---
id: CVE-2026-63495
title: Libevent is an event notification library
summary: >-
  Libevent is an event notification library. From 2.2.0-alpha-dev until
  2.2.2-alpha, the libevent WebSocket server in ws.c accumulates fragmented
  frames in evws->incomplete_frames without enforcing a total message-size
  limit. An unauthenti…
severity: high
cvss: 7.5
cvssVector: 'CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H'
cwe:
  - CWE-400
  - CWE-770
vendor: libevent
product: libevent
affected:
  - 'libevent >= 2.2.0-alpha-dev, < 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-2026-63495'
references:
  - url: >-
      https://github.com/libevent/libevent/commit/291c4d1cd75695e898030ebd5c4ddf26c094077b
    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-qx89-wf2v-vgmx
    label: security-advisories@github.com
  - url: >-
      https://github.com/libevent/libevent/security/advisories/GHSA-qx89-wf2v-vgmx
    label: 134c704f-9b21-4f2e-91b3-4a467353bcc0
  - url: >-
      https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-63495.json
  - url: 'https://access.redhat.com/security/cve/CVE-2026-63495'
  - url: 'https://bugzilla.redhat.com/show_bug.cgi?id=2520659'
  - url: 'https://www.cve.org/CVERecord?id=CVE-2026-63495'
  - url: 'https://nvd.nist.gov/vuln/detail/CVE-2026-63495'
  - url: 'https://access.redhat.com/errata/RHSA-2026:41176'
tags:
  - nvd
  - cve.org
  - exploit-available
  - csaf
  - vex
  - red-hat
exploitAvailable: true
ssvc:
  exploitation: poc
  automatable: 'yes'
  technicalImpact: partial
  timestamp: '2026-08-20T19:16:58.376889Z'
ingestedAt: '2026-09-13T19:13:42.043Z'
epss: 0.00609
epssPercentile: 0.46923
patched:
  - hardened_images
---

## Overview

Libevent is an event notification library. From 2.2.0-alpha-dev until 2.2.2-alpha, the libevent WebSocket server in ws.c accumulates fragmented frames in evws->incomplete_frames without enforcing a total message-size limit. An unauthenticated remote client can repeatedly send fragmented WebSocket frames below WS_MAX_RECV_FRAME_SZ with FIN=0, causing the evbuffer to grow without bound until the process or host exhausts memory. This issue is fixed in version 2.2.2-alpha.

## Remediation

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

## Vendor advisories

- **RHSA-2026:41176** · Red Hat · fixed in: Red Hat Hardened Images · released 2026-07-17 · [advisory](https://access.redhat.com/errata/RHSA-2026:41176)
- **Red Hat VEX** · Important · affected: Red Hat Enterprise Linux 6, Red Hat OpenShift Container Platform 4 · no fix planned: Red Hat Enterprise Linux 6, Red Hat OpenShift Container Platform 4 · updated 2026-09-16 · [vex](https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-63495.json)