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.

The remote Debian 13 host has a package installed that is affected by multiple vulnerabilities as referenced in the dsa-6429 advisory.

    - -------------------------------------------------------------------------     Debian Security Advisory DSA-6429-1                   security@debian.org     https://www.debian.org/security/                                  Aron Xu     August 11, 2026                       https://www.debian.org/security/faq
    - -------------------------------------------------------------------------

    Package        : caddy     CVE ID         : CVE-2026-27585 CVE-2026-27587 CVE-2026-27588 CVE-2026-27589                      CVE-2026-27590 CVE-2026-45692 CVE-2026-52845 CVE-2026-52846

    Multiple security issues were discovered in Caddy, a web server with     automatic HTTPS, which may result in the bypass of path- or host-based     access controls, the execution of an unintended file by a FastCGI     backend, the injection of identity headers trusted by applications     running behind Caddy, unauthorised reconfiguration of the server through     its admin API, or cross-site scripting.

    The fix for CVE-2026-52845 follows upstream in dropping every request     header whose name contains an underscore, for all servers and without an     opt-out. Deployments which pass such headers through Caddy, for instance     X_Api_Key or gRPC custom metadata keys containing underscores, need to     switch to the hyphenated spelling.

    For the stable distribution (trixie), these problems have been fixed in     version 2.6.2-12+deb13u1.

    We recommend that you upgrade your caddy packages.

    For the detailed security status of caddy please refer to     its security tracker page at:
    https://security-tracker.debian.org/tracker/caddy

    Further information about Debian Security Advisories, how to apply     these updates to your system and frequently asked questions can be     found at: https://www.debian.org/security/

    Mailing list: debian-security-announce@lists.debian.org

Tenable has extracted the preceding description block directly from the Debian security advisory.

Note that Nessus has not tested for these issues but has instead relied only on the application's self-reported version number.

The Linux/Unix host has one or more packages installed that are impacted by a vulnerability without a vendor supplied patch available.

  - 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. (CVE-2026-52845)

Note that Nessus relies on the presence of the package as reported by the vendor.

There are packages installed that are affected by a vulnerability referenced in the following CVE:

  - 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. (CVE-2026-52845)

The version of FreeBSD installed on the remote host is prior to tested version. It is, therefore, affected by multiple vulnerabilities as referenced in the 94f93681-6775-11f1-8044-002590af0794 advisory.

    Caddy project reports:
    Caddy 2.11.4 contains multiple security fixes.
    GitHub Security Advisory GHSA-qrp7-cvwr-j2c6 reports:
    Windows-encoded backslashes in request paths could bypass           path-scoped authorization rules before files are served by           file_server.
    GitHub Security Advisory GHSA-f59h-q822-g45g reports:
    forward_auth copy_headers could fail to remove           underscore aliases of copied identity headers before FastCGI header           normalization, allowing identity or group header spoofing.
    GitHub Security Advisory GHSA-vcc4-2c75-vc9v reports:
    The stripHTML template function could fail to remove           malformed HTML, potentially allowing client-side cross-site           scripting if untrusted output is later rendered as HTML.

Tenable has extracted the preceding description block directly from the FreeBSD security advisory.

Note that Nessus has not tested for these issues but has instead relied only on the application's self-reported version number.

ID	Name	Product	Family	Type	Severity
334443	Debian dsa-6429 : caddy - security update	Nessus	Debian Local Security Checks	Local	critical
322431	Linux Distros Unpatched Vulnerability : CVE-2026-52845	Nessus	Misc.	Local	high
443346	SCA: security update for github.com/caddyserver/caddy/v2 (GHSA-f59h-q822-g45g)	Tenable Cloud Security	SCA Checks	Local	high
443346	SCA: security update for github.com/caddyserver/caddy/v2 (GHSA-f59h-q822-g45g)	Tenable Self-Hosted Container Security	SCA Checks	Local	high
321073	FreeBSD : caddy -- multiple vulnerabilities (94f93681-6775-11f1-8044-002590af0794)	Nessus	FreeBSD Local Security Checks	Local	high

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