GHSA-f4f9-627c-jh33 WWBN AVideo's GIF poster fetch bypasses traversal scrubbing and exposes local files through public media URLs

• Packagist WWBN/AVideo: <= 26.0 (no fix yet)

Summary `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. Details The vulnerable chain was: 1. `objects/aVideoEncoderReceiveImage.json.php` accepted attacker-controlled `downloadURL_gifimage` 2. traversal scrubbing used `str_replace('../', '', ...)`, which was bypassable with overlapping input such as `....//` 3. same-origin `/videos/...` URLs were accepted 4. `url_get_contents()` and `try_get_contents_from_local()` resolved the request into a local filesystem read 5. the fetched bytes were written into the GIF destination 6. invalid GIF cleanup used the wrong variable, so the non-image payload remained on disk This made the GIF poster path a local file disclosure primitive with public retrieval. Proof of concept 1. Log in as an uploader and create an owned video row through the normal encoder flow. 2. Send: ```text POST /objects/aVideoEncoderReceiveImage.json.php downloadURL_gifimage=https://localhost/videos/....//....//....//....//....//....//etc/passwd ``` 3. Query: ```text GET /objects/videos.json.php?showAll=1 ``` 4. Recover the generated GIF URL from `videosURL.gif.url`. 5. Download that GIF URL. 6. Observe that the body matches the target local file, such as `/etc/passwd`, byte-for-byte. Impact An authenticated uploader can read server-local files and republish them through a public GIF media URL by supplying a crafted same-origin `/videos/...` path to `downloadURL_gifimage`. Because traversal scrubbing was bypassable and the fetched bytes were written to the GIF destination without effective invalid-image cleanup, successful exploitation allows disclosure of files such as `/etc/passwd`, readable application source code, or deployment-specific configuration accessible to the application. Recommended fix • Reject any remote image URL whose decoded path contains traversal markers • Do not allow attacker-controlled same-origin `/videos/...` fetches to resolve into local file reads • Constrain any local shortcut path handling with `realpath()` and strict base-directory allowlists • Validate GIF content before saving it into public media storage • Ensure invalid-image cleanup checks the correct destination path