Inconsistent interpretation of HTTP requests in libevent - #VU136942
Published: July 6, 2026
Vulnerability identifier: #VU136942
CSH Severity: Low
CVSS v4: 6.3 [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]
CVE-ID: N/A
CWE-ID: CWE-444
Exploitation vector: Remote access
Exploit availability:
No public exploit available
Vulnerability details
The vulnerability allows a remote attacker to inject headers.
The vulnerability exists due to inconsistent interpretation of HTTP requests in evhttp_header_is_valid_value when handling folded header lines. A remote attacker can send a specially crafted request containing obs-fold sequences to inject headers.
Exploitation depends on a proxy chain where the frontend rejects obs-fold but the libevent backend accepts it.
Affected software
libevent
Remediation
Install security update from vendor's website.
libevent - update to 2.1.13