Time-of-check Time-of-use (TOCTOU) Race Condition in undici - CVE-2026-6733
Published: June 17, 2026
Vulnerability identifier: #VU134751
CSH Severity: Low
CVSS v4.0: CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N/E:U/U:Clear
CVE-ID: CVE-2026-6733
CWE-ID: CWE-367
Exploitation vector: Remote access
Exploit availability:
No public exploit available
Vendor: Node.js
Affected software:
undici
undici
Detailed vulnerability description
The vulnerability allows a remote attacker to cause responses to be delivered to the wrong requests.
The vulnerability exists due to a time-of-check time-of-use race condition in the HTTP/1.1 client when reusing keep-alive sockets. A remote attacker can inject an unsolicited HTTP/1.1 response onto an idle socket to cause responses to be delivered to the wrong requests.
Exploitation requires an attacker-controlled or compromised upstream HTTP/1.1 server and keep-alive connection reuse.
How to mitigate CVE-2026-6733
Install security update from vendor's website.