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Vulnerability record · CVE-2026-63385 · published 20 August 2026

CVE-2026-63385: HTTP request smuggling vulnerability

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.

9.2 CVSS 4.0 Critical EPSS 0.55% · top 56.3% CWE-444 · HTTP request smuggling Awaiting Analysis
9.2CVSS 4.0 base score
0.55%EPSS exploitation probability, 30 days
NoNot in CISA KEV
0Affected product versions listed by NVD
5References
9 Sep 2026Last modified by NVD

Description

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.

CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:H/VI:H/VA:L/SC:L/SI:L/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:

References

LinkTags
https://github.com/libevent/libevent/commit/758be0c0f69c1934ef9a84ab39e9f9e5fde2e6d0
https://github.com/libevent/libevent/commit/9170dd35e64714613e8d13b290587cfc28e258e2
https://github.com/libevent/libevent/releases/tag/release-2.1.13-stable
https://github.com/libevent/libevent/releases/tag/release-2.2.2-alpha
https://github.com/libevent/libevent/security/advisories/GHSA-jcwh-pvf2-73p2

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Source: NIST National Vulnerability Database (record CVE-2026-63385), CISA KEV, FIRST EPSS (scores of 2026-09-26). This page is refreshed as NVD updates the record.