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.
Metrics
CVSS 3.1 8.1/10
CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:NWeakness enumeration
Affected software
| Vendor | Product | Versions |
|---|---|---|
| caddyserver | caddy | < 2.11.4 |
| Red Hat | Red Hat Hardened Images | — |
References
- https://github.com/caddyserver/caddy/security/advisories/GHSA-f59h-q822-g45gExploit, Third Party Advisory
- https://access.redhat.com/security/cve/CVE-2026-52845
- https://bugzilla.redhat.com/show_bug.cgi?id=2491907
- https://github.com/caddyserver/caddy/security/advisories/GHSA-f59h-q822-g45gExploit, Third Party Advisory
- https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-52845.json
Timeline
- Published
- Jun 23, 2026
- Last modified
- Oct 25, 2026
- NVD status
- Modified