Caddy: FastCGI header normalization bypass in `forward_auth copy_headers`
Published Jun 23, 2026
8.1
HIGHCVSS 3.1
EPSS 0.45%
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.
Affected products
-
Affected
- < 2.11.4
Default status is the baseline for the product. Each version can override it (patched versions can be marked unaffected).
| Vendor | Product | Default status | Versions |
|---|---|---|---|
| Caddyserver | Caddy | unknown | Affected
|
- < 2.11.4
No data.
Red Hat Hardened Images
caddy
Not affected
| Product | Package | State | Advisory |
|---|---|---|---|
| Red Hat Hardened Images | caddy | Not affected | n/a |
github.com/caddyserver/caddy/v2
Go
Introduced 0 Fixed 2.11.4github.com/caddyserver/caddy
Go
Introduced 0 Fixed not fixed
| Ecosystem | Package | Introduced | Fixed |
|---|---|---|---|
| Go | github.com/caddyserver/caddy/v2 | 0 | 2.11.4 |
| Go | github.com/caddyserver/caddy | 0 | not fixed |
Remediation
No remediation recorded yet.
References (8)
- https://access.redhat.com/security/cve/CVE-2026-52845 Vendor Advisory
- https://bugzilla.redhat.com/show_bug.cgi?id=2491907 Issue Tracking
- https://euvd.enisa.europa.eu/vulnerability/EUVD-2026-38558 Advisory
- https://github.com/advisories/GHSA-f59h-q822-g45g Advisory
- https://github.com/caddyserver/caddy/security/advisories/GHSA-f59h-q822-g45g exploitx_refsource_CONFIRMThird Party Advisory
- https://nvd.nist.gov/vuln/detail/CVE-2026-52845
- https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-52845.json
- https://www.cve.org/CVERecord?id=CVE-2026-52845
| Link | Providers | Tags |
|---|---|---|
| https://access.redhat.com/security/cve/CVE-2026-52845 | Vendor Advisory | |
| https://bugzilla.redhat.com/show_bug.cgi?id=2491907 | Issue Tracking | |
| https://euvd.enisa.europa.eu/vulnerability/EUVD-2026-38558 | Advisory | |
| https://github.com/advisories/GHSA-f59h-q822-g45g | Advisory | |
| https://github.com/caddyserver/caddy/security/advisories/GHSA-f59h-q822-g45g | exploitx_refsource_CONFIRMThird Party Advisory | |
| https://nvd.nist.gov/vuln/detail/CVE-2026-52845 | ||
| https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-52845.json | ||
| https://www.cve.org/CVERecord?id=CVE-2026-52845 |
Change history (0)
No recorded changes yet.
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