HighGHSA-rfgv-xxqx-mfg5CVE-2026-19534

undici vulnerable to Denial of Service via unrequested WebSocket subprotocol

Published 29 Sept 2026 · Updated 29 Sept 2026

Affected packages

undicinpm

Affected: >=6.7.0 <6.28.1
Fixed in: 6.28.1

Update to the fixed version for your release line, for example:npm install undici@6.28.1

undicinpm

Affected: >=7.0.0 <7.29.1
Fixed in: 7.29.1

Update to the fixed version for your release line, for example:npm install undici@7.29.1

undicinpm

Affected: >=8.0.0 <8.10.2
Fixed in: 8.10.2

Update to the fixed version for your release line, for example:npm install undici@8.10.2

Details

Impact

The undici WebSocket client throws an uncaught TypeError during the opening handshake when a server's 101 response includes a Sec-WebSocket-Protocol header that the client never requested. The throw occurs in a queueMicrotask callback with no surrounding try/catch, so it propagates as an uncaught exception and terminates the Node.js process. This is a remote, unauthenticated denial of service against any application that opens a WebSocket to an attacker controlled or compromised server, or over a plaintext ws:// connection subject to a machine-in-the-middle. It affects the default new WebSocket(url) usage, where no subprotocol is requested. Per RFC 6455 section 4.1, an unrequested subprotocol must fail the connection, not crash it.

All releases starting at undici 6.7.0 are affected.

Patches

Upgrade to undici 6.28.1, 7.29.1, or 8.10.2.

Workarounds

No workaround is available. The fix must be applied through an upgrade.

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References

Advisory data from OSV.dev (opens OSV.dev in a new tab), refreshed daily.