msig({
+                    msigner(
+                        edgar,
+                        msigner(
+                            jinni,
+                            msigner(phase),  // phase signs directly at level 3
+                            msigner(shade))  // jinni quorum: 2+2 = 4 >= 3 ✓
+                        )                    // edgar quorum: 1+0 = 1 < 2 ✗
+                }),
+                L(),
+                fee(4 * baseFee),
+                ter(tefBAD_QUORUM));
+            env.close();
+            BEAST_EXPECT(env.seq(alice) == aliceSeq);
+
+            // Test 2b: Edgar needs to meet his quorum too
+            aliceSeq = env.seq(alice);
+            env(noop(alice),
+                msig({
+                    msigner(
+                        edgar,
+                        msigner(
+                            jinni,
+                            msigner(phase),  // phase signs directly
+                            msigner(shade)),
+                        msigner(bogie))  // edgar quorum: 1+1 = 2 ✓
+                }),
+                L(),
+                fee(5 * baseFee));
+            env.close();
+            BEAST_EXPECT(env.seq(alice) == aliceSeq + 1);
+
+            // Test 2c: Use phase's signers (making it effectively 3-level from
+            // alice)
+            aliceSeq = env.seq(alice);
+            env(noop(alice),
+                msig({msigner(
+                    edgar,
+                    msigner(
+                        jinni,
+                        msigner(phase, msigner(acc10), msigner(acc11)),
+                        msigner(spook)),
+                    msigner(bogie))}),
+                L(),
+                fee(6 * baseFee));
+            env.close();
+            BEAST_EXPECT(env.seq(alice) == aliceSeq + 1);
+        }
+
+        // Test Case 3: Mixed levels - some direct, some nested at different
+        // depths (max 3)
+        {
+            // Set up mixed-level signing for alice
+            // grace has direct signers
+            env(signers(grace, 2, {{bogie, 1}, {demon, 1}}));
+
+            // henry has 2-level signers (henry -> becky -> bogie/demon)
+            env(signers(henry, 1, {{becky, 1}, {cheri, 1}}));
+
+            // edgar can be signed for by bogie
+            env(signers(edgar, 1, {{bogie, 1}, {shade, 1}}));
+
+            // Alice has mix of direct and nested signers at different weights
+            env(signers(
+                alice,
+                5,
+                {
+                    {daria, 1},  // direct signer
+                    {edgar, 2},  // has 2-level signers
+                    {fiona, 1},  // direct signer
+                    {grace, 2},  // has direct signers
+                    {henry, 2}   // has 2-level signers
+                }));
+            env.close();
+
+            // Test 3a: Mix of all levels meeting quorum exactly
+            std::uint32_t aliceSeq = env.seq(alice);
+            env(noop(alice),
+                msig({
+                    msigner(daria),                  // weight 1, direct
+                    msigner(edgar, msigner(bogie)),  // weight 2, 2-level
+                    msigner(grace, msigner(bogie), msigner(demon))  // weight 2,
+                                                                    // 2-level
+                }),
+                L(),
+                fee(6 * baseFee));
+            env.close();
+            BEAST_EXPECT(env.seq(alice) == aliceSeq + 1);
+
+            // Test 3b: 3-level signing through henry
+            aliceSeq = env.seq(alice);
+            env(noop(alice),
+                msig(
+                    {msigner(fiona),  // weight 1, direct
+                     msigner(
+                         grace, msigner(bogie)),  // weight 2, 2-level (partial)
+                     msigner(
+                         henry,  // weight 2, 3-level
+                         msigner(becky, msigner(bogie), msigner(demon)))}),
+                L(),
+                fee(6 * baseFee),
+                ter(tefBAD_QUORUM));  // grace didn't meet quorum
+            env.close();
+            BEAST_EXPECT(env.seq(alice) == aliceSeq);
+
+            // Test 3c: Correct version with all quorums met
+            aliceSeq = env.seq(alice);
+            env(noop(alice),
+                msig(
+                    {msigner(fiona),  // weight 1
+                     msigner(
+                         edgar, msigner(bogie), msigner(shade)),  // weight 2
+                     msigner(
+                         henry,  // weight 2
+                         msigner(becky, msigner(bogie), msigner(demon)))}),
+                L(),
+                fee(8 * baseFee));  // Total weight: 1+2+2 = 5 ✓
+            env.close();
+            BEAST_EXPECT(env.seq(alice) == aliceSeq + 1);
+        }
+
+        // Test Case 4: Complex scenario with maximum signers at mixed depths
+        // (max 3)
+        {
+            // Create a signing tree that uses close to maximum signers
+            // and tests weight accumulation across all levels
+
+            // Set up for alice: needs 15 out of possible 20 weight
+            env(signers(
+                alice,
+                15,
+                {
+                    {becky, 3},  // will use 2-level
+                    {cheri, 3},  // will use 2-level
+                    {daria, 3},  // will use direct
+                    {edgar, 3},  // will use 2-level
+                    {fiona, 3},  // will use direct
+                    {grace, 3},  // will use direct
+                    {henry, 2}   // will use 2-level
+                }));
+            env.close();
+
+            // Complex multi-level transaction just meeting quorum
+            std::uint32_t aliceSeq = env.seq(alice);
+            env(noop(alice),
+                msig({
+                    msigner(
+                        becky,  // weight 3, 2-level
+                        msigner(demon),
+                        msigner(ghost)),
+                    msigner(
+                        cheri,  // weight 3, 2-level
+                        msigner(haunt),
+                        msigner(jinni)),
+                    msigner(daria),  // weight 3, direct
+                    msigner(
+                        edgar,  // weight 3, 2-level
+                        msigner(bogie)),
+                    msigner(grace)  // weight 3, direct
+                }),
+                L(),
+                fee(10 * baseFee));  // Total weight: 3+3+3+3+3 = 15 ✓
+            env.close();
+            BEAST_EXPECT(env.seq(alice) == aliceSeq + 1);
+
+            // Test 4b: Test with henry using 3-level depth (maximum)
+            // First set up henry's chain properly
+            env(signers(henry, 1, {{jinni, 1}}));
+            env(signers(jinni, 2, {{acc10, 1}, {acc11, 1}}));
+            env.close();
+
+            aliceSeq = env.seq(alice);
+            env(noop(alice),
+                msig(
+                    {msigner(
+                         becky,            // weight 3
+                         msigner(demon)),  // becky quorum not met!
+                     msigner(
+                         cheri,  // weight 3
+                         msigner(haunt),
+                         msigner(jinni)),
+                     msigner(daria),  // weight 3
+                     msigner(
+                         henry,  // weight 2, 3-level depth
+                         msigner(jinni, msigner(acc10), msigner(acc11))),
+                     msigner(
+                         edgar,  // weight 3
+                         msigner(bogie),
+                         msigner(shade))}),
+                L(),
+                fee(10 * baseFee),
+                ter(tefBAD_QUORUM));  // becky's quorum not met
+            env.close();
+            BEAST_EXPECT(env.seq(alice) == aliceSeq);
+        }
+
+        // Test Case 5: Edge case - single signer with maximum nesting (depth 3)
+        {
+            // Alice needs just one signer, but that signer uses depth up to 3
+            env(signers(alice, 1, {{becky, 1}}));
+            env.close();
+
+            std::uint32_t aliceSeq = env.seq(alice);
+            env(noop(alice),
+                msig({msigner(becky, msigner(demon), msigner(ghost))}),
+                L(),
+                fee(4 * baseFee));
+            env.close();
+            BEAST_EXPECT(env.seq(alice) == aliceSeq + 1);
+
+            // Now with 3-level depth (maximum allowed)
+            // Structure: alice -> becky -> cheri -> jinni (jinni signs
+            // directly)
+            env(signers(becky, 1, {{cheri, 1}}));
+            env(signers(cheri, 1, {{jinni, 1}}));
+            // Note: We do NOT add signers to jinni to keep max depth at 3
+            env.close();
+
+            aliceSeq = env.seq(alice);
+            env(noop(alice),
+                msig({msigner(
+                    becky,
+                    msigner(
+                        cheri,
+                        msigner(jinni)))}),  // jinni signs directly (depth 3)
+                L(),
+                fee(4 * baseFee));
+            env.close();
+            BEAST_EXPECT(env.seq(alice) == aliceSeq + 1);
+        }
+
+        // Test Case 6: Simple cycle detection (A -> B -> A)
+        {
+            testcase("Cycle Detection - Simple");
+
+            // Reset signer lists for clean state
+            env(signers(alice, jtx::none));
+            env(signers(becky, jtx::none));
+            env.close();
+
+            // becky's signer list includes alice
+            // alice's signer list includes becky
+            // This creates: alice -> becky -> alice (cycle)
+            env(signers(alice, 1, {{becky, 1}, {bogie, 1}}));
+            env(signers(becky, 1, {{alice, 1}, {demon, 1}}));
+            env.close();
+
+            // Without cycle relaxation this would fail because:
+            // - alice needs becky (weight 1)
+            // - becky needs alice, but alice is ancestor -> cycle
+            // - becky's effective quorum relaxes since alice is unavailable
+            // - demon can satisfy becky's relaxed quorum
+            std::uint32_t aliceSeq = env.seq(alice);
+            env(noop(alice),
+                msig({msigner(becky, msigner(demon))}),
+                L(),
+                fee(4 * baseFee));
+            env.close();
+            BEAST_EXPECT(env.seq(alice) == aliceSeq + 1);
+
+            // Test that direct signer still works normally
+            aliceSeq = env.seq(alice);
+            env(noop(alice), msig({msigner(bogie)}), L(), fee(3 * baseFee));
+            env.close();
+            BEAST_EXPECT(env.seq(alice) == aliceSeq + 1);
+        }
+
+        // Test Case 7: The specific lockout scenario
+        // onyx:{jade, nova:{ruby:{jade, nova}, jade}}
+        // All have quorum 2, only jade can actually sign
+        {
+            testcase("Cycle Detection - Complex Lockout");
+
+            Account const onyx{"onyx", KeyType::secp256k1};
+            Account const nova{"nova", KeyType::ed25519};
+            Account const ruby{"ruby", KeyType::secp256k1};
+            Account const jade{"jade", KeyType::ed25519};  // phantom signer
+
+            env.fund(XRP(1000), onyx, nova, ruby);
+            env.close();
+
+            // Set up signer lists FIRST (before disabling master keys)
+            // ruby: {jade, nova} with quorum 2
+            env(signers(ruby, 2, {{jade, 1}, {nova, 1}}));
+            // nova: {ruby, jade} with quorum 2
+            env(signers(nova, 2, {{jade, 1}, {ruby, 1}}));
+            // onyx: {jade, nova} with quorum 2
+            env(signers(onyx, 2, {{jade, 1}, {nova, 1}}));
+            env.close();
+
+            // NOW disable master keys (signer lists provide alternative)
+            env(fset(onyx, asfDisableMaster), sig(onyx));
+            env(fset(nova, asfDisableMaster), sig(nova));
+            env(fset(ruby, asfDisableMaster), sig(ruby));
+            env.close();
+
+            // The signing tree for onyx:
+            // onyx (quorum 2) -> jade (weight 1) + nova (weight 1)
+            //   nova (quorum 2) -> jade (weight 1) + ruby (weight 1)
+            //     ruby (quorum 2) -> jade (weight 1) + nova (weight 1, CYCLE!)
+            //
+            // Without cycle detection: ruby needs nova, but nova is ancestor ->
+            // stuck With cycle detection:
+            //   - At ruby level: nova is cyclic, cyclicWeight=1, totalWeight=2
+            //   - maxAchievable = 2-1 = 1 < quorum(2), so effectiveQuorum -> 1
+            //   - jade alone can satisfy ruby's relaxed quorum
+            //   - ruby satisfied -> nova gets ruby's weight
+            //   - nova: jade(1) + ruby(1) = 2 >= quorum(2) ✓
+            //   - onyx: jade(1) + nova(1) = 2 >= quorum(2) ✓
+
+            std::uint32_t onyxSeq = env.seq(onyx);
+            env(noop(onyx),
+                msig(
+                    {msigner(jade),
+                     msigner(
+                         nova,
+                         msigner(jade),
+                         msigner(
+                             ruby, msigner(jade)))}),  // nova is cyclic,
+                                                       // skipped at ruby level
+                L(),
+                fee(6 * baseFee));
+            env.close();
+            BEAST_EXPECT(env.seq(onyx) == onyxSeq + 1);
+        }
+
+        // Test Case 8: Cycle where all signers are cyclic (effectiveQuorum ==
+        // 0)
+        {
+            testcase("Cycle Detection - Total Lockout");
+
+            Account const alpha{"alpha", KeyType::secp256k1};
+            Account const beta{"beta", KeyType::ed25519};
+            Account const gamma{"gamma", KeyType::secp256k1};
+
+            env.fund(XRP(1000), alpha, beta, gamma);
+            env.close();
+
+            // Set up pure cycle signer lists FIRST
+            env(signers(alpha, 1, {{beta, 1}}));
+            env(signers(beta, 1, {{gamma, 1}}));
+            env(signers(gamma, 1, {{alpha, 1}}));
+            env.close();
+
+            // NOW disable master keys
+            env(fset(alpha, asfDisableMaster), sig(alpha));
+            env(fset(beta, asfDisableMaster), sig(beta));
+            env(fset(gamma, asfDisableMaster), sig(gamma));
+            env.close();
+
+            // This is a true lockout - no valid signing path exists.
+            // gamma appears as a leaf signer but has master disabled ->
+            // tefMASTER_DISABLED (The cycle detection would return
+            // tefBAD_QUORUM if gamma were nested, but there's no way to
+            // construct such a transaction since gamma's only signer is alpha,
+            // which is what we're trying to sign for)
+            std::uint32_t alphaSeq = env.seq(alpha);
+            env(noop(alpha),
+                msig({msigner(
+                    beta,
+                    msigner(gamma))}),  // gamma can't sign - master disabled
+                L(),
+                fee(4 * baseFee),
+                ter(tefMASTER_DISABLED));
+            env.close();
+            BEAST_EXPECT(env.seq(alpha) == alphaSeq);
+        }
+
+        // Test Case 9: Cycle at depth 3 (near max depth)
+        {
+            testcase("Cycle Detection - Deep Cycle");
+
+            // Reset signer lists
+            env(signers(alice, jtx::none));
+            env(signers(becky, jtx::none));
+            env(signers(cheri, jtx::none));
+            env(signers(daria, jtx::none));
+            env.close();
+
+            // Structure: alice -> becky -> cheri -> daria -> alice (cycle at
+            // depth 4)
+            env(signers(alice, 1, {{becky, 1}, {bogie, 1}}));
+            env(signers(becky, 1, {{cheri, 1}}));
+            env(signers(cheri, 1, {{daria, 1}}));
+            env(signers(daria, 1, {{alice, 1}, {demon, 1}}));
+            env.close();
+
+            // At depth 4, daria needs alice but alice is ancestor
+            // daria's quorum relaxes, demon can satisfy
+            std::uint32_t aliceSeq = env.seq(alice);
+            env(noop(alice),
+                msig({msigner(
+                    becky, msigner(cheri, msigner(daria, msigner(demon))))}),
+                L(),
+                fee(6 * baseFee));
+            env.close();
+            BEAST_EXPECT(env.seq(alice) == aliceSeq + 1);
+        }
+
+        // Test Case 10: Multiple independent cycles in same tree
+        {
+            testcase("Cycle Detection - Multiple Cycles");
+
+            // Reset signer lists
+            env(signers(alice, jtx::none));
+            env(signers(becky, jtx::none));
+            env(signers(cheri, jtx::none));
+            env.close();
+
+            // alice -> {becky, cheri}
+            // becky -> {alice, bogie}  (cycle back to alice)
+            // cheri -> {alice, demon}  (another cycle back to alice)
+            env(signers(alice, 2, {{becky, 1}, {cheri, 1}}));
+            env(signers(becky, 2, {{alice, 1}, {bogie, 1}}));
+            env(signers(cheri, 2, {{alice, 1}, {demon, 1}}));
+            env.close();
+
+            // Both becky and cheri have cycles back to alice
+            // Both need their quorums relaxed
+            // bogie satisfies becky, demon satisfies cheri
+            std::uint32_t aliceSeq = env.seq(alice);
+            env(noop(alice),
+                msig(
+                    {msigner(becky, msigner(bogie)),
+                     msigner(cheri, msigner(demon))}),
+                L(),
+                fee(6 * baseFee));
+            env.close();
+            BEAST_EXPECT(env.seq(alice) == aliceSeq + 1);
+        }
+
+        // Test Case 11: Cycle with sufficient non-cyclic weight (no relaxation
+        // needed)
+        {
+            testcase("Cycle Detection - No Relaxation Needed");
+
+            // Reset signer lists
+            env(signers(alice, jtx::none));
+            env(signers(becky, jtx::none));
+            env.close();
+
+            // becky has alice in signer list but also has enough other signers
+            env(signers(alice, 1, {{becky, 1}}));
+            env(signers(becky, 2, {{alice, 1}, {bogie, 1}, {demon, 1}}));
+            env.close();
+
+            // becky quorum is 2, alice is cyclic (weight 1)
+            // totalWeight = 3, cyclicWeight = 1, maxAchievable = 2 >= quorum
+            // No relaxation needed, bogie + demon satisfy quorum normally
+            std::uint32_t aliceSeq = env.seq(alice);
+            env(noop(alice),
+                msig({msigner(becky, msigner(bogie), msigner(demon))}),
+                L(),
+                fee(5 * baseFee));
+            env.close();
+            BEAST_EXPECT(env.seq(alice) == aliceSeq + 1);
+
+            // Should fail if only one non-cyclic signer provided
+            aliceSeq = env.seq(alice);
+            env(noop(alice),
+                msig({msigner(becky, msigner(bogie))}),
+                L(),
+                fee(4 * baseFee),
+                ter(tefBAD_QUORUM));
+            env.close();
+            BEAST_EXPECT(env.seq(alice) == aliceSeq);
+        }
+
+        // Test Case 12: Partial cycle - one branch cyclic, one not
+        {
+            testcase("Cycle Detection - Partial Cycle");
+
+            // Reset signer lists
+            env(signers(alice, jtx::none));
+            env(signers(becky, jtx::none));
+            env(signers(cheri, jtx::none));
+            env.close();
+
+            // alice -> {becky, cheri}
+            // becky -> {alice, bogie}  (cyclic)
+            // cheri -> {daria}  (not cyclic)
+            env(signers(alice, 2, {{becky, 1}, {cheri, 1}}));
+            env(signers(becky, 1, {{alice, 1}, {bogie, 1}}));
+            env(signers(cheri, 1, {{daria, 1}}));
+            env.close();
+
+            // becky's branch has cycle, cheri's doesn't
+            // Both contribute to alice's quorum
+            std::uint32_t aliceSeq = env.seq(alice);
+            env(noop(alice),
+                msig(
+                    {msigner(becky, msigner(bogie)),    // relaxed quorum
+                     msigner(cheri, msigner(daria))}),  // normal quorum
+                L(),
+                fee(6 * baseFee));
+            env.close();
+            BEAST_EXPECT(env.seq(alice) == aliceSeq + 1);
+        }
+
+        // Test Case 13: Diamond pattern with cycle
+        {
+            testcase("Cycle Detection - Diamond Pattern");
+
+            // Reset signer lists
+            env(signers(alice, jtx::none));
+            env(signers(becky, jtx::none));
+            env(signers(cheri, jtx::none));
+            env(signers(daria, jtx::none));
+            env.close();
+
+            // alice -> {becky, cheri}
+            // becky -> {daria}
+            // cheri -> {daria}
+            // daria -> {alice, bogie}  (cycle through both paths)
+            env(signers(alice, 2, {{becky, 1}, {cheri, 1}}));
+            env(signers(becky, 1, {{daria, 1}}));
+            env(signers(cheri, 1, {{daria, 1}}));
+            env(signers(daria, 1, {{alice, 1}, {bogie, 1}}));
+            env.close();
+
+            // Both paths converge at daria, which cycles back to alice
+            std::uint32_t aliceSeq = env.seq(alice);
+            env(noop(alice),
+                msig(
+                    {msigner(becky, msigner(daria, msigner(bogie))),
+                     msigner(cheri, msigner(daria, msigner(bogie)))}),
+                L(),
+                fee(7 * baseFee));
+            env.close();
+            BEAST_EXPECT(env.seq(alice) == aliceSeq + 1);
+        }
+
+        // Test Case 14: Cycle requiring maximum quorum relaxation
+        {
+            testcase("Cycle Detection - Maximum Relaxation");
+
+            Account const omega{"omega", KeyType::secp256k1};
+            Account const sigma{"sigma", KeyType::ed25519};
+
+            env.fund(XRP(1000), omega, sigma);
+            env.close();
+
+            // Reset alice and becky signer lists
+            env(signers(alice, jtx::none));
+            env(signers(becky, jtx::none));
+            env.close();
+
+            // Set up signer lists FIRST
+            env(signers(sigma, 1, {{omega, 1}, {bogie, 1}}));
+            env(signers(omega, 3, {{sigma, 2}, {alice, 1}, {becky, 1}}));
+            env(signers(alice, 1, {{omega, 1}, {demon, 1}}));
+            env(signers(becky, 1, {{omega, 1}, {ghost, 1}}));
+            env.close();
+
+            // NOW disable master keys
+            env(fset(omega, asfDisableMaster), sig(omega));
+            env(fset(sigma, asfDisableMaster), sig(sigma));
+            env.close();
+
+            // From omega's perspective when signing for omega:
+            // - sigma: needs omega (cyclic), so relaxes to bogie only
+            // - alice: needs omega (cyclic), so relaxes to demon only
+            // - becky: needs omega (cyclic), so relaxes to ghost only
+            // All signers need relaxation but can be satisfied
+            std::uint32_t omegaSeq = env.seq(omega);
+            env(noop(omega),
+                msig(
+                    {msigner(alice, msigner(demon)),
+                     msigner(becky, msigner(ghost)),
+                     msigner(sigma, msigner(bogie))}),
+                L(),
+                fee(7 * baseFee));
+            env.close();
+            BEAST_EXPECT(env.seq(omega) == omegaSeq + 1);
+        }
+
+        // Test Case 15: Cycle at exact max depth boundary
+        {
+            testcase("Cycle Detection - Max Depth Boundary");
+
+            // Reset signer lists
+            env(signers(alice, jtx::none));
+            env(signers(becky, jtx::none));
+            env(signers(cheri, jtx::none));
+            env(signers(daria, jtx::none));
+            env(signers(edgar, jtx::none));
+            env.close();
+
+            // Depth 4 is max: alice(1) -> becky(2) -> cheri(3) -> daria(4)
+            // daria cycles back but we're at max depth
+            env(signers(alice, 1, {{becky, 1}}));
+            env(signers(becky, 1, {{cheri, 1}}));
+            env(signers(cheri, 1, {{daria, 1}}));
+            env(signers(daria, 1, {{alice, 1}, {bogie, 1}}));
+            env.close();
+
+            // This should work - cycle detected and relaxed at depth 4
+            std::uint32_t aliceSeq = env.seq(alice);
+            env(noop(alice),
+                msig({msigner(
+                    becky, msigner(cheri, msigner(daria, msigner(bogie))))}),
+                L(),
+                fee(6 * baseFee));
+            env.close();
+            BEAST_EXPECT(env.seq(alice) == aliceSeq + 1);
+
+            // Now try to exceed depth (add edgar at depth 5)
+            env(signers(daria, 1, {{edgar, 1}}));
+            env(signers(edgar, 1, {{bogie, 1}}));
+            env.close();
+
+            // Transaction structure is rejected at preflight for exceeding
+            // nesting limits
+            aliceSeq = env.seq(alice);
+            env(noop(alice),
+                msig({msigner(
+                    becky,
+                    msigner(
+                        cheri,
+                        msigner(daria, msigner(edgar, msigner(bogie)))))}),
+                L(),
+                fee(7 * baseFee),
+                ter(temMALFORMED));  // Rejected at preflight for excessive
+                                     // nesting
+            env.close();
+            BEAST_EXPECT(env.seq(alice) == aliceSeq);
+        }
+    }
+
     void
     test_signerListSetFlags(FeatureBitset features)
     {
@@ -1709,6 +2503,7 @@ public:
         test_signForHash(features);
         test_signersWithTickets(features);
         test_signersWithTags(features);
+        test_nestedMultiSign(features);
     }
 
     void
@@ -1721,8 +2516,11 @@ public:
         // featureMultiSignReserve.  Limits on the number of signers
         // changes based on featureExpandedSignerList.  Test both with and
         // without.
-        testAll(all - featureMultiSignReserve - featureExpandedSignerList);
-        testAll(all - featureExpandedSignerList);
+        testAll(
+            all - featureMultiSignReserve - featureExpandedSignerList -
+            featureNestedMultiSign);
+        testAll(all - featureExpandedSignerList - featureNestedMultiSign);
+        testAll(all - featureNestedMultiSign);
         testAll(all);
 
         test_signerListSetFlags(all);

src/test/jtx/impl/multisign.cpp

@@ -66,15 +66,45 @@ signers(Account const& account, none_t)
 
 //------------------------------------------------------------------------------
 
-msig::msig(std::vector<msig::Reg> signers_) : signers(std::move(signers_))
+// Helper function to recursively sort nested signers
+void
+sortSignersRecursive(std::vector<msig::SignerPtr>& signers)
 {
-    // Signatures must be applied in sorted order.
+    // Sort current level by account ID
     std::sort(
         signers.begin(),
         signers.end(),
-        [](msig::Reg const& lhs, msig::Reg const& rhs) {
-            return lhs.acct.id() < rhs.acct.id();
+        [](msig::SignerPtr const& lhs, msig::SignerPtr const& rhs) {
+            return lhs->id() < rhs->id();
         });
+
+    // Recursively sort nested signers for each signer at this level
+    for (auto& signer : signers)
+    {
+        if (signer->isNested() && !signer->nested.empty())
+        {
+            sortSignersRecursive(signer->nested);
+        }
+    }
+}
+
+msig::msig(std::vector<msig::SignerPtr> signers_) : signers(std::move(signers_))
+{
+    // Recursively sort all signers at all nesting levels
+    // This ensures account IDs are in strictly ascending order at each level
+    sortSignersRecursive(signers);
+}
+
+msig::msig(std::vector<msig::Reg> signers_)
+{
+    // Convert Reg vector to SignerPtr vector for backward compatibility
+    signers.reserve(signers_.size());
+    for (auto const& s : signers_)
+        signers.push_back(s.toSigner());
+
+    // Recursively sort all signers at all nesting levels
+    // This ensures account IDs are in strictly ascending order at each level
+    sortSignersRecursive(signers);
 }
 
 void
@@ -93,19 +123,47 @@ msig::operator()(Env& env, JTx& jt) const
             env.test.log << pretty(jtx.jv) << std::endl;
             Rethrow();
         }
+
+        // Recursive function to build signer JSON
+        std::function<Json::Value(SignerPtr const&)> buildSignerJson;
+        buildSignerJson = [&](SignerPtr const& signer) -> Json::Value {
+            Json::Value jo;
+            jo[jss::Account] = signer->acct.human();
+
+            if (signer->isNested())
+            {
+                // For nested signers, we use the already-sorted nested vector
+                // (sorted during construction via sortSignersRecursive)
+                // This ensures account IDs are in strictly ascending order
+                auto& subJs = jo[sfSigners.getJsonName()];
+                for (std::size_t i = 0; i < signer->nested.size(); ++i)
+                {
+                    auto& subJo = subJs[i][sfSigner.getJsonName()];
+                    subJo = buildSignerJson(signer->nested[i]);
+                }
+            }
+            else
+            {
+                // This is a leaf signer - add signature
+                jo[jss::SigningPubKey] = strHex(signer->sig.pk().slice());
+
+                Serializer ss{buildMultiSigningData(*st, signer->acct.id())};
+                auto const sig = ripple::sign(
+                    *publicKeyType(signer->sig.pk().slice()),
+                    signer->sig.sk(),
+                    ss.slice());
+                jo[sfTxnSignature.getJsonName()] =
+                    strHex(Slice{sig.data(), sig.size()});
+            }
+
+            return jo;
+        };
+
         auto& js = jtx[sfSigners.getJsonName()];
         for (std::size_t i = 0; i < mySigners.size(); ++i)
         {
-            auto const& e = mySigners[i];
             auto& jo = js[i][sfSigner.getJsonName()];
-            jo[jss::Account] = e.acct.human();
-            jo[jss::SigningPubKey] = strHex(e.sig.pk().slice());
-
-            Serializer ss{buildMultiSigningData(*st, e.acct.id())};
-            auto const sig = ripple::sign(
-                *publicKeyType(e.sig.pk().slice()), e.sig.sk(), ss.slice());
-            jo[sfTxnSignature.getJsonName()] =
-                strHex(Slice{sig.data(), sig.size()});
+            jo = buildSignerJson(mySigners[i]);
         }
     };
 }

src/test/jtx/multisign.h

@@ -21,6 +21,7 @@
 #define RIPPLE_TEST_JTX_MULTISIGN_H_INCLUDED
 
 #include <cstdint>
+#include <memory>
 #include <optional>
 #include <test/jtx/Account.h>
 #include <test/jtx/amount.h>
@@ -65,6 +66,48 @@ signers(Account const& account, none_t);
 class msig
 {
 public:
+    // Recursive signer structure
+    struct Signer
+    {
+        Account acct;
+        Account sig;  // For leaf signers (same as acct for master key)
+        std::vector<std::shared_ptr<Signer>> nested;  // For nested signers
+
+        // Leaf signer constructor (regular signing)
+        Signer(Account const& masterSig) : acct(masterSig), sig(masterSig)
+        {
+        }
+
+        // Leaf signer constructor (with different signing key)
+        Signer(Account const& acct_, Account const& regularSig)
+            : acct(acct_), sig(regularSig)
+        {
+        }
+
+        // Nested signer constructor
+        Signer(
+            Account const& acct_,
+            std::vector<std::shared_ptr<Signer>> nested_)
+            : acct(acct_), nested(std::move(nested_))
+        {
+        }
+
+        bool
+        isNested() const
+        {
+            return !nested.empty();
+        }
+
+        AccountID
+        id() const
+        {
+            return acct.id();
+        }
+    };
+
+    using SignerPtr = std::shared_ptr<Signer>;
+
+    // For backward compatibility
     struct Reg
     {
         Account acct;
@@ -73,16 +116,13 @@ public:
         Reg(Account const& masterSig) : acct(masterSig), sig(masterSig)
         {
         }
-
         Reg(Account const& acct_, Account const& regularSig)
             : acct(acct_), sig(regularSig)
         {
         }
-
         Reg(char const* masterSig) : acct(masterSig), sig(masterSig)
         {
         }
-
         Reg(char const* acct_, char const* regularSig)
             : acct(acct_), sig(regularSig)
         {
@@ -93,13 +133,25 @@ public:
         {
             return acct < rhs.acct;
         }
+
+        // Convert to Signer
+        SignerPtr
+        toSigner() const
+        {
+            return std::make_shared<Signer>(acct, sig);
+        }
     };
 
-    std::vector<Reg> signers;
+    std::vector<SignerPtr> signers;
 
 public:
+    // Direct constructor with SignerPtr vector
+    msig(std::vector<SignerPtr> signers_);
+
+    // Backward compatibility constructor
     msig(std::vector<Reg> signers_);
 
+    // Variadic constructor for backward compatibility
     template <class AccountType, class... Accounts>
     explicit msig(AccountType&& a0, Accounts&&... aN)
         : msig{std::vector<Reg>{
@@ -112,6 +164,30 @@ public:
     operator()(Env&, JTx& jt) const;
 };
 
+// Helper functions to create signers - renamed to avoid conflict with sig()
+// transaction modifier
+inline msig::SignerPtr
+msigner(Account const& acct)
+{
+    return std::make_shared<msig::Signer>(acct);
+}
+
+inline msig::SignerPtr
+msigner(Account const& acct, Account const& signingKey)
+{
+    return std::make_shared<msig::Signer>(acct, signingKey);
+}
+
+// Create nested signer with initializer list
+template <typename... Args>
+inline msig::SignerPtr
+msigner(Account const& acct, Args&&... args)
+{
+    std::vector<msig::SignerPtr> nested;
+    (nested.push_back(std::forward<Args>(args)), ...);
+    return std::make_shared<msig::Signer>(acct, std::move(nested));
+}
+
 //------------------------------------------------------------------------------
 
 /** The number of signer lists matches. */

src/test/unit_test/multi_runner.h

@@ -332,6 +332,7 @@ multi_runner_child::run_multi(Pred pred)
     {
         if (!pred(*t))
             continue;
+
         try
         {
             failed = run(*t) || failed;