Out-of-bounds write in libevent - CVE-2026-63388

Vulnerability identifier: #VU136938

CSH Severity: Low

CVSS v4: 8.5 [CVSS:4.0/AV:L/AC:L/AT:N/PR:L/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N]

CVE-ID: CVE-2026-63388

CWE-ID: CWE-787

Exploitation vector: Local access

Exploit availability: No public exploit available

The vulnerability allows a remote attacker to execute arbitrary code.

The vulnerability exists due to an out-of-bounds write in bufferevent_socket_set_conn_address_ when processing AF_UNIX accept() results for peer socket addresses. A remote attacker can connect to a vulnerable Unix domain socket with a specially crafted abstract-namespace address to execute arbitrary code.

On builds with NDEBUG, the assertion guarding the copy is disabled. Exploitation requires access to connect to the application's AF_UNIX listener, and on pthread-enabled servers the overwrite can corrupt a lock pointer that is later dereferenced inside libc.

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

Install security update from vendor's website.

libevent - update to 2.1.13
libevent - update to 2.1.8-11
libevent-devel - update to 2.1.8-11
libevent-doc - 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 - update to 2.1.12-17
libevent-debuginfo - update to 2.1.12-17
libevent-debugsource - update to 2.1.12-17
libevent-devel - 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-cvq5-vrvr-j338

• Multiple vulnerabilities in libevent
• openEuler 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