CVE-2026-63388: libevent Reachable Assertion

Vulnerability summary

CVE-2026-63388 is a high (CVSS 8.4) Reachable Assertion vulnerability in libevent. EPSS estimates a 0.14% chance of exploitation in the next 30 days, higher than 3.1% of scored vulnerabilities.

Timeline

1. 20-08-2026
   PublishedVulnerability first disclosed.
2. 21-08-2026
   Last modifiedVulnerability information updated.

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.

• CWE-617Reachable AssertionThe product contains an assert() or similar statement that can be triggered by an attacker, which leads to an application exit or other behavior that is more severe than necessary.
• CWE-787Out-of-bounds WriteThe product writes data past the end, or before the beginning, of the intended buffer.