Node.js is vulnerable to a denial of service attack when a client sends many pipelined HTTP requests on a single connection, and the client does not read the responses from the connection.

We recommend that anyone using Node.js v0.8 or v0.10 to run HTTP servers in production please update as soon as possible.

• v0.10.21 http://blog.nodejs.org/2013/10/18/node-v0-10-21-stable/
• v0.8.26 http://blog.nodejs.org/2013/10/18/node-v0-8-26-maintenance/

This is fixed in Node.js by pausing both the socket and the HTTP parser whenever the downstream writable side of the socket is awaiting a drain event. In the attack scenario, the socket will eventually time out, and be destroyed by the server. If the "attacker" is not malicious, but merely sends a lot of requests and reacts to them slowly, then the throughput on that connection will be reduced to what the client can handle.

There is no change to program semantics, and except in the pathological cases described, no changes to behavior.

If upgrading is not possible, then putting an HTTP proxy in front of the Node.js server can mitigate the vulnerability, but only if the proxy parses HTTP and is not itself vulnerable to a pipeline flood DoS.

For example, nginx will prevent the attack (since it closes connections after 100 pipelined requests by default), but HAProxy in raw TCP mode will not (since it proxies the TCP connection without regard for HTTP semantics).

This addresses CVE-2013-4450.