Libevent up to 2.1.12 HTTP Parser http.c crlf injection

Summaryinfo

A vulnerability, which was classified as critical, was found in Libevent up to 2.1.12. Affected by this vulnerability is the function evhttp_decode_uri_internal/evhttp_header_is_valid_value of the file http.c of the component HTTP Parser. The manipulation results in crlf injection. This vulnerability is reported as CVE-2026-63385. The attack can be launched remotely. No exploit exists.

Detailsinfo

A vulnerability classified as critical has been found in Libevent up to 2.1.12. Affected is the function evhttp_decode_uri_internal/evhttp_header_is_valid_value of the file http.c of the component HTTP Parser. The manipulation with an unknown input leads to a crlf injection vulnerability. CWE is classifying the issue as CWE-93. The product uses CRLF (carriage return line feeds) as a special element, e.g. to separate lines or records, but it does not neutralize or incorrectly neutralizes CRLF sequences from inputs. This is going to have an impact on confidentiality, integrity, and availability. CVE summarizes:

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.

The advisory is available at github.com. This vulnerability is traded as CVE-2026-63385 since 07/16/2026. The exploitability is told to be easy. It is possible to launch the attack remotely. The exploitation doesn't require any form of authentication. Technical details are known, but there is no available exploit.

Upgrading to version 2.1.13 or 2.2.2-alpha eliminates this vulnerability.

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Productinfo

Name

• Libevent

Version

• 2.1.0
• 2.1.1
• 2.1.2
• 2.1.3
• 2.1.4
• 2.1.5
• 2.1.6
• 2.1.7
• 2.1.8
• 2.1.9
• 2.1.10
• 2.1.11
• 2.1.12

Website

• Product: https://github.com/libevent/libevent/

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