CVE-2026-75592: Kirby: Access to image files outside of the site root via path traversal in the media handling
Kirby is an open-source content management system. Prior to 4.9.5 and 5.5.2, depending on the release line, Kirby's media handler used incomplete filesystem containment checks in src/Filesystem/Dir.php and src/Filesystem/F.php through Kirby\Filesystem\Dir::realpath() and Kirby\Filesystem\F::realpath(). The checks accepted a sibling directory whose path shared the intended root's string prefix, such as /var/www/site2 next to /var/www/site, because they did not require an exact match or a DIRECTORYSEPARATOR boundary. A remote attacker could use Kirby\Cms\Media::thumb() to create and access thumbnails from image files in a PHP-readable sibling directory when that directory contained a valid .json thumbnail job file, potentially exposing staging sites, backups, or other internal sites and deleting the job file during processing. This issue is fixed in versions 4.9.5 and 5.5.2.
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade
Kirbyto a version that resolves this vulnerability.Fixed in 4.9.5 - Upgrade
Upgrade
Kirbyto a version that resolves this vulnerability.Fixed in 5.5.2 - Compensating control
Ensure the web server cannot read or execute files from directories outside the Kirby site root (e.g., via filesystem permissions and/or web server document root restrictions) to limit exposure from image path traversal in Kirby media handling.
Event History
Frequently Asked Questions
Which deployments are realistically exposed to this issue?
Deployments running Kirby versions earlier than 4.9.5 or 5.5.2 are affected, depending on their release line. Exploitation also requires a PHP-readable sibling directory whose filesystem path shares the site root's prefix, such as a site directory next to another directory named with the same prefix.
What does an attacker need to exploit the flaw?
A remote attacker needs to invoke Kirby's media thumbnail handling against an image in a PHP-readable sibling directory. That directory must contain a valid .json thumbnail job file for the media handler to process.
What could be exposed or changed during exploitation?
An attacker can create and access thumbnails derived from image files outside the intended site root, which could expose images from staging sites, backups, or other internal sites. Processing may also delete the thumbnail job file in the sibling directory.
What should be done if an upgrade cannot happen immediately?
The provided information identifies the required exposure conditions but does not specify an official workaround. Prioritize preventing PHP access to sibling directories containing sensitive images and thumbnail job files until upgrading to 4.9.5 or 5.5.2, as appropriate for the release line.