CVE-2026-63388 Libevent: Heap out-of-bounds write in bufferevent_socket_set_conn_address_ reachable via AF_UNIX accept
A heap out-of-bounds write in Libevent allows local attackers to corrupt memory and potentially execute code via AF_UNIX sockets when assertions are disabled.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-63388?
CVE-2026-63388 is a high-severity memory corruption vulnerability in libevent, published on 20 Aug 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Official description
Libevent is an event notification library. Prior to 2.1.13 and 2.2.2-alpha, libevent has a heap out-of-bounds write in bufferevent_sock.c when bufferevent_socket_set_conn_address_ copies a kernel-supplied AF_UNIX peer address into bufferevent_private.conn_address. Release builds compiled with NDEBUG disable the EVUTIL_ASSERT length guard, and the evhttp accept path can pass a 110-byte sockaddr from accept() into the 28-byte field. An unauthenticated local peer able to connect to an AF_UNIX listener can overwrite the adjacent dns_request pointer and heap data, causing memory corruption with confidentiality, integrity, and availability impact. This issue is fixed in versions 2.1.13 and 2.2.2-alpha.
Which versions are affected by CVE-2026-63388?
How do I fix CVE-2026-63388?
Upgrade to a fixed version.
Upgrade to the fixed version. Memory-safe languages, compiler hardening and fuzzing prevent most new cases. More about Memory corruption.
Is CVE-2026-63388 being exploited?
There is no known exploitation of CVE-2026-63388 in the wild and no public exploit code.
Sources
Also known as AZL-96909, AZL-96956, AZL-97518, AZL-97563, BELL-CVE-2026-63388, DEBIAN-CVE-2026-63388 and 4 more.