---
id: CVE-2026-63387
title: Libevent is an event notification library
summary: >-
  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 allocat…
severity: high
cvss: 7
cvssVector: 'CVSS:3.1/AV:N/AC:H/PR:N/UI:N/S:U/C:L/I:L/A:H'
cwe:
  - CWE-121
  - CWE-193
  - CWE-787
vendor: libevent
product: libevent
affected:
  - 'libevent >= 2.2.0-alpha, < 2.2.2-alpha'
  - libevent < 2.1.13
published: '2026-08-20'
updated: '2026-09-09'
sourceUpdated: '2026-09-09T21:19:49.197'
source: NVD
sourceUrl: 'https://nvd.nist.gov/vuln/detail/CVE-2026-63387'
references:
  - url: 'https://github.com/libevent/libevent/releases/tag/release-2.1.13-stable'
    label: security-advisories@github.com
  - url: 'https://github.com/libevent/libevent/releases/tag/release-2.2.2-alpha'
    label: security-advisories@github.com
  - url: >-
      https://github.com/libevent/libevent/security/advisories/GHSA-58rx-7448-jw47
    label: security-advisories@github.com
  - url: >-
      https://github.com/libevent/libevent/security/advisories/GHSA-58rx-7448-jw47
    label: 134c704f-9b21-4f2e-91b3-4a467353bcc0
  - url: >-
      https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-63387.json
  - url: 'https://access.redhat.com/security/cve/CVE-2026-63387'
  - url: 'https://bugzilla.redhat.com/show_bug.cgi?id=2520655'
  - url: 'https://www.cve.org/CVERecord?id=CVE-2026-63387'
  - url: 'https://nvd.nist.gov/vuln/detail/CVE-2026-63387'
  - url: 'https://access.redhat.com/errata/RHSA-2026:63388'
  - url: 'https://access.redhat.com/errata/RHSA-2026:67909'
  - url: 'https://access.redhat.com/errata/RHSA-2026:67908'
  - url: 'https://access.redhat.com/errata/RHSA-2026:67910'
  - url: 'https://access.redhat.com/errata/RHSA-2026:71603'
tags:
  - nvd
  - cve.org
  - exploit-available
  - csaf
  - vex
  - red-hat
exploitAvailable: true
ssvc:
  exploitation: poc
  automatable: 'no'
  technicalImpact: partial
  timestamp: '2026-08-25T15:11:49.042805Z'
ingestedAt: '2026-09-13T09:20:54.706Z'
epss: 0.00448
epssPercentile: 0.36422
patched:
  - hardened_images
scores:
  nvd: 7
  vendor: 8.6
---

## Overview

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.

## Remediation

Refer to the linked advisories for vendor-supplied fixes and affected version ranges.

## Vendor advisories

- **RHSA-2026:63388** · Red Hat · fixed in: Red Hat Hardened Images · released 2026-09-03 · [advisory](https://access.redhat.com/errata/RHSA-2026:63388)
- **Red Hat VEX** · Important · affected: Red Hat Enterprise Linux 6, Red Hat Enterprise Linux 7, Red Hat OpenShift Container Platform 4 · no fix planned: Red Hat Enterprise Linux 6, Red Hat Enterprise Linux 7, Red Hat OpenShift Container Platform 4 · updated 2026-09-24 · [vex](https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-63387.json)
- **RHSA-2026:67909** · Red Hat · fixed in: Red Hat Enterprise Linux AppStream (v. 10), Red Hat Enterprise Linux BaseOS (v. 10) · released 2026-09-16 · [advisory](https://access.redhat.com/errata/RHSA-2026:67909)
- **RHSA-2026:67908** · Red Hat · fixed in: Red Hat Enterprise Linux AppStream (v. 8), Red Hat Enterprise Linux BaseOS (v. 8) · released 2026-09-16 · [advisory](https://access.redhat.com/errata/RHSA-2026:67908)
- **RHSA-2026:67910** · Red Hat · fixed in: Red Hat Enterprise Linux AppStream (v. 9), Red Hat Enterprise Linux BaseOS (v. 9) · released 2026-09-16 · [advisory](https://access.redhat.com/errata/RHSA-2026:67910)
- **RHSA-2026:71603** · Red Hat · fixed in: Red Hat Update Infrastructure 5 · released 2026-09-24 · [advisory](https://access.redhat.com/errata/RHSA-2026:71603)