Vulnerability · Published Aug 20, 2026 · Assigned by GitHub_M

CVE-2026-63495Libevent: Unbounded memory accumulation in WebSocket server via fragmented frames

High 7.5

In plain English

A high-severity uncontrolled resource consumption in libevent from libevent. Proof-of-concept exploit code is public. The chance it is exploited in the next 30 days is estimated at 0.6% (higher than 49% of all known vulnerabilities).

Severity (CVSS 3.1)7.5High

Exploit odds (30 days)0.6%top 50.6% of all CVEs

Exploited in the wildNo reportsCISA SSVC: poc

Attack toolingNoneno public tooling known

Official description

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.

Affected packages & fixed versions

Ecosystem	Package	Fixed in	Advisory
Ubuntu:22.04:LTS	libevent	no fix listed	UBUNTU-CVE-2026-63495
Ubuntu:24.04:LTS	libevent	no fix listed	UBUNTU-CVE-2026-63495
Ubuntu:26.04:LTS	libevent	no fix listed	UBUNTU-CVE-2026-63495

Affected products (as reported)

Vendor	Product	Versions
libevent	libevent	>= 2.2.0-alpha-dev, < 2.2.2-alpha

Weakness: CWE-400, CWE-770 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

References

https://github.com/libevent/libevent/security/advisories/GHSA-qx89-wf2v-vgmx x_refsource_CONFIRM
https://github.com/libevent/libevent/commit/291c4d1cd75695e898030ebd5c4ddf26c094077b x_refsource_MISC
https://github.com/libevent/libevent/releases/tag/release-2.2.2-alpha x_refsource_MISC