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Vulnerability record · CVE-2026-63495 · published 20 August 2026

CVE-2026-63495: Uncontrolled resource consumption vulnerability

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.

7.5 CVSS 3.1 High EPSS 0.61% · top 53.0% CWE-400 · Uncontrolled resource consumptionCWE-770 · Allocation without limits Awaiting Analysis
7.5CVSS 3.1 base score
0.61%EPSS exploitation probability, 30 days
NoNot in CISA KEV
0Affected product versions listed by NVD
4References
9 Sep 2026Last modified by NVD

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.

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H

References

LinkTags
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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Source: NIST National Vulnerability Database (record CVE-2026-63495), CISA KEV, FIRST EPSS (scores of 2026-09-26). This page is refreshed as NVD updates the record.