Input validation error in libevent - CVE-2026-63382

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: CVE-2026-63382

CWE-ID: CWE-20

Exploitation vector: Remote access

Exploit availability: No public exploit available

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.

libevent
Debian Linux
IBM i
Anolis OS
Red Hat Enterprise Linux for x86_64
Red Hat Enterprise Linux for IBM z Systems
Red Hat Enterprise Linux for Power, little endian
Red Hat Enterprise Linux for ARM 64
Ubuntu
openEuler
Fedora
libevent (Ubuntu package)
libevent-doc
libevent-devel
libevent
libevent (Red Hat package)
libevent-debugsource
libevent-debuginfo
libevent (Debian package)

Install security update from vendor's website.

libevent - addressed in versions 2.1.13, 7.0
libevent (Ubuntu package) - addressed in versions 2.0.21-stable-2ubuntu0.16.04.1+esm1, 2.0.21-stable-1ubuntu1.14.04.2+esm1, 2.1.8-stable-4ubuntu0.1~esm1, 2.1.11-stable-1ubuntu0.1~esm1, 2.1.12-stable-1ubuntu0.1, 2.1.12-stable-10ubuntu0.1, 2.1.12-stable-9ubuntu2.1
libevent-doc - update to 2.1.8-11
libevent-devel - update to 2.1.8-11
libevent - update to 2.1.8-11
libevent (Red Hat package) - addressed in versions 2.1.8-11.el8_10, 2.1.13-1.el10_2
libevent-devel - update to 2.1.12-17
libevent-debugsource - update to 2.1.12-17
libevent-debuginfo - update to 2.1.12-17
libevent - update to 2.1.12-17
libevent (Debian package) - update to 2.1.13-stable-1~deb13u1
libevent - addressed in versions 2.1.13-1.fc43, 2.1.13-1.fc44, 2.1.13-1.fc45

• https://github.com/libevent/libevent/security/advisories/GHSA-q39v-w2g7-gr8j
• https://www.rfc-editor.org/rfc/rfc9110#section-7.2

• Multiple vulnerabilities in libevent
• openEuler update for libevent
• Ubuntu update for libevent
• Fedora 45 update for libevent
• Fedora 44 update for libevent
• Fedora 43 update for libevent
• Debian update for libevent
• Multiple vulnerabilities in IBM i
• Red Hat Enterprise Linux 8 update for libevent
• Red Hat Enterprise Linux 10 update for libevent
• Anolis OS update for libevent