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 (CVSS)
| Base score | 8.1 |
|---|---|
| Severity | High |
| Version | CVSS 3.1 |
| Vector | CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:N |
| Provided by | CNA |
Weaknesses
- CWE-287 — CWE-287: Improper Authentication
- CWE-290 — CWE-290: Authentication Bypass by Spoofing
- CWE-444 — CWE-444: Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling')
Affected products
| Vendor | Product | Versions |
|---|---|---|
| caddyserver | caddy | < 2.11.4 |
References
- https://github.com/caddyserver/caddy/security/advisories/GHSA-f59h-q822-g45g (x_refsource_CONFIRM)
Generated from the official CVE List on 24 Jun 2026 09:35 UTC.