Log in Start free

Vulnerability · Published Aug 20, 2026 · Assigned by GitHub_M

CVE-2026-63387Libevent: Off-by-one stack buffer overflow in dnsname_to_labels via crafted DNS server response

High 7.0

In plain English

A high-severity stack buffer overflow in libevent from libevent. Proof-of-concept exploit code is public. The chance it is exploited in the next 30 days is estimated at 0.4% (higher than 36% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 3.1)7.0High
Exploit odds (30 days)0.4%top 63.9% of all CVEs
Exploited in the wildNo reportsCISA SSVC: poc
Attack toolingNoneno public tooling known

Official description

Libevent is an event notification library. Prior to 2.1.13 and 2.2.2-alpha, libevent has an off-by-one stack buffer overflow in evdns.c when dnsname_to_labels formats a name-bearing DNS record at the end of the 64 KB stack buffer allocated by evdns_server_request_format_response. The final-label check permits j plus label_len plus one to equal buf_len, after which the terminating null byte is written to buf[buf_len]. A crafted DNS server response containing PTR, CNAME, MX, NS, or SOA data can trigger the one-byte out-of-bounds write and crash or corrupt the process. This issue is fixed in versions 2.1.13 and 2.2.2-alpha.

Affected packages & fixed versions

EcosystemPackageFixed inAdvisory
AlmaLinux:10libevent2.1.13-1.el10_2ALSA-2026:67909
AlmaLinux:8libevent2.1.8-11.el8_10ALSA-2026:67908
AlmaLinux:9libevent2.1.13-1.el9_8ALSA-2026:67910
AlmaLinux:10libevent-devel2.1.13-1.el10_2ALSA-2026:67909
AlmaLinux:8libevent-devel2.1.8-11.el8_10ALSA-2026:67908
AlmaLinux:9libevent-devel2.1.13-1.el9_8ALSA-2026:67910
AlmaLinux:10libevent-doc2.1.13-1.el10_2ALSA-2026:67909
AlmaLinux:8libevent-doc2.1.8-11.el8_10ALSA-2026:67908
AlmaLinux:9libevent-doc2.1.13-1.el9_8ALSA-2026:67910
Debian:12libevent2.1.12-stable-8+deb12u1DEBIAN-CVE-2026-63387
Debian:13libevent2.1.13-stable-1~deb13u1DEBIAN-CVE-2026-63387
Debian:14libevent2.1.13-stable-1DEBIAN-CVE-2026-63387
Rocky Linux:10libevent0:2.1.13-1.el10_2RLSA-2026:67909
Rocky Linux:8libevent0:2.1.8-11.el8_10RLSA-2026:67908
Rocky Linux:9libevent0:2.1.13-1.el9_8RLSA-2026:67910
Ubuntu:22.04:LTSlibeventno fix listedUBUNTU-CVE-2026-63387
Ubuntu:22.04:LTSlibevent2.1.12-stable-1ubuntu0.2USN-8840-1
Ubuntu:24.04:LTSlibevent2.1.12-stable-9ubuntu2.2USN-8840-1
Ubuntu:24.04:LTSlibeventno fix listedUBUNTU-CVE-2026-63387
Ubuntu:26.04:LTSlibevent2.1.12-stable-10ubuntu0.2USN-8840-1
Ubuntu:26.04:LTSlibevent2.1.12-stable-10ubuntu0.2UBUNTU-CVE-2026-63387

Affected products (as reported)

VendorProductVersions
libevent libevent >= 2.2.0-alpha, < 2.2.2-alpha< 2.1.13

Weakness: CWE-121, CWE-193, CWE-787 · Vector: CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:H

References