Moleculer: Unauthenticated Denial of Service via negative length field in the TCP transporter packet parser

Moleculer is a progressive microservices framework for Node.js. Prior to 0.14.36 and 0.15.2, Parser._write in src/transporters/tcp/parser.js used Buffer.prototype.readInt32BE to read a signed packet length, so a remote unauthenticated peer could supply a negative value that caused packet.slice(length) to return the unchanged buffer while the while (packet.length > 0) loop continued indefinitely. The synchronous loop blocked the Node.js event loop and made every service in the process unresponsive until restart. The TCP transporter must be enabled and reachable, and neither CRC validation nor maxPacketSize prevents the malformed length value. This issue is fixed in versions 0.14.36 and 0.15.2.

Moleculer is a progressive microservices framework for Node.js. Prior to 0.14.36 and 0.15.2, Parser._write in src/transporters/tcp/parser.js used Buffer.prototype.readInt32BE to read a signed packet length, so a remote unauthenticated peer could supply a negative value that caused packet.slice(length) to return the unchanged buffer while the while (packet.length > 0) loop continued indefinitely. The synchronous loop blocked the Node.js event loop and made every service in the process unresponsive until restart. The TCP transporter must be enabled and reachable, and neither CRC validation nor maxPacketSize prevents the malformed length value. This issue is fixed in versions 0.14.36 and 0.15.2.

Moleculer is a progressive microservices framework for Node.js. Prior to 0.14.36 and 0.15.2, Parser._write in src/transporters/tcp/parser.js used Buffer.prototype.readInt32BE to read a signed packet length, so a remote unauthenticated peer could supply a negative value that caused packet.slice(length) to return the unchanged buffer while the while (packet.length > 0) loop continued indefinitely. The synchronous loop blocked the Node.js event loop and made every service in the process unresponsive until restart. The TCP transporter must be enabled and reachable, and neither CRC validation nor maxPacketSize prevents the malformed length value. This issue is fixed in versions 0.14.36 and 0.15.2.

### Summary The TCP transporter's packet parser (`src/transporters/tcp/parser.js`) reads the packet length field with `Buffer.prototype.readInt32BE`, a signed read. A crafted packet whose length field has the sign bit set yields a negative `length`. The parser then advances past the parsed message with `packet = packet.slice(length)`, but `Buffer.prototype.slice` clamps an out-of-range negative start index to `0`, so the buffer is returned unchanged. The `while (packet.length > 0)` loop condition therefore never becomes false, producing an infinite synchronous loop that blocks the Node.js event loop indefinitely. ### Impact Any Moleculer node using the TCP transporter can be rendered completely unresponsive by an unauthenticated remote peer sending a single ~10-byte crafted TCP packet, before any protocol handshake or authentication takes place. `TcpReader.onTcpClientConnected` pipes each accepted socket's bytes straight into a fresh `Parser` instance (`socket.pipe(parser)`) with no handshake, so the code path is reachable by any peer able to reach the transporter's listening port. Because Node.js is single-threaded, the hang blocks the entire event loop of the process, taking down every service hosted in it until it is forcibly restarted. TCP transporter endpoints are frequently auto-discovered via UDP broadcast, so any host on the same network segment can reach the port. Neither the CRC check nor `maxPacketSize` mitigate the issue: the CRC bytes are fully attacker-computable, and `maxPacketSize` bounds the received buffer size, not the value of the length field. ### Affected component `Parser._write` in `src/transporters/tcp/parser.js`. ### Patch The fix validates that the decoded length is at least the 6-byte header size before processing, rejecting negative and undersized values (which would otherwise fail to shrink the buffer) with an error on the write callback instead of looping. ### Credit Reported by xor4xor via the Tidelift security program.