CVE-2026-85014: undici vulnerable to Denial of Service via WebSocketStream unclean close
Impact
undici's WebSocketStream crashes the client process when a WebSocket connection is closed abruptly without a close handshake. On such an unclean close, the internal socket-close handler calls abort() on the writable stream even when the application holds a writer lock. Per the WHATWG Streams standard, aborting a locked stream returns a promise that rejects with a TypeError, and the handler discards that promise. The unobserved rejection surfaces as an unhandledRejection and, under Node.js's default behavior, terminates the process.
A malicious or compromised WebSocket server can crash a client with a single connection teardown (a TCP reset, a proxy teardown, or a protocol-violating frame). Affected applications are those using the WebSocketStream API and writing through a writer, which is the standard way to write.
All releases from undici 7.0.0 are affected. WebSocketStream was introduced in 7.0.0.
Patches
Upgrade to undici v7.29.1 or v8.10.2.
Workarounds
No workaround is available.
Other sources
undici's experimental WebSocketStream client crashes the whole Node.js process when a remote peer closes the TCP connection without a WebSocket close handshake. On an unclean close the internal socket-close handler calls abort on the writable stream unconditionally and discards the returned promise, but per the WHATWG Streams standard aborting a locked writable returns a promise that rejects with a TypeError. Because the application holds a writer on that writable, which is the only way to write, the rejection is never observed and Node's default unhandled-rejection behavior terminates the process. An untrusted server can therefore crash a client with a single abrupt disconnect, with no authentication and no application mistake. This affects undici versions from 7.0.0 up to 7.29.1 and from 8.0.0 up to 8.10.2. Users should upgrade to undici 7.29.1 or 8.10.2.
— MITRE
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade
npm/undicito a version that resolves this vulnerability.Fixed in 8.10.2 - Upgrade
Upgrade
npm/undicito a version that resolves this vulnerability.Fixed in 7.29.1 - Upgrade
Upgrade
undicito a version that resolves this vulnerability.Fixed in 7.29.1 - Upgrade
Upgrade
undicito a version that resolves this vulnerability.Fixed in 8.10.2
Event History
Frequently Asked Questions
Which applications are exposed to this denial of service?
Applications using undici's experimental WebSocketStream client are exposed when they connect to an untrusted or attacker-controlled server. The affected ranges are stated as undici 7.0.0 through 7.29.1 and 8.0.0 through 8.10.2.
What does an attacker need to do to trigger the crash?
The attacker only needs to operate or control a remote peer that can abruptly close the TCP connection without completing a WebSocket close handshake. No authentication or application mistake is required.
How can I determine whether my application is affected?
Check whether the application uses the experimental WebSocketStream client and inventory its installed undici version. The crash condition applies when the application holds a writer on the writable stream, which is required in order to write.
What remediation does the advisory recommend?
The advisory recommends upgrading undici to version 7.29.1 or 8.10.2.