Vulnerability · Published Aug 20, 2026 · Assigned by GitHub_M
CVE-2026-63379Libevent: HTTP Header smuggling
Medium 6.3
In plain English
A medium-severity security flaw in libevent from libevent. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.7% (higher than 54% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.
Official description
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 packages & fixed versions
| Ecosystem | Package | Fixed in | Advisory |
|---|---|---|---|
| AlmaLinux:10 | libevent | 2.1.13-1.el10_2 | ALSA-2026:67909 |
| AlmaLinux:9 | libevent | 2.1.13-1.el9_8 | ALSA-2026:67910 |
| AlmaLinux:10 | libevent-devel | 2.1.13-1.el10_2 | ALSA-2026:67909 |
| AlmaLinux:9 | libevent-devel | 2.1.13-1.el9_8 | ALSA-2026:67910 |
| AlmaLinux:10 | libevent-doc | 2.1.13-1.el10_2 | ALSA-2026:67909 |
| AlmaLinux:9 | libevent-doc | 2.1.13-1.el9_8 | ALSA-2026:67910 |
| Debian:12 | libevent | 2.1.12-stable-8+deb12u1 | DEBIAN-CVE-2026-63379 |
| Debian:13 | libevent | 2.1.13-stable-1~deb13u1 | DEBIAN-CVE-2026-63379 |
| Debian:14 | libevent | 2.1.13-stable-1 | DEBIAN-CVE-2026-63379 |
| Rocky Linux:10 | libevent | 0:2.1.13-1.el10_2 | RLSA-2026:67909 |
| Rocky Linux:9 | libevent | 0:2.1.13-1.el9_8 | RLSA-2026:67910 |
| Ubuntu:22.04:LTS | libevent | no fix listed | UBUNTU-CVE-2026-63379 |
| Ubuntu:24.04:LTS | libevent | no fix listed | UBUNTU-CVE-2026-63379 |
| Ubuntu:26.04:LTS | libevent | no fix listed | UBUNTU-CVE-2026-63379 |
| Ubuntu:26.10 | libevent | no fix listed | UBUNTU-CVE-2026-63379 |
Affected products (as reported)
Weakness: CWE-444 · Vector: CVSS:4.0/AV:N/AC:L/AT:P/PR:N/UI:N/VC:L/VI:L/VA:N/SC:N/SI:N/SA:N
References
- https://github.com/libevent/libevent/security/advisories/GHSA-2gmv-p5m7-98p6 x_refsource_CONFIRM
- https://github.com/libevent/libevent/commit/87e8e44fa774e9677b089b1a5114ee68aefa1636 x_refsource_MISC
- https://github.com/libevent/libevent/commit/b847071141b3827900d536594ec9045eb0a4c485 x_refsource_MISC
- https://github.com/libevent/libevent/releases/tag/release-2.1.13-stable x_refsource_MISC
- https://github.com/libevent/libevent/releases/tag/release-2.2.2-alpha x_refsource_MISC