Uncaught Exception Affecting undici package, versions >=8.11.0 <8.11.2
Threat Intelligence
The probability is the direct output of the EPSS model, and conveys an overall sense of the threat of exploitation in the wild. The percentile measures the EPSS probability relative to all known EPSS scores. Note: This data is updated daily, relying on the latest available EPSS model version. Check out the EPSS documentation for more details.
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Test your applications- Snyk IDSNYK-JS-UNDICI-20954499
- published15 Oct 2026
- disclosed15 Oct 2026
- creditJongsik Kim
Introduced: 15 Oct 2026
NewCVE-2026-109855 (opens in a new tab)How to fix?
Upgrade undici to version 8.11.2 or higher.
Overview
undici is an An HTTP/1.1 client, written from scratch for Node.js
Affected versions of this package are vulnerable to Uncaught Exception in the experimental WebSocket client, where a response failing handshake validation triggers an abort that is a no-op because the request is already marked completed, so the underlying ClientHttp2Stream stays open with no error listener attached. An attacker running the server can crash the connecting Node.js process by answering a WebSocket upgrade with a response that fails that validation and then destroying the connection, at which point the orphaned stream emits an unhandled error. This requires the client to open a WebSocket to the attacker's server over HTTP/2, which allowH2: true permits by default.
Workaround
This vulnerability can be avoided by setting allowH2: false, which disables HTTP/2 for WebSocket connections.