What’s Vulnerable › Vulnerabilities

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

• Severity: high (CVSS 7.5 v3.1)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.6% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-08-20 · updated 2026-10-26
• Weakness: CWE-400

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 products

• libevent: from 2.2.0-alpha-dev, < 2.2.2-alpha

References

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

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