Summary
Kirby: Access to image files and limited access to JSON files outside of the site root via path traversal in the media handling
TL;DR
This vulnerability affects all Kirby sites that are deployed to a server that allows requests for URLs with encoded slashes (%2f), such as nginx, PHP's built-in server or Apache setups that have the option AllowEncodedSlashes enabled.
It was possible to create and access thumbnails from media files in arbitrary accessible directories on the server that have a valid thumbnail configuration (JSON job file). It was also possible to detect the presence of files with the .json file extension anywhere on the server.
This vulnerability is of high severity for affected sites.
Server setups using Apache's default configuration or other servers that have been hardened against encoded slashes in URLs are not affected.
Introduction
A path traversal (also known as directory traversal) vulnerability occurs when untrusted input is used to build a filesystem path without properly confining the result to an intended base directory. By injecting sequences such as ../, an attacker can escape that directory and reach files elsewhere on the server.
Affected components
Kirby's media handler processes requests for files in the media directory that have not been generated yet. It parses the provided path and finds the correct file or asset from which to generate a thumbnail. Each thumbnail needs to have a prepared job file (a metadata file with file extension .json) in order to allow the media handler to generate it.
Each parent (such as a page) has its own media directory, which in turn contains the individual files. Kirby's media handler searches for the file within the parent's media directory.
Credits
Thanks to Jorge González Milla (@Pig-Tail) for responsibly reporting the identified issue.
Impact
In affected releases, Kirby did not prevent path traversal in the filenames that were searched within the parent directory. In affected server setups where the attacker can provide encoded slashes (%2f) in the request, Kirby allowed the request to traverse away from the parent's media directory.
Because the response differs between existing and non-existing thumbnail configurations, attackers were able to tell whether an arbitrary JSON file exists on the server (addressed by a relative path from the media directory of an arbitrary existing parent, including a relative path that points outside of the site's index root). For existing files with the file extension .json and a valid filename key (resulting in a valid job file), it was possible to generate thumbnails of the referenced media files, deleting the job file in the process.
Input manipulates file paths to reach files outside the intended directory, such as configuration or credential files. Typical impact: unauthorized file read or write outside the intended directory.
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 4.9.5 and Kirby 5.5.2. Please update to one of these or a later version to fix the vulnerability.
In all of the mentioned releases, Kirby\Cms\Media::thumb() now rejects any filename that contains path information (anything other than a plain filename) before it is appended to the validated root. We have also hardened the file::version component to block paths that contain the ../ sequence.
Frequently Asked Questions
- What is CVE-2026-75594? CVE-2026-75594 is a high-severity path traversal vulnerability in getkirby/cms (composer), affecting versions <= 4.9.4. It is fixed in 4.9.5, 5.5.2. Input manipulates file paths to reach files outside the intended directory, such as configuration or credential files.
- Which versions of getkirby/cms are affected by CVE-2026-75594? getkirby/cms (composer) versions <= 4.9.4 is affected.
- Is there a fix for CVE-2026-75594? Yes. CVE-2026-75594 is fixed in 4.9.5, 5.5.2. Upgrade to this version or later.
- Is CVE-2026-75594 exploitable, and should I be worried? Whether CVE-2026-75594 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-2026-75594 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-2026-75594?
- Upgrade
getkirby/cmsto 4.9.5 or later - Upgrade
getkirby/cmsto 5.5.2 or later
- Upgrade