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Vulnerabilities

Vulnerability · CVE-2026-109855

undici is an HTTP client library for Node.js.

Published Oct 15, 2026 · catalog updated Oct 15, 2026 · undici is an HTTP

Check if you run it

No confirmed exploitation is on record for CVE-2026-109855. EPSS is 0.28%. Act only if a listed version of undici is an HTTP is installed.

Gaps on this record

  • The stored product name is a package slug. The name on this page is taken from the title (undici is an HTTP).
  • No vendor fix or required action is stored. Compare the linked advisory before you change production.
Severity
High7.5
Known exploitation
Not in CISA/VulnCheck KEV
EPSS
0.28%
Remediation
Advisory link
Affected products
Debian:14 node-undici · package npm · vendor undici undici

undici is an HTTP client library for Node.js. In versions 8.11.0 and 8.11.1, its experimental WebSocket client, which is enabled by default when HTTP/2 is allowed, mishandles a failed WebSocket handshake over HTTP/2: the request is already marked completed, so the abort becomes a no-op and the underlying HTTP/2 stream is left open with no error listener. When a malicious server then destroys the connection, the orphaned stream emits an unhandled error and the Node.js process exits. A remote, unauthenticated server can therefore crash any client that opens a WebSocket to it over HTTP/2, resulting in a denial of service. The issue is fixed in undici 8.11.2, and users should upgrade to 8.11.2 or later. As a workaround, set allowH2 to false to disable HTTP/2 for WebSocket connections, or avoid opening WebSocket connections to untrusted servers.

Are you affected?

Enter the version you run. The result uses only the ranges stored on this record.

The check returns affected, not affected, or incomplete. It does not guess a version that is missing from the record.

  • Debian:14 node-undici7.15.0+dfsg+~cs3.2.0-1, 7.15.0+dfsg+~cs3.2.0-3, 7.16.0+dfsg+~cs3.2.0-1
  • package npmversion unspecified
  • vendor undici undiciversion unspecified

How to fix CVE-2026-109855

What to do

Three questions, each answered from this record only. Confirm the vendor advisory before you patch.

Should you patch?

No confirmed exploitation is on record for CVE-2026-109855. EPSS is 0.28%. Act only if a listed version of undici is an HTTP is installed.

Which versions are affected?

Compare what you have installed with 7.15.0+dfsg+~cs3.2.0-1, 7.15.0+dfsg+~cs3.2.0-3, 7.16.0+dfsg+~cs3.2.0-1. Compare the installed version with the linked vendor advisory before you change production.

What should an analyst verify?

CWE-248; CWE-754. EPSS 0.28%. There is no CISA KEV listing. No Exploit-DB or Metasploit reference is linked. Use the source links for the original advisory.

Technology hubs

Debian security

Code

The project this record applies to. Exploit listings stay in References.

Timeline

Detection, updates, and resolution for this record.

  1. Oct 15, 2026 · NIST NVD

    Detected

    undici is an HTTP client library for Node.js. In versions 8.11.0 and 8.11.1, its experimental WebSocket client, which is enabled by default when HTTP/2 is allowed, mishandles a failed WebSocket handshake over HTTP/2: the request is already marked completed, so the abort becomes a no-op and the underlying HTTP/2 stream is left open with no error listener. When a malicious server then destroys the c

  2. Oct 15, 2026 · NIST NVD

    Updated

    undici is an HTTP client library for Node.js. In versions 8.11.0 and 8.11.1, its experimental WebSocket client, which is enabled by default when HTTP/2 is allowed, mishandles a failed WebSocket handshake over HTTP/2: the request is already marked completed, so the abort becomes a no-op and the underlying HTTP/2 stream is left open with no error listener. When a malicious server then destroys the c

  3. Oct 15, 2026 · OpenSSF OSV / OSV Scanner

    Updated

    undici is an HTTP client library for Node.js. In versions 8.11.0 and 8.11.1, its experimental WebSocket client, which is enabled by default when HTTP/2 is allowed, mishandles a failed WebSocket handshake over HTTP/2: the request is already marked completed, so the abort becomes a no-op and the underlying HTTP/2 stream is left open with no error listener. When a malicious server then destroys the c

Sources

  • CIRCL Vulnerability LookupVulnerability recordCVE-2026-109855

    undici is an HTTP client library for Node.js. In versions 8.11.0 and 8.11.1, its experimental WebSocket client, which is enabled by default when HTTP/2 is allowed, mishandles a failed WebSocket handshake over HTTP/2: the request is already marked completed, so the abort becomes a

    vulnerability.circl.lu
  • CVE.orgVulnerability recordCVE-2026-109855

    Official CVE identifier

    cve.org
  • FIRST EPSSExploitation probabilityCVE-2026-109855

    30-day exploitation probability 0.3%

    first.org
  • NIST NVDVulnerability recordCVE-2026-109855

    undici is an HTTP client library for Node.js. In versions 8.11.0 and 8.11.1, its experimental WebSocket client, which is enabled by default when HTTP/2 is allowed, mishandles a failed WebSocket handshake over HTTP/2: the request is already marked completed, so the abort becomes a

    nvd.nist.gov
  • OpenSSF OSV / OSV ScannerPackage advisoryDEBIAN-CVE-2026-109855
    osv.dev
  • Snyk Vulnerability DatabasePackage advisorySNYK-JS-UNDICI-20954499

    Uncaught Exception

    security.snyk.io

References

Freshness

Last verified in this catalog Oct 18, 2026. Significant claims (KEV, EPSS, CVSS, affected ranges) come from the source rows above — open the original publisher for the authoritative advisory.