Impact
undici's WebSocket client (including Node.js's bundled globalThis.WebSocket) crashes the entire Node.js process when a remote WebSocket peer sends a permessage-deflate compressed message that crosses the decompressed-payload size limit and then contains a malformed DEFLATE block. In lib/web/websocket/permessage-deflate.js, the size-limit cleanup calls removeAllListeners() on the internal zlib InflateRaw, removing its error listener, but leaves the stream running. The inflater then emits a Z_DATA_ERROR with no listener attached, which Node.js treats as a fatal unhandled error event and terminates the process. Application error/close handlers on the public WebSocket cannot observe or prevent this, because the failing object is the internal InflateRaw.
A malicious or compromised WebSocket server can crash a client with a single connection, unauthenticated and without any application mistake. The attack is asymmetric (about 130 KB on the wire expands past the limit) and can be repeated on reconnect (crash loop).
Affected applications are those using the undici WebSocket client (new WebSocket(...)) or Node.js's bundled globalThis.WebSocket that can be induced to connect to an attacker-controlled or compromised WebSocket endpoint.
Patches
Upgrade to undici v6.28.1, v7.29.1 or v8.10.2.
Workarounds
No workaround is available.
References
mcollina Remediation developer
krsecu Reporter
UlisesGascon Remediation reviewer
Impact
undici's WebSocket client (including Node.js's bundled
globalThis.WebSocket) crashes the entire Node.js process when a remote WebSocket peer sends a permessage-deflate compressed message that crosses the decompressed-payload size limit and then contains a malformed DEFLATE block. Inlib/web/websocket/permessage-deflate.js, the size-limit cleanup callsremoveAllListeners()on the internal zlibInflateRaw, removing itserrorlistener, but leaves the stream running. The inflater then emits aZ_DATA_ERRORwith no listener attached, which Node.js treats as a fatal unhandlederrorevent and terminates the process. Applicationerror/closehandlers on the public WebSocket cannot observe or prevent this, because the failing object is the internalInflateRaw.A malicious or compromised WebSocket server can crash a client with a single connection, unauthenticated and without any application mistake. The attack is asymmetric (about 130 KB on the wire expands past the limit) and can be repeated on reconnect (crash loop).
Affected applications are those using the undici WebSocket client (
new WebSocket(...)) or Node.js's bundledglobalThis.WebSocketthat can be induced to connect to an attacker-controlled or compromised WebSocket endpoint.Patches
Upgrade to undici v6.28.1, v7.29.1 or v8.10.2.
Workarounds
No workaround is available.
References