CVE-2026-63385: libevent NUL-Truncation & CRLF Header Injection (2.1.12/2.2.1)
CVE-2026-63385 Published on August 20, 2026
Libevent: 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.
Vulnerability Analysis
CVE-2026-63385 can be exploited with network access, and does not require authorization privileges or user interaction. This vulnerability is considered to have a low attack complexity. The potential impact of an exploit of this vulnerability is considered to have no impact on confidentiality and integrity and availability.
Weakness Type
What is a HTTP Request Smuggling Vulnerability?
When malformed or abnormal HTTP requests are interpreted by one or more entities in the data flow between the user and the web server, such as a proxy or firewall, they can be interpreted inconsistently, allowing the attacker to "smuggle" a request to one device without the other device being aware of it.
CVE-2026-63385 has been classified to as a HTTP Request Smuggling vulnerability or weakness.
Products Associated with CVE-2026-63385
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Affected Versions
libevent:- Version >= 2.2.0-alpha, < 2.2.2-alpha is affected.
- Version < 2.1.13 is affected.