Out-of-bounds read in libevent - CVE-2026-63383

Vulnerability identifier: #VU136944

CSH Severity: Medium

CVSS v4: 6.9 [CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:L/SC:N/SI:N/SA:N]

CVE-ID: CVE-2026-63383

CWE-ID: CWE-125

Exploitation vector: Remote access

Exploit availability: No public exploit available

The vulnerability allows a remote attacker to cause a denial of service.

The vulnerability exists due to an out-of-bounds read in decode_tag_internal() when parsing a malformed fragmented evbuffer tag. A remote attacker can send specially crafted input with more than 5 continuation bytes to cause a denial of service.

The issue is reachable through evtag_unmarshal_header(), and potential higher-level reachability exists via evrpc request parsing.

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
Ubuntu
openEuler
Fedora
libevent (Ubuntu package)
libevent-doc
libevent-devel
libevent
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 (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 - addressed in versions 2.1.8-11, 2.1.12-7
libevent-devel - addressed in versions 2.1.8-11, 2.1.12-7
libevent - addressed in versions 2.1.8-11, 2.1.12-7
libevent (Red Hat package) - addressed in versions 2.1.8-11.el8_10, 2.1.13-1.el10_2
libevent-debuginfo - update to 2.1.12-17
libevent-devel - update to 2.1.12-17
libevent-debugsource - 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-fj29-64w6-73h6

• 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
• Anolis OS update for libevent
• Red Hat Enterprise Linux 8 update for libevent
• Red Hat Enterprise Linux 10 update for libevent
• Anolis OS update for libevent