diff --git a/CHANGELOG.md b/CHANGELOG.md
index 34f1b9df98c0..0d78c9aad7d1 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -5,6 +5,14 @@ All notable changes to this project will be documented in this file.
 The format is based on [Keep a Changelog](http://keepachangelog.com/en/1.0.0/)
 and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.html).
 
+## [4.0.14]
+
+[4.0.14]: https://github.com/microsoft/CCF/releases/tag/ccf-4.0.14
+
+### Fixed
+
+- Nodes are now more robust to unexpected traffic on node-to-node ports (#5889).
+
 ## [4.0.13]
 
 [4.0.13]: https://github.com/microsoft/CCF/releases/tag/ccf-4.0.13
diff --git a/src/enclave/enclave.h b/src/enclave/enclave.h
index 2e763794a528..8b4ea0503bfe 100644
--- a/src/enclave/enclave.h
+++ b/src/enclave/enclave.h
@@ -350,7 +350,15 @@ namespace ccf
 
         DISPATCHER_SET_MESSAGE_HANDLER(
           bp, ccf::node_inbound, [this](const uint8_t* data, size_t size) {
-            node->recv_node_inbound(data, size);
+            try
+            {
+              node->recv_node_inbound(data, size);
+            }
+            catch (const std::exception& e)
+            {
+              LOG_DEBUG_FMT(
+                "Ignoring node_inbound message due to exception: {}", e.what());
+            }
           });
 
         DISPATCHER_SET_MESSAGE_HANDLER(
diff --git a/src/host/node_connections.h b/src/host/node_connections.h
index 958cf40f73c7..594957b5bbc3 100644
--- a/src/host/node_connections.h
+++ b/src/host/node_connections.h
@@ -35,7 +35,7 @@ namespace asynchost
         node(node)
       {}
 
-      void on_read(size_t len, uint8_t*& incoming, sockaddr)
+      bool on_read(size_t len, uint8_t*& incoming, sockaddr) override
       {
         LOG_DEBUG_FMT(
           "from node {} received {} bytes",
@@ -71,8 +71,35 @@ namespace asynchost
           }
 
           const auto size_pre_headers = size;
-          auto msg_type = serialized::read<ccf::NodeMsgType>(data, size);
-          ccf::NodeId from = serialized::read<ccf::NodeId::Value>(data, size);
+
+          ccf::NodeMsgType msg_type;
+          try
+          {
+            msg_type = serialized::read<ccf::NodeMsgType>(data, size);
+          }
+          catch (const std::exception& e)
+          {
+            LOG_DEBUG_FMT(
+              "Received invalid node-to-node traffic. Unable to read message "
+              "type ({}). Closing connection.",
+              e.what());
+            return false;
+          }
+
+          ccf::NodeId from;
+          try
+          {
+            from = serialized::read<ccf::NodeId::Value>(data, size);
+          }
+          catch (const std::exception& e)
+          {
+            LOG_DEBUG_FMT(
+              "Received invalid node-to-node traffic. Unable to read sender "
+              "node ID ({}). Closing connection.",
+              e.what());
+            return false;
+          }
+
           const auto size_post_headers = size;
           const size_t payload_size =
             msg_size.value() - (size_pre_headers - size_post_headers);
@@ -107,6 +134,8 @@ namespace asynchost
         {
           pending.erase(pending.begin(), pending.begin() + used);
         }
+
+        return true;
       }
 
       virtual void associate_incoming(const ccf::NodeId&) {}
diff --git a/src/host/rpc_connections.h b/src/host/rpc_connections.h
index 7c8e588e608f..e9f41fca8ee9 100644
--- a/src/host/rpc_connections.h
+++ b/src/host/rpc_connections.h
@@ -116,7 +116,7 @@ namespace asynchost
         cleanup();
       }
 
-      void on_read(size_t len, uint8_t*& data, sockaddr) override
+      bool on_read(size_t len, uint8_t*& data, sockaddr) override
       {
         LOG_DEBUG_FMT("rpc read {}: {}", id, len);
 
@@ -125,6 +125,8 @@ namespace asynchost
           parent.to_enclave,
           id,
           serializer::ByteRange{data, len});
+
+        return true;
       }
 
       void on_disconnect() override
@@ -195,7 +197,7 @@ namespace asynchost
         }
       }
 
-      void on_read(size_t len, uint8_t*& data, sockaddr addr) override
+      bool on_read(size_t len, uint8_t*& data, sockaddr addr) override
       {
         // UDP connections don't have clients, it's all done in the server
         if constexpr (isUDP<ConnType>())
@@ -211,6 +213,8 @@ namespace asynchost
             addr_data,
             serializer::ByteRange{data, len});
         }
+
+        return true;
       }
 
       void cleanup()
diff --git a/src/host/socket.h b/src/host/socket.h
index ce1d7e99acb0..5c3bc2d56a24 100644
--- a/src/host/socket.h
+++ b/src/host/socket.h
@@ -30,7 +30,11 @@ namespace asynchost
     virtual ~SocketBehaviour() {}
 
     /// To be implemented by clients
-    virtual void on_read(size_t, uint8_t*&, sockaddr) {}
+    /// Return false to immediately disconnect socket.
+    virtual bool on_read(size_t, uint8_t*&, sockaddr)
+    {
+      return true;
+    }
 
     /// To be implemented by servers with connections
     virtual void on_accept(ConnType&) {}
diff --git a/src/host/tcp.h b/src/host/tcp.h
index 7b2f51a1d6a5..18cf169dcafc 100644
--- a/src/host/tcp.h
+++ b/src/host/tcp.h
@@ -789,12 +789,18 @@ namespace asynchost
       }
 
       uint8_t* p = (uint8_t*)buf->base;
-      behaviour->on_read((size_t)sz, p, {});
+      const bool read_good = behaviour->on_read((size_t)sz, p, {});
 
       if (p != nullptr)
       {
         on_free(buf);
       }
+
+      if (!read_good)
+      {
+        behaviour->on_disconnect();
+        return;
+      }
     }
 
     static void on_write(uv_write_t* req, int)
diff --git a/tests/connections.py b/tests/connections.py
index 5560715effb5..ffeed6911d38 100644
--- a/tests/connections.py
+++ b/tests/connections.py
@@ -16,6 +16,8 @@
 import functools
 import httpx
 import os
+import socket
+import struct
 from infra.snp import IS_SNP
 
 from loguru import logger as LOG
@@ -51,7 +53,7 @@ def interface_caps(i):
     }
 
 
-def run(args):
+def run_connection_caps_tests(args):
     # Listen on additional RPC interfaces with even lower session caps
     for i, node_spec in enumerate(args.nodes):
         caps = interface_caps(i)
@@ -262,14 +264,118 @@ def create_connections_until_exhaustion(
             LOG.warning("Expected a fatal crash and saw none!")
 
 
+@contextlib.contextmanager
+def node_tcp_socket(node):
+    interface = node.n2n_interface
+    s = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
+    s.connect((interface.host, interface.port))
+    yield s
+    s.close()
+
+
+def run_node_socket_robustness_tests(args):
+    with infra.network.network(
+        args.nodes, args.binary_dir, args.debug_nodes, args.perf_nodes, pdb=args.pdb
+    ) as network:
+        network.start_and_open(args)
+
+        primary, _ = network.find_nodes()
+
+        # Protocol is:
+        # - 4 byte message size N (remainder is not processed until this many bytes arrive)
+        # - 8 byte message type (valid values are only 0, 1, or 2)
+        # - Sender node ID (length-prefixed string), consisting of:
+        #   - 8 byte string length S
+        #   - S bytes of string content
+        # - Message body, of N - 16 - S bytes
+        # Note number serialization is little-endian!
+
+        def encode_msg(
+            msg_type=0,
+            sender="OtherNode",
+            body=b"",
+            sender_len_override=None,
+            total_len_override=None,
+        ):
+            b_type = struct.pack("<Q", msg_type)
+            sender_len = sender_len_override or len(sender)
+            b_sender = struct.pack("<Q", sender_len) + sender.encode()
+            total_len = total_len_override or len(b_type) + len(b_sender) + len(body)
+            b_size = struct.pack("<I", total_len)
+            encoded_msg = b_size + b_type + b_sender + body
+            return encoded_msg
+
+        def try_write(msg_bytes):
+            with node_tcp_socket(primary) as sock:
+                LOG.debug(
+                    f"Sending raw TCP bytes to {primary.local_node_id}'s node-to-node port: {msg_bytes}"
+                )
+                sock.send(msg_bytes)
+                assert (
+                    not primary.remote.check_done()
+                ), f"Crashed node with N2N message: {msg_bytes}"
+                LOG.success(f"Node {primary.local_node_id} tolerated this message")
+
+        LOG.info("Sending messages which do not contain initial size")
+        try_write(b"")
+        try_write(b"\x00")
+        for size in range(1, 4):
+            # NB: Regardless of what these bytes contain!
+            for i in range(5):
+                msg = random.getrandbits(8 * size).to_bytes(size, byteorder="little")
+                try_write(msg)
+
+        LOG.info("Sending messages which do not contain initial header")
+        for size in range(0, 16):
+            try_write(struct.pack("<I", size) + b"\x00" * size)
+
+        LOG.info("Sending plausible messages")
+        try_write(encode_msg())
+        try_write(encode_msg(msg_type=1))
+        try_write(encode_msg(msg_type=100))
+        try_write(encode_msg(sender="abcd"))
+        try_write(encode_msg(body=struct.pack("<QQQQ", 100, 200, 300, 400)))
+        try_write(
+            encode_msg(
+                msg_type=2, sender="abcd", body=struct.pack("<QQQQ", 100, 200, 300, 400)
+            )
+        )
+
+        LOG.info("Sending messages with incorrect sender length")
+        try_write(encode_msg(sender="abcd", sender_len_override=0))
+        try_write(encode_msg(sender="abcd", sender_len_override=1))
+        try_write(encode_msg(sender="abcd", sender_len_override=5))
+        try_write(
+            b"\x0b\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00\x00bbbb"
+        )
+
+        LOG.info("Sending messages with randomised bodies")
+        for _ in range(10):
+            body_len = random.randrange(10, 100)
+            body = random.getrandbits(body_len * 8).to_bytes(body_len, "little")
+            try_write(encode_msg(msg_type=random.randrange(0, 3), body=body))
+
+        # Don't fill the output with failure messages from this probing
+        network.ignore_error_pattern_on_shutdown(
+            "Exception in bool ccf::Channel::recv_key_exchange_message"
+        )
+        network.ignore_error_pattern_on_shutdown("Unknown node message type")
+        network.ignore_error_pattern_on_shutdown("Unhandled AFT message type")
+        network.ignore_error_pattern_on_shutdown("Unknown frontend msg type")
+
+
 if __name__ == "__main__":
     args = infra.e2e_args.cli_args()
     args.package = "samples/apps/logging/liblogging"
 
+    args.nodes = infra.e2e_args.nodes(args, 1)
+    run_node_socket_robustness_tests(args)
+
     # Set a relatively low cap on max open sessions, so we can saturate it in a reasonable amount of time
     args.max_open_sessions = 40
     args.max_open_sessions_hard = args.max_open_sessions + 5
 
     args.nodes = infra.e2e_args.nodes(args, 1)
     args.initial_user_count = 1
-    run(args)
+
+    run_connection_caps_tests(args)