chore: Bump version to 3.2.1

Bound the number of manifests carried in a single TMManifests message
(kMaxManifestsPerMessage). Trusted manifests are always included and
processed; untrusted gossip is capped per message on both send and
receive, and the sender is charged only when untrusted entries are
actually skipped. Oversized TMManifests messages are dropped without
penalty at the protocol layer so an unpatched peer is not disconnected.

Complements the cache bound from #276/#323.

include/xrpl/basics/base64.h

@@ -39,6 +39,35 @@
 
 namespace xrpl {
 
+namespace base64 {
+
+/**
+ * Returns the maximum number of characters needed to base64-encode @p nBytes bytes.
+ *
+ * @param nBytes Number of input bytes.
+ * @return Size of the encoded string, including padding.
+ */
+constexpr std::size_t
+encodedSize(std::size_t const nBytes)
+{
+    return 4 * ((nBytes + 2) / 3);
+}
+
+/**
+ * Returns the maximum number of bytes a base64 string of @p numChars characters
+ * decodes to.
+ *
+ * @param numChars Number of base64 characters.
+ * @return Upper bound on the number of decoded bytes.
+ */
+constexpr std::size_t
+decodedSize(std::size_t const numChars)
+{
+    return ((numChars / 4) * 3) + 2;
+}
+
+}  // namespace base64
+
 std::string
 base64Encode(std::uint8_t const* data, std::size_t len);
 

include/xrpl/server/Manifest.h

@@ -1,10 +1,16 @@
 #pragma once
 
 #include <xrpl/basics/UnorderedContainers.h>
+#include <xrpl/basics/base64.h>
+#include <xrpl/basics/base_uint.h>
 #include <xrpl/beast/utility/Journal.h>
 #include <xrpl/protocol/PublicKey.h>
 #include <xrpl/protocol/SecretKey.h>
 
+#include <atomic>
+#include <cstddef>
+#include <cstdint>
+#include <functional>
 #include <optional>
 #include <shared_mutex>
 #include <string>
@@ -35,12 +41,15 @@ namespace xrpl {
     dynamically generates the signatureless form when it needs to verify
     the signature.
 
-    An instance of ManifestCache stores, for each trusted validator, (a) its
+    An instance of ManifestCache stores, for each known validator, (a) its
     master public key, and (b) the most senior of all valid manifests it has
     seen for that validator, if any.  On startup, the [validator_token] config
     entry (which contains the manifest for this validator) is decoded and
     added to the manifest cache.  Other manifests are added as "gossip"
-    received from xrpld peers.
+    received from xrpld peers, including ones for validators this node does not
+    trust. Manifests for untrusted validators are capped (kMaxUntrustedCount)
+    so peer gossip cannot grow the cache without bound; trusted validators are
+    not capped. Entries are never evicted, so a stored revocation is permanent.
 
     When an ephemeral key is compromised, a new signing key pair is created,
     along with a new manifest vouching for it (with a higher sequence number),
@@ -132,6 +141,53 @@ struct Manifest
 std::string
 to_string(Manifest const& m);
 
+/**
+ *Largest a valid manifest can be, in decoded bytes.
+ *
+ *   A manifest has a fixed set of fields. Each is serialized as a field header
+ *   (1-2 bytes), an optional length prefix (1 byte for these sizes), and the
+ *   field body. Taking every field at its largest gives the maximum below, so
+ *   anything larger cannot be a valid manifest.
+ *
+ *       Field                 header + length + body = bytes
+ *       sfVersion   (U16)        2          0     2     4
+ *       sfSequence  (U32)        1          0     4     5
+ *       sfPublicKey (33)         1          1    33    35
+ *       sfSigningPubKey (33)     1          1    33    35
+ *       sfSignature (72)         1          1    72    74
+ *       sfMasterSignature (72)   2          1    72    75
+ *       sfDomain    (128)        1          1   128   130
+ *                                                    -----
+ *                                                      358
+ */
+constexpr std::size_t kMaxManifestBytes = 358;
+
+/**
+ * Largest a valid manifest can be, in base64 characters.
+ *
+ *   base64 encodes 3 bytes as 4 characters, so this is the encoded form of
+ *   @ref kMaxManifestBytes. Callers that receive a base64 manifest should
+ *   reject anything longer than this before decoding, to avoid allocating
+ *   memory for an oversized input.
+ */
+constexpr std::size_t kMaxManifestBase64 = base64::encodedSize(kMaxManifestBytes);
+
+/** Maximum number of manifests carried in a single TMManifests message.
+
+    Outbound, the TMManifests message sent to a peer includes every trusted
+    manifest and fills the rest of this budget with untrusted gossip, so it
+    never exceeds this size. Inbound, trusted manifests are always processed
+    and untrusted ones are processed up to this many, so a peer sending its
+    whole cache cannot force unbounded work.
+
+    The trusted set is tiny relative to this bound, so trusted manifests are
+    not dropped in practice. This is a transitional per-message cap; the cache
+    already bounds untrusted manifests (see kMaxUntrustedCount), so it is no
+    longer needed once the network has upgraded past nodes that send their
+    whole cache in one message.
+*/
+constexpr std::size_t kMaxManifestsPerMessage = 200;
+
 /** Constructs Manifest from serialized string
 
     @param s Serialized manifest string
@@ -206,7 +262,10 @@ enum class ManifestDisposition {
     BadEphemeralKey,
 
     /// Timely, but invalid signature
-    Invalid
+    Invalid,
+
+    /// Unlisted and limit reached
+    UntrustedCapacity
 };
 
 inline std::string
@@ -224,11 +283,25 @@ to_string(ManifestDisposition m)
             return "badEphemeralKey";
         case ManifestDisposition::Invalid:
             return "invalid";
+        case ManifestDisposition::UntrustedCapacity:
+            return "untrustedCapacity";
         default:
             return "unknown";
     }
 }
 
+/**
+ * Whether a manifest counts against the 'untrusted' cache cap.
+ *
+ * Passed to `ManifestCache::applyManifest` with no default, so every caller
+ * must choose. `Capped` is the safe, flood-resistant value; only listed or
+ * configured keys should use `Uncapped`.
+ */
+enum class ManifestRateLimitCapPolicy : std::uint8_t {
+    Capped,   ///< Subject to the untrusted cap (unlisted peer gossip)
+    Uncapped  ///< Bypasses the cap (listed/trusted or config manifests)
+};
+
 class DatabaseCon;
 
 /** Remembers manifests with the highest sequence number. */
@@ -246,6 +319,38 @@ private:
 
     std::atomic<std::uint32_t> seq_{0};
 
+    /**
+     * Master keys of cached manifests for validators this node does not list.
+     *
+     * One entry per capped key in `map_`; its size enforces the cap below.
+     * A key is added when first cached under `Capped` and removed when it
+     * becomes listed (see `promoteToTrusted`) or an `Uncapped` update arrives,
+     * never re-added on de-listing. Uncapped keys are not tracked here.
+     */
+    hash_set<PublicKey> untrustedKeys_;
+
+    /**
+     * Maximum number of untrusted master keys kept in the cache.
+     *
+     * Once reached, a manifest for a brand-new unlisted key is rejected.
+     */
+    static constexpr std::size_t kMaxUntrustedCount = 100;
+
+    /**
+     * Running count of manifests rejected because the untrusted cap was full.
+     *
+     * Drives throttled logging (see `kUntrustedRejectCount`). Atomic because
+     * `applyManifest` may run concurrently.
+     */
+    std::atomic<std::uint64_t> untrustedRejectCount_{0};
+
+    /**
+     * Number of cap rejections between summary warnings.
+     *
+     * @see untrustedRejectCount_
+     */
+    static constexpr std::uint64_t kUntrustedRejectCount = 10000;
+
 public:
     explicit ManifestCache(beast::Journal j = beast::Journal(beast::Journal::getNullSink())) : j_(j)
     {
@@ -321,17 +426,44 @@ public:
 
     /** Add manifest to cache.
 
+        A brand-new unlisted key is rejected once the untrusted cap is full;
+        updates to a cached key and `Uncapped` manifests bypass the cap. The
+        caller decides `cap` before calling so the cache lock is not held while
+        consulting the validator list, which would risk a lock-ordering deadlock.
+
         @param m Manifest to add
 
-        @return `ManifestDisposition::accepted` if successful, or
-                `stale` or `invalid` otherwise
+        @param cap `Uncapped` skips the untrusted cap; use it for keys that are
+               listed, configured, or loaded from the DB. Note `Uncapped` does
+               not assert the key is currently trusted (a DB entry may predate a
+               de-listing). Callers must state this explicitly so a manifest is
+               never left uncapped by omission.
+
+        @return `Accepted` if stored, `Stale` if superseded, `Invalid`/
+                `BadEphemeralKey` if malformed, or `UntrustedCapacity` if the
+                untrusted cap is full.
 
         @par Thread Safety
 
         May be called concurrently
     */
     ManifestDisposition
-    applyManifest(Manifest m);
+    applyManifest(Manifest m, ManifestRateLimitCapPolicy cap);
+
+    /**
+     * Stop counting a master key against the untrusted cap.
+     *
+     * Called when a cached untrusted key becomes listed, freeing its slot.
+     * Idempotent and a no-op for keys that were never counted.
+     *
+     * @param pk Master public key that is now listed/trusted
+     *
+     * @par Thread Safety
+     *
+     * May be called concurrently
+     */
+    void
+    promoteToTrusted(PublicKey const& pk);
 
     /** Populate manifest cache with manifests in database and config.
 

src/libxrpl/basics/base64.cpp

@@ -76,20 +76,6 @@ getInverse()
     return &kTab[0];
 }
 
-/// Returns max chars needed to encode a base64 string
-constexpr std::size_t
-encodedSize(std::size_t n)
-{
-    return 4 * ((n + 2) / 3);
-}
-
-/// Returns max bytes needed to decode a base64 string
-constexpr std::size_t
-decodedSize(std::size_t n)
-{
-    return ((n / 4) * 3) + 2;
-}
-
 /** Encode a series of octets as a padded, base64 string.
 
     The resulting string will not be null terminated.

src/libxrpl/protocol/BuildInfo.cpp

@@ -23,7 +23,7 @@ namespace {
 //------------------------------------------------------------------------------
 // clang-format off
 // NOLINTNEXTLINE(readability-identifier-naming)
-char const* const versionString = "3.2.0"
+char const* const versionString = "3.2.1"
     // clang-format on
     ;
 

src/libxrpl/server/Manifest.cpp

@@ -62,6 +62,11 @@ deserializeManifest(Slice s, beast::Journal journal)
     if (s.empty())
         return std::nullopt;
 
+    // A valid manifest has a fixed maximum size, so reject anything larger
+    // before parsing it.
+    if (s.size() > kMaxManifestBytes)
+        return std::nullopt;
+
     static SOTemplate const kManifestFormat{
         // A manifest must include:
         // - the master public key
@@ -377,16 +382,20 @@ ManifestCache::revoked(PublicKey const& pk) const
 }
 
 ManifestDisposition
-ManifestCache::applyManifest(Manifest m)
+ManifestCache::applyManifest(Manifest m, ManifestRateLimitCapPolicy const cap)
 {
+    bool const uncapped = cap == ManifestRateLimitCapPolicy::Uncapped;
+
+    // The signature is checked only on the first `prewriteCheck` run (under the
+    // read lock). It is expensive, so `checkSignature` is cleared the first
+    // time it is read; the second run (under the write lock) skips it.
+    bool checkSignature = true;
+
     // Check the manifest against the conditions that do not require a
-    // `unique_lock` (write lock) on the `mutex_`. Since the signature can be
-    // relatively expensive, the `checkSignature` parameter determines if the
-    // signature should be checked. Since `prewriteCheck` is run twice (see
-    // comment below), `checkSignature` only needs to be set to true on the
-    // first run.
-    auto prewriteCheck = [this, &m](auto const& iter, bool checkSignature, auto const& lock)
-        -> std::optional<ManifestDisposition> {
+    // `unique_lock` (write lock) on the `mutex_`.
+    auto prewriteCheck = [this, &m, &checkSignature](
+                             auto const& iter,
+                             auto const& lock) -> std::optional<ManifestDisposition> {
         XRPL_ASSERT(lock.owns_lock(), "xrpl::ManifestCache::applyManifest::prewriteCheck : locked");
         (void)lock;  // not used. parameter is present to ensure the mutex is
                      // locked when the lambda is called.
@@ -401,11 +410,15 @@ ManifestCache::applyManifest(Manifest m)
             return ManifestDisposition::Stale;
         }
 
-        if (checkSignature && !m.verify())
+        if (checkSignature)
         {
-            if (auto stream = j_.warn())
-                logMftAct(stream, "Invalid", m.masterKey, m.sequence);
-            return ManifestDisposition::Invalid;
+            checkSignature = false;
+            if (!m.verify())
+            {
+                if (auto stream = j_.warn())
+                    logMftAct(stream, "Invalid", m.masterKey, m.sequence);
+                return ManifestDisposition::Invalid;
+            }
         }
 
         // If the master key associated with a manifest is or might be
@@ -465,14 +478,51 @@ ManifestCache::applyManifest(Manifest m)
         return std::nullopt;
     };
 
+    // Reject a brand-new manifest for an unlisted key once the untrusted cap
+    // is full. Updates to a cached key and uncapped manifests always pass.
+    // Called under both the read and write lock, since the cap can be reached
+    // between the two. The lock param enforces that.
+    auto atUntrustedCap = [this, &m, uncapped](auto const& iter, auto const& lock) {
+        XRPL_ASSERT(
+            lock.owns_lock(), "xrpl::ManifestCache::applyManifest::atUntrustedCap : locked");
+        (void)lock;  // not used. parameter is present to ensure the mutex is
+                     // locked when the lambda is called.
+        if (iter == map_.end() && !uncapped && untrustedKeys_.size() >= kMaxUntrustedCount)
+        {
+            // Log each rejection at debug, but warn only once per interval so a
+            // flood does not fill the log.
+            if (auto stream = j_.debug())
+                logMftAct(stream, "UntrustedCapacity", m.masterKey, m.sequence);
+            if (auto const n = untrustedRejectCount_.fetch_add(1) + 1;
+                n % kUntrustedRejectCount == 0)
+            {
+                JLOG(j_.warn()) << "Untrusted manifest cap reached; " << n
+                                << " manifests rejected so far";
+            }
+            return true;
+        }
+        return false;
+    };
+
     {
         std::shared_lock const sl{mutex_};
-        if (auto d = prewriteCheck(map_.find(m.masterKey), /*checkSig*/ true, sl))
+        auto const iter = map_.find(m.masterKey);
+
+        if (atUntrustedCap(iter, sl))
+            return ManifestDisposition::UntrustedCapacity;
+
+        if (auto d = prewriteCheck(iter, sl); d.has_value())
             return *d;
     }
 
     std::unique_lock const sl{mutex_};
     auto const iter = map_.find(m.masterKey);
+
+    // Re-check the cap under the write lock: the cache may have grown while the
+    // read lock above was released.
+    if (atUntrustedCap(iter, sl))
+        return ManifestDisposition::UntrustedCapacity;
+
     // Since we released the previously held read lock, it's possible that the
     // collections have been written to. This means we need to run
     // `prewriteCheck` again. This re-does work, but `prewriteCheck` is
@@ -482,7 +532,7 @@ ManifestCache::applyManifest(Manifest m)
     // doesn't need to happen again (signature checks are somewhat expensive).
     // Note: It's a mistake to use an upgradable lock. This is a recipe for
     // deadlock.
-    if (auto d = prewriteCheck(iter, /*checkSig*/ false, sl))
+    if (auto d = prewriteCheck(iter, sl); d.has_value())
         return *d;
 
     bool const revoked = m.revoked();
@@ -501,6 +551,12 @@ ManifestCache::applyManifest(Manifest m)
         }
 
         auto masterKey = m.masterKey;
+
+        // Count this key against the untrusted cap. Uncapped keys (listed,
+        // configured, or DB-loaded) are not tracked.
+        if (!uncapped)
+            untrustedKeys_.insert(masterKey);
+
         map_.emplace(std::move(masterKey), std::move(m));
 
         // Something has changed. Keep track of it.
@@ -514,6 +570,11 @@ ManifestCache::applyManifest(Manifest m)
     if (auto stream = j_.info())
         logMftAct(stream, "AcceptedUpdate", m.masterKey, m.sequence, iter->second.sequence);
 
+    // If this key was counted against the cap but now arrives uncapped, free
+    // its slot without waiting for promoteToTrusted.
+    if (uncapped)
+        untrustedKeys_.erase(m.masterKey);
+
     signingToMasterKeys_.erase(
         *iter->second.signingKey);  // NOLINT(bugprone-unchecked-optional-access) prewriteCheck
                                     // ensures old manifest is not revoked
@@ -521,8 +582,8 @@ ManifestCache::applyManifest(Manifest m)
     if (!revoked)
     {
         signingToMasterKeys_.emplace(
-            *m.signingKey, m.masterKey);  // NOLINT(bugprone-unchecked-optional-access) non-revoked
-                                          // manifest always has signingKey
+            *m.signingKey, m.masterKey);  // NOLINT(bugprone-unchecked-optional-access)
+                                          // non-revoked manifest always has signingKey
     }
 
     iter->second = std::move(m);
@@ -533,6 +594,16 @@ ManifestCache::applyManifest(Manifest m)
     return ManifestDisposition::Accepted;
 }
 
+void
+ManifestCache::promoteToTrusted(PublicKey const& pk)
+{
+    // Frees the key's untrusted slot; a no-op (and idempotent) if the key was
+    // never counted. Not re-added on de-listing, so list/de-list cannot grow
+    // the count.
+    std::unique_lock const sl{mutex_};
+    untrustedKeys_.erase(pk);
+}
+
 void
 ManifestCache::load(DatabaseCon& dbCon, std::string const& dbTable)
 {
@@ -563,7 +634,8 @@ ManifestCache::load(
             JLOG(j_.warn()) << "Configured manifest revokes public key";
         }
 
-        if (applyManifest(std::move(*mo)) == ManifestDisposition::Invalid)
+        if (applyManifest(std::move(*mo), ManifestRateLimitCapPolicy::Uncapped) ==
+            ManifestDisposition::Invalid)
         {
             JLOG(j_.error()) << "Manifest in config was rejected";
             return false;
@@ -585,7 +657,9 @@ ManifestCache::load(
 
         auto mo = deserializeManifest(base64Decode(revocationStr));
 
-        if (!mo || !mo->revoked() || applyManifest(std::move(*mo)) == ManifestDisposition::Invalid)
+        if (!mo || !mo->revoked() ||
+            applyManifest(std::move(*mo), ManifestRateLimitCapPolicy::Uncapped) ==
+                ManifestDisposition::Invalid)
         {
             JLOG(j_.error()) << "Invalid validator key revocation in config";
             return false;

src/libxrpl/server/Wallet.cpp

@@ -27,6 +27,7 @@
 #include <soci/use.h>
 
 #include <array>
+#include <cstddef>
 #include <functional>
 #include <memory>
 #include <string>
@@ -75,7 +76,9 @@ getManifests(
                 continue;
             }
 
-            cache.applyManifest(std::move(*mo));
+            // Only trusted manifests are persisted (see saveManifests), so
+            // anything loaded from the DB bypasses the untrusted cap.
+            cache.applyManifest(std::move(*mo), ManifestRateLimitCapPolicy::Uncapped);
         }
         else
         {
@@ -105,19 +108,27 @@ saveManifests(
 {
     soci::transaction tr(session);
     session << "DELETE FROM " << dbTable;
+    // Count skipped untrusted manifests and log one summary afterwards, since
+    // the cache can hold many and per-entry logging would flood at shutdown.
+    std::size_t skipped = 0;
     for (auto const& v : map)
     {
-        // Save all revocation manifests,
-        // but only save trusted non-revocation manifests.
-        if (!v.second.revoked() && !isTrusted(v.second.masterKey))
+        // Persist only trusted keys. Untrusted gossip is left out so a flood
+        // cannot survive a restart on disk.
+        if (!isTrusted(v.second.masterKey))
         {
-            JLOG(j.info()) << "Untrusted manifest in cache not saved to db";
+            ++skipped;
             continue;
         }
 
         saveManifest(session, dbTable, v.second.serialized);
     }
     tr.commit();
+
+    if (skipped != 0)
+    {
+        JLOG(j.info()) << skipped << " untrusted manifest(s) in cache not saved to db";
+    }
 }
 
 void

src/test/app/Manifest_test.cpp

@@ -399,7 +399,8 @@ public:
         BEAST_EXPECT(
             ManifestDisposition::Accepted ==
             cache.applyManifest(
-                makeManifest(sk, KeyType::Ed25519, kp0.second, KeyType::Secp256k1, 0)));
+                makeManifest(sk, KeyType::Ed25519, kp0.second, KeyType::Secp256k1, 0),
+                ManifestRateLimitCapPolicy::Capped));
         BEAST_EXPECT(cache.getSigningKey(pk) == kp0.first);
         BEAST_EXPECT(cache.getMasterKey(kp0.first) == pk);
 
@@ -411,7 +412,8 @@ public:
         BEAST_EXPECT(
             ManifestDisposition::Accepted ==
             cache.applyManifest(
-                makeManifest(sk, KeyType::Ed25519, kp1.second, KeyType::Secp256k1, 1)));
+                makeManifest(sk, KeyType::Ed25519, kp1.second, KeyType::Secp256k1, 1),
+                ManifestRateLimitCapPolicy::Capped));
         BEAST_EXPECT(cache.getSigningKey(pk) == kp1.first);
         BEAST_EXPECT(cache.getMasterKey(kp1.first) == pk);
         BEAST_EXPECT(cache.getMasterKey(kp0.first) == kp0.first);
@@ -421,7 +423,8 @@ public:
         BEAST_EXPECT(
             ManifestDisposition::BadEphemeralKey ==
             cache.applyManifest(
-                makeManifest(sk, KeyType::Ed25519, kp1.second, KeyType::Secp256k1, 2)));
+                makeManifest(sk, KeyType::Ed25519, kp1.second, KeyType::Secp256k1, 2),
+                ManifestRateLimitCapPolicy::Capped));
         BEAST_EXPECT(cache.getSigningKey(pk) == kp1.first);
         BEAST_EXPECT(cache.getMasterKey(kp1.first) == pk);
         BEAST_EXPECT(cache.getMasterKey(kp0.first) == kp0.first);
@@ -431,7 +434,8 @@ public:
         // key from a revoked master public key
         BEAST_EXPECT(
             ManifestDisposition::Accepted ==
-            cache.applyManifest(makeRevocation(sk, KeyType::Ed25519)));
+            cache.applyManifest(
+                makeRevocation(sk, KeyType::Ed25519), ManifestRateLimitCapPolicy::Capped));
         BEAST_EXPECT(cache.revoked(pk));
         BEAST_EXPECT(cache.getSigningKey(pk) == pk);
         BEAST_EXPECT(cache.getMasterKey(kp0.first) == kp0.first);
@@ -902,39 +906,69 @@ public:
             // applyManifest should accept new manifests with
             // higher sequence numbers
             auto const seq0 = cache.sequence();
-            BEAST_EXPECT(cache.applyManifest(clone(sA0)) == ManifestDisposition::Accepted);
+            BEAST_EXPECT(
+                cache.applyManifest(clone(sA0), ManifestRateLimitCapPolicy::Capped) ==
+                ManifestDisposition::Accepted);
             BEAST_EXPECT(cache.sequence() > seq0);
 
             auto const seq1 = cache.sequence();
-            BEAST_EXPECT(cache.applyManifest(clone(sA0)) == ManifestDisposition::Stale);
+            BEAST_EXPECT(
+                cache.applyManifest(clone(sA0), ManifestRateLimitCapPolicy::Capped) ==
+                ManifestDisposition::Stale);
             BEAST_EXPECT(cache.sequence() == seq1);
 
-            BEAST_EXPECT(cache.applyManifest(clone(sA1)) == ManifestDisposition::Accepted);
-            BEAST_EXPECT(cache.applyManifest(clone(sA1)) == ManifestDisposition::Stale);
-            BEAST_EXPECT(cache.applyManifest(clone(sA0)) == ManifestDisposition::Stale);
+            BEAST_EXPECT(
+                cache.applyManifest(clone(sA1), ManifestRateLimitCapPolicy::Capped) ==
+                ManifestDisposition::Accepted);
+            BEAST_EXPECT(
+                cache.applyManifest(clone(sA1), ManifestRateLimitCapPolicy::Capped) ==
+                ManifestDisposition::Stale);
+            BEAST_EXPECT(
+                cache.applyManifest(clone(sA0), ManifestRateLimitCapPolicy::Capped) ==
+                ManifestDisposition::Stale);
 
-            BEAST_EXPECT(cache.applyManifest(clone(sA2)) == ManifestDisposition::BadEphemeralKey);
+            BEAST_EXPECT(
+                cache.applyManifest(clone(sA2), ManifestRateLimitCapPolicy::Capped) ==
+                ManifestDisposition::BadEphemeralKey);
 
             // applyManifest should accept manifests with max sequence numbers
             // that revoke the master public key
             BEAST_EXPECT(!cache.revoked(pkA));
             BEAST_EXPECT(sAMax.revoked());
-            BEAST_EXPECT(cache.applyManifest(clone(sAMax)) == ManifestDisposition::Accepted);
-            BEAST_EXPECT(cache.applyManifest(clone(sAMax)) == ManifestDisposition::Stale);
-            BEAST_EXPECT(cache.applyManifest(clone(sA1)) == ManifestDisposition::Stale);
-            BEAST_EXPECT(cache.applyManifest(clone(sA0)) == ManifestDisposition::Stale);
+            BEAST_EXPECT(
+                cache.applyManifest(clone(sAMax), ManifestRateLimitCapPolicy::Capped) ==
+                ManifestDisposition::Accepted);
+            BEAST_EXPECT(
+                cache.applyManifest(clone(sAMax), ManifestRateLimitCapPolicy::Capped) ==
+                ManifestDisposition::Stale);
+            BEAST_EXPECT(
+                cache.applyManifest(clone(sA1), ManifestRateLimitCapPolicy::Capped) ==
+                ManifestDisposition::Stale);
+            BEAST_EXPECT(
+                cache.applyManifest(clone(sA0), ManifestRateLimitCapPolicy::Capped) ==
+                ManifestDisposition::Stale);
             BEAST_EXPECT(cache.revoked(pkA));
 
             // applyManifest should reject manifests with invalid signatures
-            BEAST_EXPECT(cache.applyManifest(clone(sB0)) == ManifestDisposition::Accepted);
-            BEAST_EXPECT(cache.applyManifest(clone(sB0)) == ManifestDisposition::Stale);
+            BEAST_EXPECT(
+                cache.applyManifest(clone(sB0), ManifestRateLimitCapPolicy::Capped) ==
+                ManifestDisposition::Accepted);
+            BEAST_EXPECT(
+                cache.applyManifest(clone(sB0), ManifestRateLimitCapPolicy::Capped) ==
+                ManifestDisposition::Stale);
             BEAST_EXPECT(!deserializeManifest(fake));
-            BEAST_EXPECT(cache.applyManifest(clone(sB1)) == ManifestDisposition::Invalid);
-            BEAST_EXPECT(cache.applyManifest(clone(sB2)) == ManifestDisposition::Accepted);
+            BEAST_EXPECT(
+                cache.applyManifest(clone(sB1), ManifestRateLimitCapPolicy::Capped) ==
+                ManifestDisposition::Invalid);
+            BEAST_EXPECT(
+                cache.applyManifest(clone(sB2), ManifestRateLimitCapPolicy::Capped) ==
+                ManifestDisposition::Accepted);
 
             auto const sC0 = makeManifest(
                 kpB2.second, KeyType::Ed25519, randomSecretKey(), KeyType::Ed25519, 47);
-            BEAST_EXPECT(cache.applyManifest(clone(sC0)) == ManifestDisposition::BadMasterKey);
+            BEAST_EXPECT(
+                cache.applyManifest(clone(sC0), ManifestRateLimitCapPolicy::Capped) ==
+                ManifestDisposition::BadMasterKey);
         }
 
         testLoadStore(cache);

src/test/app/ValidatorList_test.cpp

@@ -277,8 +277,10 @@ private:
                 trustedKeys->load(localSigningPublicOuter, emptyCfgKeys, emptyCfgPublishers));
             BEAST_EXPECT(trustedKeys->listed(localSigningPublicOuter));
 
-            // NOLINTNEXTLINE(bugprone-unchecked-optional-access)
-            manifests.applyManifest(*deserializeManifest(cfgManifest));
+            // NOLINTBEGIN(bugprone-unchecked-optional-access)
+            manifests.applyManifest(
+                *deserializeManifest(cfgManifest), ManifestRateLimitCapPolicy::Capped);
+            // NOLINTEND(bugprone-unchecked-optional-access)
             BEAST_EXPECT(
                 trustedKeys->load(localSigningPublicOuter, emptyCfgKeys, emptyCfgPublishers));
 
@@ -368,8 +370,10 @@ private:
                 app.config().legacy("database_path"),
                 env.journal);
 
-            // NOLINTNEXTLINE(bugprone-unchecked-optional-access)
-            manifests.applyManifest(*deserializeManifest(cfgManifest));
+            // NOLINTBEGIN(bugprone-unchecked-optional-access)
+            manifests.applyManifest(
+                *deserializeManifest(cfgManifest), ManifestRateLimitCapPolicy::Capped);
+            // NOLINTEND(bugprone-unchecked-optional-access)
 
             BEAST_EXPECT(trustedKeys->load(localSigningPublicOuter, cfgKeys, emptyCfgPublishers));
 
@@ -454,13 +458,16 @@ private:
             auto const pubRevokedSigning = randomKeyPair(KeyType::Secp256k1);
             // make this manifest revoked (seq num = max)
             //  -- thus should not be loaded
-            // NOLINTNEXTLINE(bugprone-unchecked-optional-access)
-            pubManifests.applyManifest(*deserializeManifest(makeManifestString(
-                pubRevokedPublic,
-                pubRevokedSecret,
-                pubRevokedSigning.first,
-                pubRevokedSigning.second,
-                std::numeric_limits<std::uint32_t>::max())));
+            // NOLINTBEGIN(bugprone-unchecked-optional-access)
+            pubManifests.applyManifest(
+                *deserializeManifest(makeManifestString(
+                    pubRevokedPublic,
+                    pubRevokedSecret,
+                    pubRevokedSigning.first,
+                    pubRevokedSigning.second,
+                    std::numeric_limits<std::uint32_t>::max())),
+                ManifestRateLimitCapPolicy::Capped);
+            // NOLINTEND(bugprone-unchecked-optional-access)
 
             // these two are not revoked (and not in the manifest cache at all.)
             auto legitKey1 = randomMasterKey();
@@ -493,13 +500,16 @@ private:
             auto const pubRevokedSigning = randomKeyPair(KeyType::Secp256k1);
             // make this manifest revoked (seq num = max)
             //  -- thus should not be loaded
-            // NOLINTNEXTLINE(bugprone-unchecked-optional-access)
-            pubManifests.applyManifest(*deserializeManifest(makeManifestString(
-                pubRevokedPublic,
-                pubRevokedSecret,
-                pubRevokedSigning.first,
-                pubRevokedSigning.second,
-                std::numeric_limits<std::uint32_t>::max())));
+            // NOLINTBEGIN(bugprone-unchecked-optional-access)
+            pubManifests.applyManifest(
+                *deserializeManifest(makeManifestString(
+                    pubRevokedPublic,
+                    pubRevokedSecret,
+                    pubRevokedSigning.first,
+                    pubRevokedSigning.second,
+                    std::numeric_limits<std::uint32_t>::max())),
+                ManifestRateLimitCapPolicy::Capped);
+            // NOLINTEND(bugprone-unchecked-optional-access)
 
             // this one is not revoked (and not in the manifest cache at all.)
             auto legitKey = randomMasterKey();
@@ -1164,7 +1174,8 @@ private:
 
             BEAST_EXPECT(
                 // NOLINTNEXTLINE(bugprone-unchecked-optional-access)
-                manifestsOuter.applyManifest(std::move(*m1)) == ManifestDisposition::Accepted);
+                manifestsOuter.applyManifest(std::move(*m1), ManifestRateLimitCapPolicy::Capped) ==
+                ManifestDisposition::Accepted);
             BEAST_EXPECT(trustedKeysOuter->listed(masterPublic));
             BEAST_EXPECT(trustedKeysOuter->trusted(masterPublic));
             BEAST_EXPECT(trustedKeysOuter->listed(signingPublic1));
@@ -1178,7 +1189,8 @@ private:
                 masterPublic, masterPrivate, signingPublic2, signingKeys2.second, 2));
             BEAST_EXPECT(
                 // NOLINTNEXTLINE(bugprone-unchecked-optional-access)
-                manifestsOuter.applyManifest(std::move(*m2)) == ManifestDisposition::Accepted);
+                manifestsOuter.applyManifest(std::move(*m2), ManifestRateLimitCapPolicy::Capped) ==
+                ManifestDisposition::Accepted);
             BEAST_EXPECT(trustedKeysOuter->listed(masterPublic));
             BEAST_EXPECT(trustedKeysOuter->trusted(masterPublic));
             BEAST_EXPECT(trustedKeysOuter->listed(signingPublic2));
@@ -1195,7 +1207,8 @@ private:
             // NOLINTBEGIN(bugprone-unchecked-optional-access)
             BEAST_EXPECT(max->revoked());
             BEAST_EXPECT(
-                manifestsOuter.applyManifest(std::move(*max)) == ManifestDisposition::Accepted);
+                manifestsOuter.applyManifest(std::move(*max), ManifestRateLimitCapPolicy::Capped) ==
+                ManifestDisposition::Accepted);
             // NOLINTEND(bugprone-unchecked-optional-access)
 
             BEAST_EXPECT(manifestsOuter.getSigningKey(masterPublic) == masterPublic);
@@ -2612,7 +2625,9 @@ private:
             auto threshold = listThreshold > 0 ? std::optional(listThreshold) : std::nullopt;
             if (self)
             {
-                valManifests.applyManifest(*deserializeManifest(base64Decode(self->manifest)));
+                valManifests.applyManifest(
+                    *deserializeManifest(base64Decode(self->manifest)),
+                    ManifestRateLimitCapPolicy::Capped);
                 BEAST_EXPECT(
                     result->load(self->signingPublic, emptyCfgKeys, cfgPublishers, threshold));
             }

src/xrpld/app/misc/detail/ValidatorList.cpp

@@ -1065,6 +1065,8 @@ ValidatorList::updatePublisherList(
         {
             // Increment list count for added keys
             ++keyListings_[*iNew];
+            // Key is now listed: free its untrusted slot if it had one.
+            validatorManifests_.promoteToTrusted(*iNew);
             ++iNew;
         }
         else if (iNew == publisherList.end() || (iOld != oldList.end() && *iOld < *iNew))
@@ -1103,7 +1105,8 @@ ValidatorList::updatePublisherList(
             continue;
         }
 
-        if (auto const r = validatorManifests_.applyManifest(std::move(*m));
+        if (auto const r = validatorManifests_.applyManifest(
+                std::move(*m), ManifestRateLimitCapPolicy::Uncapped);
             r == ManifestDisposition::Invalid)
         {
             JLOG(j_.warn()) << "List for " << strHex(pubKey)
@@ -1127,6 +1130,15 @@ ValidatorList::applyList(
 
     json::Value list;
     auto const& manifest = localManifest ? *localManifest : globalManifest;
+    // Reject an oversized manifest before decoding it, so we do not allocate
+    // memory for an input that cannot be a valid manifest. deserializeManifest
+    // also enforces the decoded-byte limit, but checking here avoids the
+    // base64 decode entirely.
+    if (manifest.size() > kMaxManifestBase64)
+    {
+        JLOG(j_.warn()) << "UNL manifest exceeds maximum size";
+        return PublisherListStats{ListDisposition::Invalid};
+    }
     auto m = deserializeManifest(base64Decode(manifest));
     if (!m)
     {
@@ -1348,7 +1360,10 @@ ValidatorList::verify(
     PublicKey masterPubKey = manifest.masterKey;
     auto const revoked = manifest.revoked();
 
-    auto const result = publisherManifests_.applyManifest(std::move(manifest));
+    // Publisher keys are configured/trusted (checked above), so bypass the
+    // untrusted cap.
+    auto const result = publisherManifests_.applyManifest(
+        std::move(manifest), ManifestRateLimitCapPolicy::Uncapped);
 
     if (revoked && result == ManifestDisposition::Accepted)
     {

src/xrpld/overlay/Message.h

@@ -5,6 +5,7 @@
 #include <xrpl/basics/ByteUtilities.h>
 #include <xrpl/protocol/PublicKey.h>
 #include <xrpl/protocol/messages.h>
+#include <xrpl/server/Manifest.h>
 
 #include <algorithm>
 #include <cstdint>
@@ -13,6 +14,13 @@ namespace xrpl {
 
 constexpr std::size_t kMaximumMessageSize = megabytes(64);
 
+// Upper bound on the wire size of a TMManifests message: kMaxManifestsPerMessage entries
+// of at most kMaxManifestBytes each, plus a small allowance for protobuf
+// framing per entry.
+constexpr std::size_t kManifestFramingBytes = 8;
+constexpr std::size_t kMaximumManifestsMessageSize =
+    kMaxManifestsPerMessage * (kMaxManifestBytes + kManifestFramingBytes);
+
 // VFALCO NOTE If we forward declare Message and write out shared_ptr
 //             instead of using the in-class type alias, we can remove the
 //             entire ripple.pb.h from the main headers.

src/xrpld/overlay/detail/OverlayImpl.cpp

@@ -43,6 +43,7 @@
 #include <xrpl/protocol/Serializer.h>
 #include <xrpl/protocol/SystemParameters.h>
 #include <xrpl/protocol/jss.h>
+#include <xrpl/resource/Fees.h>
 #include <xrpl/resource/ResourceManager.h>
 #include <xrpl/server/Handoff.h>
 #include <xrpl/server/Manifest.h>
@@ -661,25 +662,53 @@ OverlayImpl::onManifests(
     std::shared_ptr<protocol::TMManifests> const& m,
     std::shared_ptr<PeerImp> const& from)
 {
-    auto const n = m->list_size();
     auto const& journal = from->pJournal();
 
+    // Process every trusted manifest, but stop processing untrusted ones once
+    // kMaxManifestsPerMessage of them have been handled, so the work stays bounded.
+    auto const total = static_cast<std::size_t>(m->list_size());
+    std::size_t untrusted = 0;
+    bool skippedUntrusted = false;
+
     protocol::TMManifests relay;
 
-    for (std::size_t i = 0; i < n; ++i)
+    for (std::size_t i = 0; i < total; ++i)
     {
         auto& s = m->list().Get(i).stobject();
 
         if (auto mo = deserializeManifest(s))
         {
             auto const serialized = mo->serialized;
+            // Resolve trust before applyManifest takes the manifest-cache
+            // lock: listed() takes the validator-list lock, so ordering it
+            // first avoids holding the two locks in opposite orders.
+            bool const isTrusted = app_.getValidators().listed(mo->masterKey);
 
-            auto const result = app_.getValidatorManifests().applyManifest(std::move(*mo));
+            // Bound untrusted work: process at most kMaxManifestsPerMessage
+            // untrusted manifests, but never skip a trusted one. Trusted
+            // manifests are not counted against the cap.
+            if (!isTrusted)
+            {
+                if (untrusted >= kMaxManifestsPerMessage)
+                {
+                    skippedUntrusted = true;
+                    continue;
+                }
+                ++untrusted;
+            }
+            // Updates to a known key are relayed even when untrusted. Use
+            // getSequence, not getManifest, to avoid copying the cached payload
+            // on this hot path.
+            bool const isKnown =
+                app_.getValidatorManifests().getSequence(mo->masterKey).has_value();
+
+            auto const result = app_.getValidatorManifests().applyManifest(
+                std::move(*mo),
+                isTrusted ? ManifestRateLimitCapPolicy::Uncapped
+                          : ManifestRateLimitCapPolicy::Capped);
 
             if (result == ManifestDisposition::Accepted)
             {
-                relay.add_list()->set_stobject(s);
-
                 // N.B.: this is important; the applyManifest call above moves
                 //       the loaded Manifest out of the optional so we need to
                 //       reload it here.
@@ -691,10 +720,19 @@ OverlayImpl::onManifests(
                 // NOLINTBEGIN(bugprone-unchecked-optional-access) assert above
                 app_.getOPs().pubManifest(*mo);
 
-                if (app_.getValidators().listed(mo->masterKey))
+                // Relay only trusted manifests or updates to known keys, so
+                // untrusted gossip for a brand-new key cannot be amplified.
+                // Persist to the wallet DB only for trusted keys, so untrusted
+                // gossip never survives a restart.
+                if (isTrusted || isKnown)
                 {
-                    auto db = app_.getWalletDB().checkoutDb();
-                    addValidatorManifest(*db, serialized);
+                    relay.add_list()->set_stobject(s);
+
+                    if (isTrusted)
+                    {
+                        auto db = app_.getWalletDB().checkoutDb();
+                        addValidatorManifest(*db, serialized);
+                    }
                 }
                 // NOLINTEND(bugprone-unchecked-optional-access)
             }
@@ -706,6 +744,18 @@ OverlayImpl::onManifests(
         }
     }
 
+    if (skippedUntrusted)
+    {
+        // The sender exceeded the untrusted per-message cap. Charge it (once,
+        // here) so a flood of untrusted manifests is penalized, while an honest
+        // message of trusted manifests never is.
+        from->charge(Resource::kFeeMalformedRequest, "too many untrusted manifests");
+
+        JLOG(journal.warn()) << "Manifests: message had " << total
+                             << " entries; processed all trusted plus the first "
+                             << kMaxManifestsPerMessage << " untrusted";
+    }
+
     if (!relay.list().empty())
     {
         forEach([m2 = std::make_shared<Message>(relay, protocol::mtMANIFESTS)](
@@ -1207,15 +1257,60 @@ OverlayImpl::getManifestsMessage()
 
     if (auto seq = app_.getValidatorManifests().sequence(); seq != manifestListSeq_)
     {
-        protocol::TMManifests tm;
-
+        // Phase 1: snapshot the cache under its own lock. Do not call
+        // Validators::listed() here — that takes the validator-list lock, and
+        // forEachManifest holds the manifest-cache lock, so consulting trust
+        // inside the callback would invert the lock order used elsewhere
+        // (see onManifests) and risk deadlock. Capture the manifest hash now,
+        // while we have the Manifest object, for the suppression key.
+        struct CachedManifest
+        {
+            PublicKey masterKey;
+            std::string serialized;
+            uint256 hash;
+        };
+        std::vector<CachedManifest> cached;
         app_.getValidatorManifests().forEachManifest(
-            [&tm](std::size_t s) { tm.mutable_list()->Reserve(s); },
-            [&tm, &hr = app_.getHashRouter()](Manifest const& manifest) {
-                tm.add_list()->set_stobject(manifest.serialized.data(), manifest.serialized.size());
-                hr.addSuppression(manifest.hash());
+            [&cached](std::size_t s) { cached.reserve(s); },
+            [&cached](Manifest const& manifest) {
+                cached.push_back({manifest.masterKey, manifest.serialized, manifest.hash()});
             });
 
+        // Phase 2: no cache lock held, so trust checks are safe. Include every
+        // trusted manifest, then fill any remaining headroom up to
+        // kMaxManifestsPerMessage with untrusted gossip, so the whole message
+        // stays within the per-message cap the receiver enforces (trusted
+        // count is tiny in practice, so this effectively never drops trusted).
+        std::vector<CachedManifest const*> selected;
+        std::vector<CachedManifest const*> untrusted;
+        for (auto const& e : cached)
+        {
+            if (app_.getValidators().listed(e.masterKey))
+            {
+                selected.push_back(&e);
+            }
+            else
+            {
+                untrusted.push_back(&e);
+            }
+        }
+
+        // Cap untrusted only; trusted manifests are all included above.
+        auto const take = std::min(kMaxManifestsPerMessage, untrusted.size());
+        selected.insert(selected.end(), untrusted.begin(), untrusted.begin() + take);
+
+        // Shuffle the order. Cryptographic randomness is not needed here.
+        std::shuffle(selected.begin(), selected.end(), defaultPrng());
+
+        protocol::TMManifests tm;
+        auto& hr = app_.getHashRouter();
+        tm.mutable_list()->Reserve(static_cast<int>(selected.size()));
+        for (auto const* e : selected)
+        {
+            tm.add_list()->set_stobject(e->serialized.data(), e->serialized.size());
+            hr.addSuppression(e->hash);
+        }
+
         manifestMessage_.reset();
 
         if (tm.list_size() != 0)

src/xrpld/overlay/detail/PeerImp.cpp

@@ -61,6 +61,7 @@
 #include <xrpl/resource/Gossip.h>
 #include <xrpl/server/Handoff.h>
 #include <xrpl/server/LoadFeeTrack.h>
+#include <xrpl/server/Manifest.h>
 #include <xrpl/server/NetworkOPs.h>
 #include <xrpl/shamap/SHAMapNodeID.h>
 #include <xrpl/tx/apply.h>
@@ -1131,6 +1132,9 @@ PeerImp::onMessage(std::shared_ptr<protocol::TMManifests> const& m)
     if (s > 100)
         fee_.update(Resource::kFeeModerateBurdenPeer, "oversize");
 
+    // OverlayImpl::onManifests bounds the untrusted work and charges the fee
+    // if the untrusted count exceeds the per-message cap; trusted manifests
+    // are always processed and not counted against it.
     app_.getJobQueue().addJob(JtManifest, "RcvManifests", [this, that = shared_from_this(), m]() {
         overlay_.onManifests(m, that);
     });

src/xrpld/overlay/detail/ProtocolMessage.h

@@ -351,6 +351,16 @@ invokeProtocolMessage(Buffers const& buffers, Handler& handler, std::size_t& hin
         return result;
     }
 
+    // Drop an oversized TMManifests without penalty: consume the bytes and
+    // return no error, so the connection is preserved.
+    if (header->messageType == protocol::mtMANIFESTS &&
+        (header->payloadWireSize > kMaximumManifestsMessageSize ||
+         header->uncompressedSize > kMaximumManifestsMessageSize))
+    {
+        result.first = header->totalWireSize;
+        return result;
+    }
+
     bool success = false;
 
     switch (header->messageType)