GHSA-rfgv-xxqx-mfg5

ghsaUSosv

undici vulnerable to Denial of Service via unrequested WebSocket subprotocol

view advisory published 2026-09-29Licence: CC-BY-4.0

### 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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describes (1)

Related CVEs.

IDseverity exploitable
CVE-2026-19534US——
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 WebSoc…
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references

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