CVE-2026-55474: Snipe-IT vulnerable to directory traversal in displaySig

The displaySig action in ActionlogController serves signature image files from a private upload directory. The filename parameter from the HTTP route is concatenated directly into a filesystem path with no sanitization, allowing an authenticated attacker to traverse outside the intended directory and read arbitrary files accessible to the web server process.

Reported by https://github.com/securin-public