Input validation error in libevent - #VU136946
Published: July 6, 2026
Vulnerability identifier: #VU136946
CSH Severity: Medium
CVSS v4: 6.3 [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]
CVE-ID: N/A
CWE-ID: CWE-20
Exploitation vector: Remote access
Exploit availability:
No public exploit available
Vulnerability details
The vulnerability allows a remote attacker to smuggle HTTP requests and bypass access controls.
The vulnerability exists due to improper input validation in the evhttp HTTP parser when processing requests with multiple Transfer-Encoding headers. A remote attacker can send a specially crafted request with conflicting Transfer-Encoding headers to smuggle HTTP requests and bypass access controls.
Exploitation requires the service to be deployed behind an intermediary that interprets Transfer-Encoding differently and reuses the connection.
Affected software
libevent
Remediation
Install security update from vendor's website.
libevent - addressed in versions 2.1.13, 7.0