undici WebSocket client vulnerable to Denial of Service via failed HTTP/2 handshake
The advisory, in context
Impact
undici's experimental WebSocket client (enabled by default via allowH2: true) crashes the Node.js process when it connects to a malicious server over HTTP/2. If the server answers the WebSocket upgrade with a response that fails handshake validation, undici aborts the request, but the abort is a no-op because the request is already marked completed, so the underlying ClientHttp2Stream is left open with no error listener. When the server then destroys the connection, the orphaned stream emits an unhandled error and the process exits. A remote, unauthenticated server can therefore deny service to any client that opens a WebSocket to it over HTTP/2. undici 8.11.0 and 8.11.1 are affected; the regression was introduced in 8.11.0.
Patches
Upgrade to 8.11.2.
Workarounds
Set allowH2: false to disable HTTP/2 for WebSocket connections, or avoid opening WebSocket connections to untrusted servers, until upgrading.
Affected packages
Start with the recorded fix for your release branch. Check your installed version and test compatibility before upgrading. Fixing this advisory does not rule out other vulnerabilities in the release.
From 8.11.0 before 8.11.2
Fixed in 8.11.2
View affected-version evidence
{
"ranges": [
{
"events": [
{
"introduced": "8.11.0"
},
{
"fixed": "8.11.2"
}
],
"type": "SEMVER"
}
],
"versions": []
}References
- https://github.com/nodejs/undici/security/advisories/GHSA-qq8j-7v2v-3rwp
- https://nvd.nist.gov/vuln/detail/CVE-2026-109855
- https://github.com/nodejs/undici/pull/5873
- https://github.com/nodejs/undici/commit/dd28c5c55f4a25f7c441fd4365b1191f96c3b8bf
- https://cna.openjsf.org/security-advisories.html
- https://github.com/nodejs/undici
- https://github.com/nodejs/undici/releases/tag/v8.11.2