Vulnerability in Node.js Undici
CVE-2026-6733
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.
Vulnerability class: TOCTOU (Time-of-Check to Time-of-Use)
Published · last modified .
CVSS v3 metric
CVSS v3 base score 3.7 (Low). Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:N/I:L/A:N.
EPSS exploit prediction
EPSS: 0.003 (17.3th percentile), scored .
Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 17th percentile — 17.3% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.
EPSS over last 30 days · oldest: 0.002 · newest: 0.003 · change: +0.001
Affected products
- Node.js Undici
- Undici — versions 0, 6.26.0, 7.0.0
Weakness classification (CWE)
References
- ce714d77-add3-4f53-aff5-83d477b104bb (Mitigation, Vendor Advisory)
- ce714d77-add3-4f53-aff5-83d477b104bb (Issue Tracking)
- ce714d77-add3-4f53-aff5-83d477b104bb (Vendor Advisory)
Frequently asked questions
- What is CVE-2026-6733?
- CVE-2026-6733 is a low-severity vulnerability in Node.js Undici, classified under Time-of-check Time-of-use (TOCTOU) Race Condition. CVSS score: 3.7/10. Published 2026-06-17.
- How severe is CVE-2026-6733?
- Low severity. CVSS v3 base score is 3.7 out of 10.