# CVE-2026-63379

## Summary

- **CVE ID:** CVE-2026-63379
- **Severity:** MEDIUM
- **CVSS Score:** 6.3 (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)
- **CWE:** CWE-444
- **Published:** Aug 20, 2026
- **Last Modified:** Aug 25, 2026

## 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 Products

- libevent — libevent (< 2.1.13)
- libevent — libevent (>= 2.2.0-alpha, < 2.2.2-alpha)

## References

- [CNA](https://github.com/libevent/libevent/security/advisories/GHSA-2gmv-p5m7-98p6)
- [CNA](https://github.com/libevent/libevent/commit/87e8e44fa774e9677b089b1a5114ee68aefa1636)
- [CNA](https://github.com/libevent/libevent/commit/b847071141b3827900d536594ec9045eb0a4c485)
- [CNA](https://github.com/libevent/libevent/releases/tag/release-2.1.13-stable)
- [CNA](https://github.com/libevent/libevent/releases/tag/release-2.2.2-alpha)

## Exploitation Prediction (EPSS)

- **EPSS Score:** 0.52%
- **EPSS Percentile:** 42.2

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_Exported from OnDuty AI Vulnerability Intelligence on 2026-09-09._