CVE-2026-52845
published 2026-06-23CVE-2026-52845: 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…
PriorityP350high8.1CVSS 3.1
AVNACLPRLUINSUCHIHAN
EPSS
0.25%
15.8th percentile
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
3 ranges
| Vendor | Product | Version range | Fixed in |
|---|---|---|---|
| caddyserver | caddy | < 2.11.4 | 2.11.4 |
| github.com | caddyserver_caddy | 0 – 1.0.5 | — |
| github.com | caddyserver_caddy_v2 | >= 0 < 2.11.4 | 2.11.4 |
CVSS provenance
nvdv3.18.1HIGHCVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:N
vendor_redhat8.1HIGH
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Red Hat
github.com/caddyserver/caddy: Caddy: Remote client can inject or override identity headers via header normalization
vendor_redhat·2026-06-23·CVSS 8.1
CVE-2026-52845 [HIGH] CWE-444 github.com/caddyserver/caddy: Caddy: Remote client can inject or override identity headers via header normalization
github.com/caddyserver/caddy: Caddy: Remote client can inject or override identity headers via header normalization
A flaw was found in Caddy, an extensible server platform. A remote attacker can exploit a vulnerability in the `forward_auth` `copy_headers` functionality. This occurs because Caddy normalizes HTTP headers into Common Gateway Interface (CGI) variables by replacing hyphens with underscores, allowing a client to send an underscore alias that bypasses the header deletion step. This enables the remote attacker to inject or override identity and group headers trusted by PHP/FastCGI applications operating behind Caddy.
Package: caddy (Red Hat Hardened Images) - Not affected
GHSA
Caddy: FastCGI header normalization bypass in `forward_auth copy_headers`
ghsa·2026-06-16
CVE-2026-52845 [HIGH] CWE-287 Caddy: FastCGI header normalization bypass in `forward_auth copy_headers`
Caddy: FastCGI header normalization bypass in `forward_auth copy_headers`
### Summary
`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:
```text
Remote-Groups -> HTTP_REMOTE_GROUPS
Remote_Groups -> HTTP_REMOTE_GROUPS
Remote-User -> HTTP_REMOTE_USER
Remote_User -> HTTP_REMOTE_USER
```
Result: a remote client can inject or sometimes override identity/group headers trusted by PHP/FastCGI applications behind Caddy.
### Details
`forward_auth copy_
No detection rules found.
No public exploits indexed.
Bugzilla
CVE-2026-52845 caddy: Caddy: Remote client can inject or override identity headers via header normalization [fedora-all]
bugzilla·2026-06-25·CVSS 8.1
CVE-2026-52845 [HIGH] CVE-2026-52845 caddy: Caddy: Remote client can inject or override identity headers via header normalization [fedora-all]
CVE-2026-52845 caddy: Caddy: Remote client can inject or override identity headers via header normalization [fedora-all]
Disclaimer: Community trackers are created by Red Hat Product Security team on a best effort basis. Package maintainers are required to ascertain if the flaw indeed affects their package, before starting the update process.
Bugzilla
CVE-2026-52845 caddy: Caddy: Remote client can inject or override identity headers via header normalization [epel-all]
bugzilla·2026-06-25·CVSS 8.1
CVE-2026-52845 [HIGH] CVE-2026-52845 caddy: Caddy: Remote client can inject or override identity headers via header normalization [epel-all]
CVE-2026-52845 caddy: Caddy: Remote client can inject or override identity headers via header normalization [epel-all]
Disclaimer: Community trackers are created by Red Hat Product Security team on a best effort basis. Package maintainers are required to ascertain if the flaw indeed affects their package, before starting the update process.
Bugzilla
CVE-2026-52845 github.com/caddyserver/caddy: Caddy: Remote client can inject or override identity headers via header normalization
bugzilla·2026-06-23·CVSS 8.1
CVE-2026-52845 [HIGH] CVE-2026-52845 github.com/caddyserver/caddy: Caddy: Remote client can inject or override identity headers via header normalization
CVE-2026-52845 github.com/caddyserver/caddy: Caddy: Remote client can inject or override identity headers via header normalization
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.
https://github.com/caddyserver/caddy/security/advisories/GHSA-f59h-q822-g45ghttps://access.redhat.com/security/cve/CVE-2026-52845https://bugzilla.redhat.com/show_bug.cgi?id=2491907https://github.com/caddyserver/caddy/security/advisories/GHSA-f59h-q822-g45ghttps://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-52845.json
2026-06-23
Published