FileRun before 2026.3.0 contains an OS command injection vulnerability in the PhotoProofSheet handler that allows authenticated users with upload permission to execute arbitrary commands by uploading files with shell metacharacters in their names. Attackers can upload a file containing command substitution syntax such as backticks, semicolons, or $() sequences in the filename, then trigger the PhotoProofSheet endpoint to execute arbitrary commands as the web-server user due to missing escapeshellarg() sanitization in the ImageMagick montage command construction.