Resource exhaustion in Libevent

CVE-2026-63495

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.

Vulnerability class: DoS (Denial of Service)

Published · last modified .

CVSS v3 metric

CVSS v3 base score 7.5 (High). Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H.

EPSS exploit prediction

EPSS: 0.006 (47.3th percentile), scored .

Very low probability of exploitation in the next 30 days; routine patching cadence is appropriate. 47th percentile — 47.3% of CVEs in the catalogue have a lower EPSS than this one. How to read EPSS.

EPSS trend (30 days)EPSS over the last 30 days for CVE-2026-63495: held from 0.004 to 0.006.

EPSS over last 30 days · oldest: 0.004 · newest: 0.006 · change: +0.002

Affected products

  • Libevent — versions >= 2.2.0-alpha-dev, < 2.2.2-alpha

Weakness classification (CWE)

References

Frequently asked questions

What is CVE-2026-63495?
CVE-2026-63495 is a high-severity vulnerability in Libevent, classified under Uncontrolled Resource Consumption. CVSS score: 7.5/10. Published 2026-08-20.
How severe is CVE-2026-63495?
High severity. CVSS v3 base score is 7.5 out of 10.