CVE-2026-44177

Kirby is an open-source content management system. In versions 5.3.0 and above but prior to 5.4.1, Kirby did not correctly validate the provided user ID, resulting in a path traversal vulnerability. Version 5.3.0 introduced a performance improvement to the Users collection that loaded user objects lazily when first needed. Users were queried by their ID, which was then used to locate the corresponding account directory under site/accounts. This affected the authentication API (accessible to unauthenticated requests), the users API (accessible only to authenticated users), and any other place that uses $users->find() to look up an individual user by a request-provided email or ID. As a result, an attacker could trigger arbitrary PHP file inclusion of files named  index.php (for example, the main PHP files of plugins), the impact of which depends on the logic those files contain. It also allowed probing for the existence of arbitrary directories on the server, letting attackers fingerprint the server and site setup, including installed plugins and the content structure. This issue has been fixed in version 5.4.1.

Kirby is an open-source content management system. In versions 5.3.0 and above but prior to 5.4.1, Kirby did not correctly validate the provided user ID, resulting in a path traversal vulnerability. Version 5.3.0 introduced a performance improvement to the Users collection that loaded user objects lazily when first needed. Users were queried by their ID, which was then used to locate the corresponding account directory under site/accounts. This affected the authentication API (accessible to unauthenticated requests), the users API (accessible only to authenticated users), and any other place that uses $users->find() to look up an individual user by a request-provided email or ID. As a result, an attacker could trigger arbitrary PHP file inclusion of files named  index.php (for example, the main PHP files of plugins), the impact of which depends on the logic those files contain. It also allowed probing for the existence of arbitrary directories on the server, letting attackers fingerprint the server and site setup, including installed plugins and the content structure. This issue has been fixed in version 5.4.1.

### TL;DR This vulnerability affects all Kirby sites on Kirby 5.3.0-5.4.0 and is independent from setup conditions and authentication. **This vulnerability is of high severity for all Kirby sites**. ---- ### Introduction Path traversal is a type of attack that allows to access arbitrary filesystem paths. By using special elements such as `..` and `/` separators, attackers can escape outside of the restricted location to access files or directories that are elsewhere on the system. One of the most common special elements is the `../` sequence, which in most modern operating systems is interpreted as the parent directory of the current location. Path traversal can give attackers information about the filesystem and directory structure on the server and can lead to additional attacks depending on the nature of the accessible files and directories. PHP file inclusion is a type of attack that allows to load and execute PHP files on the server that are not intended for direct inclusion. Depending on the logic inside the PHP files, this can lead to disclosure of sensitive information or unintended, malicious actions. ### Affected components Kirby's `Users` collection received a performance improvement in Kirby 5.3.0. Starting in this release, Kirby loads user objects lazily when they are first needed. Users are queried by their user ID, which is then used to look up the user's account directory in the `site/accounts` directory. This applies to the authentication API (accessible to unauthenticated requests), the users API (accessible to authenticated users only) as well as to other places that use `$users->find()` to look up an individual user with a request-provided email or user ID. ### Impact In affected releases, Kirby did not correctly validate the provided user ID, causing a path traversal vulnerability. This vulnerability results in the following impact: - Arbitrary PHP file inclusion of files with the filename `index.php` (e.g. the main PHP files of plugins), the impact of which depends on the contents and logic inside the includable files. - Probing of the existence of arbitrary directories on the server, which can allow attackers to fingerprint the server and site setup, including installed plugins and the content structure. ### Patches The problem has been patched in [Kirby 5.4.1](https://github.com/getkirby/kirby/releases/tag/5.4.1). Please update to this or a [later version](https://github.com/getkirby/kirby/releases) to fix the vulnerability. In the mentioned release, Kirby has added additional checks to the user lookup that ensure that the provided user ID only contains valid characters and that the resulting path to the account directory is contained in the `site/accounts` directory. ### Credits Kirby thanks @offset for responsibly reporting the identified issue.

### TL;DR This vulnerability affects all Kirby sites on Kirby 5.3.0-5.4.0 and is independent from setup conditions and authentication. **This vulnerability is of high severity for all Kirby sites**. ---- ### Introduction Path traversal is a type of attack that allows to access arbitrary filesystem paths. By using special elements such as `..` and `/` separators, attackers can escape outside of the restricted location to access files or directories that are elsewhere on the system. One of the most common special elements is the `../` sequence, which in most modern operating systems is interpreted as the parent directory of the current location. Path traversal can give attackers information about the filesystem and directory structure on the server and can lead to additional attacks depending on the nature of the accessible files and directories. PHP file inclusion is a type of attack that allows to load and execute PHP files on the server that are not intended for direct inclusion. Depending on the logic inside the PHP files, this can lead to disclosure of sensitive information or unintended, malicious actions. ### Affected components Kirby's `Users` collection received a performance improvement in Kirby 5.3.0. Starting in this release, Kirby loads user objects lazily when they are first needed. Users are queried by their user ID, which is then used to look up the user's account directory in the `site/accounts` directory. This applies to the authentication API (accessible to unauthenticated requests), the users API (accessible to authenticated users only) as well as to other places that use `$users->find()` to look up an individual user with a request-provided email or user ID. ### Impact In affected releases, Kirby did not correctly validate the provided user ID, causing a path traversal vulnerability. This vulnerability results in the following impact: - Arbitrary PHP file inclusion of files with the filename `index.php` (e.g. the main PHP files of plugins), the impact of which depends on the contents and logic inside the includable files. - Probing of the existence of arbitrary directories on the server, which can allow attackers to fingerprint the server and site setup, including installed plugins and the content structure. ### Patches The problem has been patched in [Kirby 5.4.1](https://github.com/getkirby/kirby/releases/tag/5.4.1). Please update to this or a [later version](https://github.com/getkirby/kirby/releases) to fix the vulnerability. In the mentioned release, Kirby has added additional checks to the user lookup that ensure that the provided user ID only contains valid characters and that the resulting path to the account directory is contained in the `site/accounts` directory. ### Credits Kirby thanks @offset for responsibly reporting the identified issue.