# CVE-2026-52845: caddy: Caddy is an extensible server platform that uses TLS by default

CVE-2026-52845 is fixed in 2 products on 1 platform, first by DEBIAN-CVE-2026-52845, released June 23, 2026. It is not reported as exploited. Patch Radar priority: High.

- Web page: https://patchblox.com/security/cve/CVE-2026-52845
- Priority: High
- CVSS: 8.1 (high)
- EPSS: 0.0045
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Jun 23, 2026

## 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.

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | caddy Debian 12.15 (bookworm) | 2.6.2-5+deb12u1 | [DEBIAN-CVE-2026-52845](https://patchblox.com/security/data/fix/linux/debian-cve-2026-52845.md) | Jun 23, 2026 |
| Linux | caddy Debian 13.5 (trixie) | 2.6.2-12+deb13u1 | [DEBIAN-CVE-2026-52845](https://patchblox.com/security/data/fix/linux/debian-cve-2026-52845.md) | Jun 23, 2026 |
| Linux | caddy Debian 14 | 2.11.4-1 | [DEBIAN-CVE-2026-52845](https://patchblox.com/security/data/fix/linux/debian-cve-2026-52845.md) | Jun 23, 2026 |
| Linux | govulncheck-vulndb opensuse-leap 16.0 | 0.0.20260727T201416-160000.1.1 | [OPENSUSE-SU-2026:21551-1](https://patchblox.com/security/data/fix/linux/opensuse-su-2026-21551-1.md) | Aug 10, 2026 |
| Linux | govulncheck-vulndb sles 16.0 | 0.0.20260727T201416-160000.1.1 | [SUSE-SU-2026:23227-1](https://patchblox.com/security/data/fix/linux/suse-su-2026-23227-1.md) | Aug 10, 2026 |

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Data as of 2026-11-08T00:53:09Z UTC. Source: Patchblox Patch Radar (https://patchblox.com/security/patch-radar). Patchblox finds out-of-date software on Windows, macOS and Linux and updates it through release rings: https://patchblox.com/demo

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