Forge: TLS client crash on a handshake record received without a session

Summary

A forge.tls client throws an uncaught TypeError from connection.process() when it receives a ServerHello while it has no session: after a close_notify alert or a call to close(), or before handshake() is called. A malicious server or an on-path attacker can use this to terminate a Node.js process. Fixed in node-forge 1.4.3.

Details

tls.handleHandshake() in lib/tls.js updates the handshake digests with c.session.md5.update(bytes) before it calls the message handler. A client creates its session in handshake(), and c.reset() sets it to null when the connection is closed. Closing doesn't set the fail flag, and the client goes back to expecting a ServerHello, so a Handshake record received afterwards still reaches handleHandshake(), which throws TypeError: Cannot read properties of null (reading 'md5').

This happens:

• after the server sends a close_notify alert (at any alert level);
• after the application calls close();
• before the application calls handshake().

The exception propagates out of connection.process(). Applications that pass socket data to process() from a data event handler without catching exceptions, as in the README example, terminate. After a reset the connection uses no encryption, so an on-path attacker can inject the records even when the real server is honest.

Servers are not affected: a server creates its session when it receives a ClientHello.

The fix handles these records like other unexpected records on a closed client: they are ignored.

Patches

Fixed in node-forge 1.4.3.

Workarounds

Catch exceptions thrown by connection.process() and close the socket, or stop passing socket data to process() once the closed callback has been called and until handshake() is called again.

Resources

• RFC 5246, section 7.2.1 (Closure Alerts): https://www.rfc-editor.org/rfc/rfc5246#section-7.2.1
• Related: GHSA-525v-9gp9-w22h (another TLS client TypeError, fixed in 1.4.1): https://github.com/digitalbazaar/forge/security/advisories/GHSA-525v-9gp9-w22h

Severity

CVSS 3.1: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:N/A:H (5.9, Moderate) CVSS 4.0 (informational): CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N (8.2) CVSS 4.0 has no counterpart to 3.1's AC:H beyond AT:P and scores this higher; the severity rating follows CVSS 3.1.

Credits

Reported by @manus-use.

Proof of concept

var c = forge.tls.createConnection({server: false, ...}); c.handshake(); // warning close_notify alert, then an empty ServerHello, in separate // process() calls c.process(forge.util.hexToBytes('15030100020100')); c.process(forge.util.hexToBytes('160301000402000000')); // <= 1.4.2: TypeError: Cannot read properties of null (reading 'md5') // 1.4.3: the record is ignored

The reporter's PoC is in tests/pocs/ghsa-j8rw-jp99-435v.js, and regression tests are in tests/unit/tls.js.

Impact

Applications that use forge.tls as a client and pass data from a network socket to connection.process() are affected. The server they connect to, or an on-path attacker, can make process() throw; if the application doesn't catch it, the Node.js process terminates, dropping all its connections. Servers built on forge.tls are not affected. There is no confidentiality or integrity impact.