CVE-2026-52845 - Caddy: FastCGI header normalization bypass in `forward_auth copy_headers`

[Starburst-David]

CVE ID: CVE-2026-52845
Published: June 23, 2026
Description: Caddy is an extensible server platform that uses TLS by default. Prior to 2.11.4, forward_auth copy_headers deletes the exact client-supplied identity header before copying the trusted value from the auth gateway. But when the request later goes through php_fastcgi, Caddy normalizes HTTP headers into CGI variables by replacing - with _. This lets a client send an underscore alias that survives the forward_auth delete step but becomes the same PHP/FastCGI variable. Result: a remote client can inject or sometimes override identity/group headers trusted by PHP/FastCGI applications behind Caddy. This vulnerability is fixed in 2.11.4.
Severity: 8.1 | HIGH

More Information:
https://cvefeed.io/vuln/detail/CVE-2026-52845