CVE-2026-39369: WWBN AVideo's GIF poster fetch bypasses traversal scrubbing and exposes local files through public media URLs

WWBN AVideo is an open source video platform. In versions 26.0 and prior, objects/aVideoEncoderReceiveImage.json.php allowed an authenticated uploader to fetch attacker-controlled same-origin /videos/... URLs, bypass traversal scrubbing, and expose server-local files through the GIF poster storage path. The vulnerable GIF branch could be abused to read local files such as /etc/passwd or application source files and republish those bytes through a normal public GIF media URL.