CVE-2026-6733

Description

Impact: Undici's HTTP/1.1 client is vulnerable to response queue poisoning on reused keep-alive sockets. An attacker-controlled upstream server can inject an unsolicited HTTP/1.1 response onto an idle socket after a request completes. When the client dispatches the next request on that socket, it associates the injected response with the new request, causing responses to be delivered to the wrong requests. This requires an attacker-controlled or compromised upstream HTTP/1.1 server and keep-alive connection reuse. Patches: Upgrade to undici v6.26.0, v7.28.0 or v8.5.0. Workarounds: Disable keep-alive connection reuse by setting keepAliveTimeout: 0 on the Client or Pool.

CVSS Metrics

• v3.1•LOW•Score: 3.7CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N

EPSS Trends

Current EPSS score: 0.23%• Percentile: 14%

Techniques & Countermeasures

• CWE-367•Time-of-check Time-of-use (TOCTOU) Race Condition

  The product checks the state of a resource before using that resource, but the resource's state can change between the check and the use in a way that invalidates the results of the check.

Affected Systems

• Npm•undici

  < 6.27.0 | ≥ 7.0.0, < 7.28.0 | ≥ 8.0.0, < 8.5.0

• undici•undici

  < 6.26.0 | ≥ 7.0.0, < 7.28.0 | ≥ 8.0.0, < 8.5.0

References (5)

• https://github.com/nodejs/undici/security/advisories/GHSA-35p6-xmwp-9g52
• https://hackerone.com/reports/3582376
• https://cna.openjsf.org/security-advisories.html
• https://nvd.nist.gov/vuln/detail/CVE-2026-6733
• https://github.com/nodejs/undici