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Libevent: HTTP Header smuggling

libevent · CVE-2026-63379
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What is it?

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.

Evidence

No coverage recorded yet.

Exploitation

  • Public proof of concept
  • Exploited in the wild
  • Listed as known exploited
CVSS
6.3
EPSS
0.7%
First seen
7 d ago
Status
corroborated

All libevent vulnerabilities