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.
Problem types
CWE-287: Improper Authentication
CWE-290: Authentication Bypass by Spoofing
CWE-444: Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling')
Product status
References
github.com/.../caddy/security/advisories/GHSA-f59h-q822-g45g
github.com/.../caddy/security/advisories/GHSA-f59h-q822-g45g