This indicates an attack attempt against a Directory Traversal vulnerability in Joomla!.
The vulnerability is due to insufficient sanitizing of user supplied inputs in the application when handling a crafted HTTP request. Successful exploitation could lead to file access outside the media manager root directory.
Joomla! before 3.9.5
Information Disclosure: Remote attackers can gain sensitive information from vulnerable systems.
Apply the most recent upgrade or patch from the vendor.