Summary
Kirby CMS's system API endpoint leaks installed version and license data to authenticated users
TL;DR
This vulnerability affects all Kirby sites that might have potential attackers in the group of authenticated Panel users.
Introduction
Missing authorization allows authenticated users to perform actions they are not intended to have access to.
The effects of missing authorization can include unauthorized access to sensitive information as well as unauthorized changes to content or system information.
Credits
Kirby thanks @HuajiHD and @0x-bala for responsibly reporting the identified issue.
Impact
Kirby's user permissions control which user role is allowed to perform specific actions in the CMS. These permissions are defined for each role in the user blueprint (site/blueprints/users/...). The permissions control the authorization of user actions (with handling of model-specific authorization omitted here for brevity).
Kirby provides the access.system permission (among others) that controls access to the system area of the Kirby Panel. This area contains internal system information like the installed Kirby, plugin and server versions, security state and Kirby license. If the access.system permission is disabled for a user role, users of that role should not be able to access this internal system information. However it is also possible to access some system information via the /api/system REST API endpoint. In affected releases, the response of this endpoint for authenticated users contained the installed Kirby version and the status, type and code of the installed Kirby license. These values are considered sensitive information and should be protected by the access.system permission.
The installed Kirby version and license data can be used by malicious actors during reconnaissance when planning a separate attack.
The application does not perform an authorization check before performing a sensitive operation. Typical impact: unauthorized access to restricted functionality or data.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
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The problem has been patched in Kirby 4.9.0 and Kirby 5.4.0. Please update to one of these or a later version to fix the vulnerability.
In all of the mentioned releases, we have protected the version and license properties of the /api/system endpoint with a check for the existing access.system permission. This ensures that the REST API only outputs information that should be accessible to the user via the Panel.
Frequently Asked Questions
- What is CVE-2026-42051? CVE-2026-42051 is a medium-severity missing authorization vulnerability in getkirby/cms (composer), affecting versions <= 4.8.0. It is fixed in 4.9.0, 5.4.0. The application does not perform an authorization check before performing a sensitive operation.
- Which versions of getkirby/cms are affected by CVE-2026-42051? getkirby/cms (composer) versions <= 4.8.0 is affected.
- Is there a fix for CVE-2026-42051? Yes. CVE-2026-42051 is fixed in 4.9.0, 5.4.0. Upgrade to this version or later.
- Is CVE-2026-42051 exploitable, and should I be worried? Whether CVE-2026-42051 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2026-42051 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2026-42051?
- Upgrade
getkirby/cmsto 4.9.0 or later - Upgrade
getkirby/cmsto 5.4.0 or later
- Upgrade