CVE-2026-52845
Caddy: FastCGI header normalization bypass in `forward_auth copy_headers`
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.
INFO
Published Date :
June 23, 2026, 5:52 p.m.
Last Modified :
June 23, 2026, 5:52 p.m.
Remotely Exploit :
No
Source :
GitHub_M
Solution
- Update Caddy to version 2.11.4 or later.
- Validate forward_auth and PHP/FastCGI header handling.
- Review Caddy configuration for secure header settings.
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