CVE-2026-52845
Caddy: FastCGI header normalization bypass in `forward_auth copy_headers`
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.
How to fix CVE-2026-52845
To remediate CVE-2026-52845, upgrade the affected package to a fixed version below.
- —no fix listed
- —upgrade to 2.11.4 or later
Is CVE-2026-52845 being exploited?
Low — EPSS is 0.2%, meaning exploitation activity has not been observed at scale.
Affected packages (2)
- from 0, <= 1.0.5
- from 0, < 2.11.4
CVSS scores
| Source | Version | Severity | Vector |
|---|---|---|---|
| osv | CVSS 3.1 | HIGH8.1 | CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:N |