Kirby is an open-source content management system. A vulnerability in versions prior to 3.9.8.3, 3.10.1.2, and 4.7.1 affects all Kirby sites that use the `collection()` helper or `$kirby->collection()` method with a dynamic collection name (such as a collection name that depends on request or user data). Sites that only use fixed calls to the `collection()` helper/`$kirby->collection()` method (i.e. calls with a simple string for the collection name) are *not* affected. A missing path traversal check allowed attackers to navigate and access all files on the server that were accessible to the PHP process, including files outside of the collections root or even outside of the Kirby installation. PHP code within such files was executed. Such attacks first require an attack vector in the site code that is caused by dynamic collection names, such as `collection('tags-' . get('tags'))`. It generally also requires knowledge of the site structure and the server's file system by the attacker, although it can be possible to find vulnerable setups through automated methods such as fuzzing. In a vulnerable setup, this could cause damage to the confidentiality and integrity of the server. The problem has been patched in Kirby 3.9.8.3, Kirby 3.10.1.2, and Kirby 4.7.1. In all of the mentioned releases, the maintainers of Kirby have added a check for the collection path that ensures that the resulting path is contained within the configured collections root. Collection paths that point outs…

Affected: Packagist: getkirby/cms

### TL;DR

This vulnerability affects all Kirby sites that use the `collection()` helper or `$kirby->collection()` method with a dynamic collection name (such as a collection name that depends on request or user data).

Sites that only use fixed calls to the `collection()` helper/`$kirby->collection()` method (i.e. calls with a simple string for the collection name) are *not* affected.

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### Introduction

Kirby's `collection()` helper and `$kirby->collection()` method (in the following abbreviated to the `collection()` helper) allow to load PHP logic files that are normally stored in the `site/collections` folder or registered by plugins through the `collections` plugin extension.

If the `collection()` helper is called with an arbitrary collection name, Kirby first checks if a file with this name exists in the collections root (which defaults to `site/collections`).

This logic was vulnerable against path traversal attacks. 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.

Because Kirby's `collection()` helper did not protect against path traversal, the provided collection name could include special sequences that would cause Kirby to look outside of the configured collections…