Inconsistent interpretation of HTTP requests in undici - CVE-2026-1525
Published: April 24, 2026
Vulnerability identifier: #VU127581
CSH Severity: Medium
CVSS v4.0: CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N/E:U/U:Green
CVE-ID: CVE-2026-1525
CWE-ID: CWE-444
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 smuggle HTTP requests.
The vulnerability exists due to inconsistent interpretation of HTTP requests in undici low-level HTTP request APIs when processing headers passed as flat arrays with case-variant duplicate Content-Length names. A remote attacker can supply specially crafted header arrays to smuggle HTTP requests.
Exploitation requires an intermediary and backend to interpret duplicate Content-Length headers inconsistently.
How to mitigate CVE-2026-1525
Install security update from vendor's website.