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A GitHub-reviewed security advisory, not necessarily under active exploitation the way our CISA KEV advisories are, but a real, disclosed vulnerability in an open-source dependency.
Affected packages
Vulnerable: >= 6.7.0, < 6.28.1
Patched in 6.28.1
Vulnerable: >= 7.0.0, < 7.29.1
Patched in 7.29.1
Vulnerable: >= 8.0.0, < 8.10.2
Patched in 8.10.2
Details
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.
Upgrade to undici 6.28.1, 7.29.1, or 8.10.2.
No workaround is available. The fix must be applied through an upgrade.
EPSS, exploit probability
Low0.39%
estimated chance of real-world exploitation in the next 30 days, higher than 34.1% of every CVE FIRST.org scores
Refreshed 11/14/2026, via FIRST.org's EPSS model, not CVSS, this measures likelihood of exploitation, not how severe it would be.
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