Kirby CMS Missing Authorization Vulnerability

hello@craftedsignal.io — Thu, 30 Apr 2026 21:03:20 +0000

Kirby CMS versions prior to 4.9.0 and between 5.0.0 and 5.3.3 are vulnerable to a missing authorization flaw. This vulnerability impacts Kirby sites where user roles are intentionally configured with restricted access to pages or files through disabled pages.access, pages.list, files.access, or files.list permissions. The issue stems from inconsistent permission checks within the Kirby Panel and REST API, allowing authenticated users to access resources they should not be able to. Updating to versions 4.9.0, 5.4.0, or later resolves this vulnerability by implementing consistent permission checks. The vulnerability is identified as CVE-2026-42137.

Attack Chain

An authenticated user logs into the Kirby CMS Panel or REST API.
The user attempts to access a page or file for which their role lacks the necessary pages.access/files.access or pages.list/files.list permissions.
Due to inconsistent permission checks, the user can view the page or file details via the “changes” dialog in the Panel, even if listing is disabled.
The user accesses the REST API, which, despite direct access checks, fails to properly filter collections or related models (children, drafts, files, etc.).
The attacker views images associated with restricted site, pages, or user resources in lists within the Panel.
The user exploits the incorrect permission check (using pages.access instead of pages.list or files.access instead of files.list in specific API routes).
The user traverses to previous or next files using direct links in the files view, even if those files should not be listable.
The attacker gains unauthorized access to sensitive information or modifies content due to the bypassed permission checks.

Impact

This vulnerability allows authenticated users to bypass intended access restrictions within Kirby CMS, leading to potential unauthorized access to sensitive information and/or unauthorized content modification. The inconsistent permission checks in the Panel and REST API could result in unintended disclosure of data restricted by role-based access controls. Successful exploitation could compromise the confidentiality and integrity of the affected Kirby CMS instance. While the advisory does not list the number of victims, this flaw impacts any Kirby site with restricted roles.

Recommendation

Upgrade to Kirby CMS version 4.9.0 or 5.4.0 (or later) to patch the vulnerability as recommended in the advisory.
Review user role permissions and blueprint configurations to ensure appropriate access controls are in place after patching, as described in the overview.
Monitor web server logs for unusual API requests to resources that should be restricted, using the rules below, to identify potential exploitation attempts.
Implement rate limiting on API endpoints to mitigate potential brute-force attacks attempting to exploit this or other vulnerabilities.

Kirby CMS Missing Authorization Vulnerability

hello@craftedsignal.io — Wed, 03 Jan 2024 12:00:00 +0000

Kirby CMS, a file-based content management system, has a missing authorization flaw that allows authenticated users to access sensitive site, user, and role information without the necessary permissions. This vulnerability affects installations where there are potentially untrusted authenticated users. The issue stems from the lack of permission settings controlling access to the site model, users, and user roles. Specifically, the permissions site.access, user.access, users.access, user.list, and users.list were missing. This vulnerability was reported by @HuajiHD and patched in Kirby versions 4.9.0 and 5.4.0. Sites that explicitly intend all authenticated users to have read access to all site, user, and role information are not affected.

Attack Chain

An attacker obtains valid credentials for a user account with access to the Kirby Panel.
The attacker authenticates to the Kirby Panel using their credentials.
The attacker crafts a request to access the site model data. This could involve accessing specific API endpoints related to site configuration.
The attacker sends a request to list all users within the Kirby CMS.
The system, lacking proper authorization checks, returns the requested site model and user list data to the attacker.
The attacker sends a request to list existing roles, their names, descriptions, and configured permissions.
The system returns the requested role information, again bypassing intended permission restrictions.
The attacker gains unauthorized knowledge of the site structure, user accounts, and role permissions, which can be used to escalate privileges or further compromise the system.

Impact

Successful exploitation of this vulnerability allows an attacker with low-privilege Panel access to enumerate users, roles, and site configurations. This information can be used to identify privileged accounts, understand the site’s structure, and potentially escalate privileges by exploiting other vulnerabilities or misconfigurations. This impacts all Kirby sites using versions <= 4.8.0 and versions >= 5.0.0 and <= 5.3.3 where authenticated users are not fully trusted.

Recommendation

Upgrade to Kirby version 4.9.0 or 5.4.0 or later to patch the vulnerability as described in the advisory.
Review user roles and permissions after upgrading to ensure appropriate access controls are in place.
Monitor web server logs for suspicious requests targeting user and role enumeration endpoints after deploying the below rules.

Cms (>= 5.0.0, <= 5.3.3) — CraftedSignal Threat Feed

Kirby CMS Missing Authorization Vulnerability

Attack Chain

Impact

Recommendation

Kirby CMS Missing Authorization Vulnerability

Attack Chain

Impact

Recommendation