CVE-2026-52845
Caddy: FastCGI header normalization bypass in `forward_auth copy_headers`
- Published
- Updated
- Reserved
- Assigned by
- GitHub_M
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.
Scores
| Scored by | CVSS | Score | Vector |
|---|---|---|---|
| GitHub_MCNA (assigner) | 3.1 | High8.1 | CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:N |
| redhat-SADPADP (enrichment) | 3.1 | High8.1 | CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:N |
| NVDNVD · Modified | 3.1 | High8.1 | CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:N |
- EPSS (exploitation in 30 days)
- 0.45% · top 61% of all CVEs (5 Nov 2026)
- CISA SSVC
- Exploitation: poc · Automatable: no · Technical impact: total
The list uses the assigner's score when there is one, then CISA's, then NVD's: High 8.1.
Weakness
- CWE-287: Improper Authentication (opens in a new tab)All about CWE-287 and its CVEs
- CWE-290: Authentication Bypass by Spoofing (opens in a new tab)All about CWE-290 and its CVEs
- CWE-444: Inconsistent Interpretation of HTTP Requests ('HTTP Request/Response Smuggling') (opens in a new tab)All about CWE-444 and its CVEs
Affected products
- affected < 2.11.4
Affected packages
From reviewed advisories of the GitHub Advisory Database.
- Gogithub.com/caddyserver/caddyGHSA-f59h-q822-g45g (opens in a new tab)
- Gogithub.com/caddyserver/caddy/v2GHSA-f59h-q822-g45g (opens in a new tab)
References (4)
- https://github.com/caddyserver/caddy/security/advisories/GHSA-f59h-q822-g45g (opens in a new tab)x_refsource_CONFIRMexploit
- https://access.redhat.com/security/cve/CVE-2026-52845 (opens in a new tab)vdb-entryx_refsource_REDHAT
- RHBZ#2491907 (opens in a new tab)issue-trackingx_refsource_REDHAT
- https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-52845.json (opens in a new tab)x_sadp-csaf-vex
Sources
The same CVE in the primary databases and aggregators, to check against.
- CVE.org record (opens in a new tab)
- CVE List JSON (GitHub) (opens in a new tab)
- NVD (opens in a new tab)
- FIRST EPSS (opens in a new tab)
- OSV.dev (opens in a new tab)
- GitHub Advisory GHSA-f59h-q822-g45g (opens in a new tab)
- CIRCL Vulnerability-Lookup (opens in a new tab)
Badge for a README or a ticket
[](https://trackcve.app/cve/CVE-2026-52845)Record last updated .