Grav CMS before 2.0.13 contains a remote code execution vulnerability in the Flex Objects plugin settings validation that allows authenticated users to execute arbitrary code by uploading a ZIP file containing PHP code. Attackers can bypass routine name validation by using array notation instead of string notation, call the unZip routine with a malicious archive, and write PHP files to the web root for execution.

Affected: Packagist: getgrav/grav

### Summary

A logged-in user can run any command on the server. A settings field can fill itself by calling one of Grav's built-in routines, and a safety check is supposed to allow only harmless ones. The check only recognises a routine when its name is written as one piece of text; named as a pair of values instead, it is not examined at all and is passed as safe. Pointing such a field at the routine that unpacks ZIP archives writes a PHP file from an uploaded archive into the site's public folder, which the server then runs.

### Details

The check rejects known-dangerous routines and, for those belonging to a component, allows only a short approved list. Both of those cases only apply when the name arrives as a single string. The same routine can be named as a pair (the component and the routine inside it), and in that form the check matches neither case, skips both lists and answers "safe". Grav then calls it, with arguments the attacker supplies in the same field. Any routine shipped with Grav becomes callable.

The one used here is what Grav runs when installing a plugin from an archive. It takes an archive and a destination folder. It does check the names of the files inside, so an archive cannot escape with `../`, but the destination is used exactly as given, so naming the folder the website is served from drops the contents there. Getting the archive in is trivial: ZIP is an accepted upload type and the files inside are never examined, so an archive containing a PH…