Stack-based buffer overflow in libevent - CVE-2026-63387

Vulnerability identifier: #VU136940

CSH Severity: Medium

CVSS v4: 8.3 [CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:L/VI:L/VA:H/SC:N/SI:N/SA:N]

CVE-ID: CVE-2026-63387

CWE-ID: CWE-121

Exploitation vector: Remote access

Exploit availability: No public exploit available

The vulnerability allows a remote attacker to cause a denial of service or corrupt adjacent stack state.

The vulnerability exists due to stack-based buffer overflow in dnsname_to_labels() in evdns.c when formatting DNS server responses containing name-bearing records. A remote attacker can send a specially crafted DNS query that causes the application to generate a crafted response to cause a denial of service or corrupt adjacent stack state.

The issue is triggered by an off-by-one condition when name encoding reaches the exact end of a 64 KB stack buffer before a terminating null byte is appended.

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-doc
libevent-devel
libevent
libevent (Red Hat package)
libevent-debuginfo
libevent-debugsource
libevent (Ubuntu package)
libevent (Debian package)

Install security update from vendor's website.

libevent - update to 2.1.13
libevent-doc - addressed in versions 2.1.8-11, 2.1.12-5
libevent-devel - addressed in versions 2.1.8-11, 2.1.12-5
libevent - addressed in versions 2.1.8-11, 2.1.12-5
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 - addressed in versions 2.1.13-1.fc43, 2.1.13-1.fc44, 2.1.13-1.fc45
libevent (Ubuntu package) - addressed in versions 2.0.21-stable-1ubuntu1.14.04.2+esm2, 2.0.21-stable-2ubuntu0.16.04.1+esm2, 2.1.8-stable-4ubuntu0.1~esm2, 2.1.11-stable-1ubuntu0.1~esm2, 2.1.12-stable-1ubuntu0.2, 2.1.12-stable-9ubuntu2.2, 2.1.12-stable-10ubuntu0.2
libevent (Debian package) - update to 2.1.13-stable-1~deb13u1

• https://github.com/libevent/libevent/security/advisories/GHSA-58rx-7448-jw47

• 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
• 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
• Ubuntu update for libevent