AIKIDO-2026-999895

TL;DR

The file_system storage in shrine builds the full path to a file by joining the configured storage directory with the file id, without validating where the result resolves. When the id comes from attacker-controlled data, such as a tampered cached attachment hash containing ../ sequences, the path can resolve to a location outside of the storage directory. Operations like opening, deleting, checking existence, and uploading then act on arbitrary files on the host filesystem, allowing out-of-bounds file read and deletion. The fix raises Shrine::Error whenever an id would resolve outside of the storage directory.