CVE-2026-52845

Summary

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.

Affected Software

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')

ADP Enrichment

CISA ADP Vulnrichment

• SSVC:
• Exploitation: poc
  • Automatable: no
  • Technical Impact: total

Additional References

• https://github.com/caddyserver/caddy/security/advisories/GHSA-f59h-q822-g45g

github.com/caddyserver/caddy: Caddy: Remote client can inject or override identity headers via header normalization

Additional References

• https://access.redhat.com/security/cve/CVE-2026-52845
• https://bugzilla.redhat.com/show_bug.cgi?id=2491907
• https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-52845.json

References

• https://github.com/caddyserver/caddy/security/advisories/GHSA-f59h-q822-g45g

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