RHSA-2026:73428

undici's WebSocket client crashes the whole Node.js process during the opening handshake when a server responds with a subprotocol that the client never requested. A default WebSocket connection sends no subprotocol, but if the server's 101 response includes a Sec-WebSocket-Protocol header, undici dereferences a null value while checking it against the requested list and throws an uncaught TypeError. Because that code runs inside a microtask with no surrounding error handling, the exception propagates and terminates the process under Node's default behavior, instead of gracefully failing the connection as required by the WebSocket protocol. Any application that opens a WebSocket to an attacker-controlled or compromised server, or over a plaintext connection subject to a machine-in-the-middle, can be crashed remotely without authentication in the default configuration. This affects undici versions from 6.7.0 up to 6.28.1, from 7.0.0 up to 7.29.1, and from 8.0.0 up to 8.10.2. Users should upgrade to undici 6.28.1, 7.29.1, or 8.10.2.

undici's BalancedPool constructor passes its entire options object through an internal deep-clone that serializes and reparses the value as JSON. Because JSON cannot represent functions, any function-valued TLS option, such as a caller-supplied checkServerIdentity callback or a custom connector inside the connect option, is silently discarded before it reaches the TLS layer. As a result a peer whose certificate the application's custom checkServerIdentity was written to reject, but which still passes Node's default hostname and chain checks, is accepted when reached through BalancedPool. The Client, Pool, and Agent dispatchers are not affected because they extract the connect and tls options before cloning. This affects undici versions from 7.24.1 up to 7.29.1 and from 8.0.0 up to 8.10.2, and only when the application supplies a function-valued connect or tls option to BalancedPool. Users should upgrade to undici 7.29.1 or 8.10.2.

undici 8.10.0 omits the destination origin from the cache and request-deduplication keys when the cache or deduplicate interceptor is composed directly onto a Client or Pool. Because the internal cache key falls back to an empty origin string, a cacheable or in-flight response from one upstream origin is returned for a request to a different, trusted origin whenever the method, path, and relevant headers match, which permits cross-origin information disclosure and persistent cache poisoning. The reporter demonstrated a full authentication bypass in which a JWT signed with an attacker-controlled key was accepted as belonging to a trusted issuer, and the trusted origin was never contacted. This is a regression introduced in 8.10.0 and affects undici versions from 8.10.0 up to 8.10.2. Applications using an Agent, which carries the origin in its dispatch options, are not affected. Users should upgrade to undici 8.10.2.