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Vulnerability record · CVE-2026-52845 · published 23 June 2026

CVE-2026-52845: Caddyserver caddy improper authentication vulnerability

Caddyserver · Caddy

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.

8.1 CVSS 3.1 High EPSS 0.45% · top 63.8% CWE-287 · Improper authenticationCWE-290 · Authentication bypass by spoofing
8.1CVSS 3.1 base score
0.45%EPSS exploitation probability, 30 days
NoNot in CISA KEV
1Affected product versions listed by NVD
5References, 2 tagged exploit
15 Jul 2026Last modified by NVD

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.

CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:N

Affected products

1 vulnerable configurations from NVD's CPE data, grouped by vendor and product.

References

LinkTags
https://github.com/caddyserver/caddy/security/advisories/GHSA-f59h-q822-g45g ExploitThird Party Advisory
https://access.redhat.com/security/cve/CVE-2026-52845
https://bugzilla.redhat.com/show_bug.cgi?id=2491907
https://github.com/caddyserver/caddy/security/advisories/GHSA-f59h-q822-g45g ExploitThird Party Advisory
https://security.access.redhat.com/data/csaf/v2/vex/2026/cve-2026-52845.json

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Related vulnerabilities

Same products first, then exploited flaws of the same weakness class.

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Source: NIST National Vulnerability Database (record CVE-2026-52845), CISA KEV, FIRST EPSS (scores of 2026-09-26). This page is refreshed as NVD updates the record.