CVE-2026-63379
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.
CSIRTS triage
- What
- HTTP header smuggling vulnerability in Libevent HTTP handling.
- Who is affected
- Applications using Libevent for HTTP parsing and request routing.
- Urgency
- Moderate; header smuggling can bypass security controls but specific attack vectors are not detailed.
- Action
- Update Libevent to a patched version once available.
AI-assisted analysis generated from the source advisory — verify against the original.
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Exploitation outlook
- Low exploitation risk0.52% 30-day exploitation probability — currently an unlikely target, but scores change as exploit code circulates. Riskier than 42% of all EPSS-scored CVEs.
Advisory coverage (2)
- unknownCVE-2026-63379: Libevent is an event notification library. Prior to 2.1.13 and 2.2.2-alpha, libevent processes…nvd · 2026-08-20
- unknownCVE-2026-63379: Libevent: HTTP Header smugglingmsrc · 2026-08-11
External references
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