High [CVE-2026-63385] HTTP header handling bugs create risk of access control bypass.

Libevent is an event notification library.

Prior to 2.1.13 and 2.2.2-alpha, libevent has two HTTP parsing weaknesses in http.c. evhttp_decode_uri_internal decodes percent-encoded %00 bytes into literal NUL characters, which can cause downstream C string operations to truncate a path and bypass validation performed on a different representation. evhttp_header_is_valid_value also accepts obsolete line folding in header values containing carriage return or line feed characters, allowing a proxy and libevent to interpret headers differently and enabling header injection or access control bypass.

The CRLF header acceptance is fixed in versions 2.1.13 and 2.2.2-alpha, but the reviewed patches do not clearly remediate the URI NUL-truncation condition. A flaw was found in libevent.

The evhttp_decode_uri_internal function in http.c decodes percent-encoded %00 bytes into literal NUL characters without rejecting them, allowing an attacker to craft a URI such as /admin/secret%00.jpg where extension-based access checks see.jpg but the server processes /admin/secret, bypassing path-based access controls.

Additionally, evhttp_header_is_valid_value accepts obsolete HTTP header line folding (CRLF followed by SP/HT), which RFC 9112 states new implementations should reject, creating a header injection vector in proxy chains where the frontend rejects obs-fold but libevent accepts it.