CVE-2026-63495 Libevent: Unbounded memory accumulation in WebSocket server via fragmented frames
An unauthenticated remote attacker can cause memory exhaustion and denial of service in Libevent WebSocket servers by sending fragmented frames.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-63495?
CVE-2026-63495 is a high-severity denial of service vulnerability in libevent, published on 20 Aug 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
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.
Which versions are affected by CVE-2026-63495?
Linux distribution packages (3)
libevent Red Hat:hummingbird:1 | All versions | 0:2.1.12-19.hum1 |
libevent-devel Red Hat:hummingbird:1 | All versions | 0:2.1.12-19.hum1 |
libevent-doc Red Hat:hummingbird:1 | All versions | 0:2.1.12-19.hum1 |
How do I fix CVE-2026-63495?
Upgrade to a fixed version.
Upgrade, then put limits on request size, rate and nesting depth so one client cannot exhaust the service. More about Denial of service.
Is CVE-2026-63495 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-63495 exists.
Sources
Also known as GHSA-qx89-wf2v-vgmx, RHSA-2026:41176.