---
id: CVE-2026-63379
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 processes chunked HTTP trailers in http.c through evhttp_read_trailer
  and merges them into request headers. The fix introduces
  evhttp_parse_headers_impl…
severity: medium
cvss: 6.3
cvssVector: 'CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N'
cwe:
  - CWE-444
vendor: libevent
product: libevent
affected:
  - libevent < 2.1.13
  - 'libevent >= 2.2.0-alpha, < 2.2.2-alpha'
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-2026-63379'
references:
  - url: >-
      https://github.com/libevent/libevent/commit/87e8e44fa774e9677b089b1a5114ee68aefa1636
    label: security-advisories@github.com
  - url: >-
      https://github.com/libevent/libevent/commit/b847071141b3827900d536594ec9045eb0a4c485
    label: security-advisories@github.com
  - 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-2gmv-p5m7-98p6
    label: security-advisories@github.com
  - url: >-
      https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-63379.json
  - url: 'https://access.redhat.com/security/cve/CVE-2026-63379'
  - url: 'https://bugzilla.redhat.com/show_bug.cgi?id=2520667'
  - url: 'https://www.cve.org/CVERecord?id=CVE-2026-63379'
  - url: 'https://nvd.nist.gov/vuln/detail/CVE-2026-63379'
  - url: 'https://access.redhat.com/errata/RHSA-2026:67909'
  - url: 'https://access.redhat.com/errata/RHSA-2026:67910'
  - url: 'https://access.redhat.com/errata/RHSA-2026:60853'
  - url: 'https://access.redhat.com/errata/RHSA-2026:71603'
tags:
  - nvd
  - cve.org
  - csaf
  - vex
  - red-hat
ssvc:
  exploitation: none
  automatable: 'yes'
  technicalImpact: partial
  timestamp: '2026-08-25T15:14:11.010475Z'
cvssSource: cna
ingestedAt: '2026-09-10T16:54:16.894Z'
epss: 0.00707
epssPercentile: 0.51406
patched:
  - enterprise_linux_appstream_v_10
  - enterprise_linux_appstream_v_9
  - enterprise_linux_baseos_v_10
  - enterprise_linux_baseos_v_9
  - hardened_images
scores:
  cna: 6.3
  vendor: 6.5
---

## Overview

Libevent is an event notification library. Prior to 2.1.13 and 2.2.2-alpha, libevent processes chunked HTTP trailers in http.c through evhttp_read_trailer and merges them into request headers. The fix introduces evhttp_parse_headers_impl_ and a temporary trailer header list. An unauthenticated remote attacker can place security-sensitive fields in trailers so that an upstream proxy and the libevent application interpret different effective headers, enabling header smuggling, authorization bypass, proxy-header spoofing, or cache poisoning. The fix parses trailers into a temporary header list and discards them instead of merging them into req->input_headers. 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-2026:67909** · 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-2026:67910** · 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-2026:60853** · Red Hat · fixed in: Red Hat Hardened Images · released 2026-08-29 · [advisory](https://access.redhat.com/errata/RHSA-2026:60853)
- **Red Hat VEX** · Moderate · affected: Red Hat Enterprise Linux 6, Red Hat Enterprise Linux 7, Red Hat Enterprise Linux 8, Red Hat OpenShift Container Platform 4 · no fix planned: Red Hat Enterprise Linux 6, Red Hat Enterprise Linux 7, Red Hat Enterprise Linux 8, Red Hat OpenShift Container Platform 4 · updated 2026-09-24 · [vex](https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-63379.json)
- **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)