fix: Check network ID in transactionSignFor (#7102)

include/xrpl/basics/Expected.h

@@ -148,17 +148,23 @@ public:
     }
 
     [[nodiscard]] constexpr E const&
-    error() const
+    error() const&
     {
         return Base::error();
     }
 
-    constexpr E&
-    error()
+    [[nodiscard]] constexpr E&
+    error() &
     {
         return Base::error();
     }
 
+    [[nodiscard]] constexpr E&&
+    error() &&
+    {
+        return std::move(Base::error());
+    }
+
     constexpr explicit
     operator bool() const
     {
@@ -215,17 +221,23 @@ public:
     }
 
     [[nodiscard]] constexpr E const&
-    error() const
+    error() const&
     {
         return Base::error();
     }
 
-    constexpr E&
-    error()
+    [[nodiscard]] constexpr E&
+    error() &
     {
         return Base::error();
     }
 
+    [[nodiscard]] constexpr E&&
+    error() &&
+    {
+        return std::move(Base::error());
+    }
+
     constexpr explicit
     operator bool() const
     {

src/xrpld/rpc/detail/TransactionSign.cpp

@@ -14,6 +14,7 @@
 
 #include <xrpl/basics/Blob.h>
 #include <xrpl/basics/Buffer.h>
+#include <xrpl/basics/Expected.h>
 #include <xrpl/basics/Log.h>
 #include <xrpl/basics/Number.h>
 #include <xrpl/basics/Slice.h>
@@ -54,6 +55,7 @@
 
 #include <algorithm>
 #include <chrono>
+#include <cstdint>
 #include <exception>
 #include <functional>
 #include <memory>
@@ -405,6 +407,25 @@ checkTxJsonFields(
     return ret;
 }
 
+static Expected<void, json::Value>
+checkNetworkID(json::Value const& txJson, uint32_t appNetworkId)
+{
+    if (appNetworkId > 1024)
+    {
+        if (!txJson.isMember(jss::NetworkID))
+        {
+            return Unexpected(
+                RPC::makeError(RpcInvalidParams, RPC::missingFieldMessage("tx_json.NetworkID")));
+        }
+        if (!txJson[jss::NetworkID].isIntegral() || txJson[jss::NetworkID].asUInt() != appNetworkId)
+        {
+            return Unexpected(
+                RPC::makeError(RpcInvalidParams, RPC::invalidFieldMessage("tx_json.NetworkID")));
+        }
+    }
+    return Expected<void, json::Value>();
+}
+
 //------------------------------------------------------------------------------
 
 // A move-only struct that makes it easy to return either a json::Value or a
@@ -1165,8 +1186,16 @@ transactionSignFor(
         if (!txJson.isObject())
             return RPC::objectFieldError(jss::tx_json);
 
-        // If the tx_json.SigningPubKey field is missing,
-        // insert an empty one.
+        if (auto checkResult =
+                detail::checkNetworkID(txJson, app.getNetworkIDService().getNetworkID());
+            !checkResult)
+        {
+            return std::move(checkResult).error();
+        }
+
+        // If the tx_json.SigningPubKey field is missing, insert an empty one,
+        // in order for the `checkMultiSignFields` to not return an error
+        // for non-multisign transactions.
         if (!txJson.isMember(sfSigningPubKey.getJsonName()))
             txJson[sfSigningPubKey.getJsonName()] = "";
     }