CVE-2026-63379: Libevent

Medium severity, CVSS 6.3. EPSS: 0.7% chance of exploitation in the next 30 days.

Libevent is an event notification library. Prior to 2.1.13 and 2.2.2-alpha, libevent processes chunked HTTP trailers in http.c through evhttp_read_trailer and merges them into request headers. The fix introduces evhttp_parse_headers_impl_ and a temporary trailer header list. An unauthenticated remote attacker can place security-sensitive fields in trailers so that an upstream proxy and the libevent application interpret different effective headers, enabling header smuggling, authorization bypass, proxy-header spoofing, or cache poisoning. The fix parses trailers into a temporary header list and discards them instead of merging them into req->input_headers. This issue is fixed in versions 2.1.13 and 2.2.2-alpha.

Affected products

• Libevent Libevent: before 2.1.13 (fixed in 2.1.13); from 2.2.0-alpha, before 2.2.2-alpha (fixed in 2.2.2-alpha)

Published 2026-08-20. Last modified 2026-09-09.