undici vulnerable to Denial of Service via unrequested WebSocket subprotocol — GHSA-RFGV-XXQX-MFG5

Summary

### 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…

Timeline

Published by source

2026-09-29

Risk context

• Reported severity or threat level: high.
• Reported CVSS score: 7.5 out of 10.
• Reported EPSS value: 0.00394.
• Review exposure for the affected product or family: npm: undici.

Product

npm: undici

What to do

General, cautious steps (verify details in the official source):

• Prioritize patching or mitigation immediately (treat as actively risky).
• Identify affected product versions in your inventory and verify whether you are impacted.
• Apply vendor patches/updates or recommended mitigations as soon as available.
• Read the official advisory for exact affected versions and remediation steps.

Official advisory

• Read the official source
• CVE Record
• NVD

Evidence and provenance

Canonical advisory ID

GHSA-RFGV-XXQX-MFG5

Source

GitHub

Vendor

GitHub

Published by source

2026-09-29

Last source activity

2026-09-29

Additional identifiers

CVE-2026-19534

Curated by

hlukh.ch

Related advisories and connections

These advisories are connected by shared CVE, product, vendor, source, or time signals.