CVE-2026-63495
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.
Does this matter?
High impact if exploited, but EPSS currently rates exploitation as unlikely (0.52%). Schedule it in the normal patch cycle and watch for a rise in EPSS or a public exploit.
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
- 7.5 HIGHCVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:N/A:H
- EPSS
- 0.52% probability · 42th percentile
- CISA KEV
- Not listed
- Weakness
- CWE-400, CWE-770
- Source
- security-advisories@github.com
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
Source: NVD record, EPSS from FIRST.org, KEV from CISA. Refreshed daily.