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CVE-2026-19534GHSA-rfgv-xxqx-mfg5

undici vulnerable to Denial of Service via unrequested WebSocket subprotocol

undici undicinpmLibraries & packages
Open in ThreatlineRecord JSON
CVSS
7.5High
ExploitationNo known exploitationNot in CISA KEV, which does not prove it is unexploitedCISA KEV
Exploit odds (EPSS)0.39%Chance of exploitation activity in the next 30 days, higher than 32% of CVEs. Scored 23 Oct 2026FIRST EPSS
Fixed in6.28.1Also 7.29.1, 8.10.2GitHub
Published4 Sep 2026Updated 29 Sep 2026CVE List

What fixes it

A fixed version on one release line is not the upgrade target for every line. Check your exact version and any vendor backports.

Description

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.

Text from GitHub Advisory Database

Affected versions 12

  • undici, npm>= 6.7.0, < 6.28.1GitHub
  • undici, npm>= 7.0.0, < 7.29.1GitHub
  • undici, npm>= 8.0.0, < 8.10.2GitHub
  • undiciaffected: 6.7.0 before 6.28.1CVE List
  • undiciunaffected: 6.28.1CVE List
  • undiciaffected: 7.0.0 before 7.29.1CVE List
  • undiciunaffected: 7.29.1CVE List
  • undiciaffected: 8.0.0 before 8.10.2CVE List
  • undiciunaffected: 8.10.2CVE List
  • undici, npmfrom 6.7.0, fixed in 6.28.1OSV
  • undici, npmfrom 7.0.0, fixed in 7.29.1OSV
  • undici, npmfrom 8.0.0, fixed in 8.10.2OSV

References 10