Gazelle versions through 0.49 for Perl allows HTTP Request Smuggling via Improper Header Precedence. Gazelle incorrectly prioritizes "Content-Length" over "Transfer-Encoding: chunked" when both headers are present in an HTTP request. Per RFC 7230 3.3.3, Transfer-Encoding must take precedence. An attacker could exploit this to smuggle malicious HTTP requests via a front-end reverse proxy.

• https://datatracker.ietf.org/doc/html/rfc7230#section-3.3.3
• https://security.metacpan.org/patches/G/Gazelle/0.49/CVE-2026-40562-r1.patch
• https://metacpan.org/release/KAZEBURO/Gazelle-0.50/changes