GHSA-fg79-cr9c-7369

PHP functions such as `getimagesize()`, `file_exists()`, and `is_readable()` can trigger deserialization when processing `phar://` stream wrapper paths. OpenMage LTS uses these functions with potentially controllable file paths during image validation and media handling. An attacker who can upload a malicious phar file (disguised as an image) and trigger one of these functions with a `phar://` path can achieve arbitrary code execution. | Metric | Value | Justification | | ------------------------ | --------- | ------------------------------------------------ | | Attack Vector (AV) | Network | Exploitable via file upload and web requests | | Attack Complexity (AC) | High | Requires file upload + triggering phar:// access | | Privileges Required (PR) | None | Some upload vectors don't require authentication | | User Interaction (UI) | None | Exploitation is automatic once triggered | | Scope (S) | Unchanged | Impacts the vulnerable component | | Confidentiality (C) | High | Full system access via RCE | | Integrity (I) | High | Arbitrary code execution | | Availability (A) | High | Complete system compromise possible | ## Affected Products - OpenMage LTS versions < 20.16.1 - All versions derived from Magento 1.x with these code paths ## Affected Files | File | Line | Vulnerable Function | | --------------------------------------------------------- | ---- | ---------------------------------------------- | | `app/code/core/Mage/Core/Model/File/Validator/Image.php` | 72 | `getimagesize($filePath)` | | `app/code/core/Mage/Cms/Model/Wysiwyg/Images/Storage.php` | 137 | `getimagesize($item->getFilename())` | | `lib/Varien/Image.php` | 71 | `$this->_getAdapter()->open($this->_fileName)` | ## Vulnerability Details PHP's phar (PHP Archive) format stores metadata that is serialized. When PHP's stream wrapper functions access a file using the `phar://` protocol, the metadata is automatically deserialized. This occurs even with seemingly safe functions like `file_exists()` or `getimagesize()`. A polyglot file can be crafted that is both a valid image (passing initial validation) and a valid phar archive containing malicious serialized objects. When the application later processes this file using `phar://`, the deserialization triggers a gadget chain leading to RCE. ### Attack Flow 1. **Create polyglot file**: Attacker creates a file that is both valid JPEG and valid PHAR 2. **Upload file**: Attacker uploads the polyglot via product images, CMS media, or import 3. **Trigger phar:// access**: Attacker causes the application to access the file using `phar://` wrapper 4. **Code execution**: PHAR metadata deserialization triggers gadget chain ### Proof of Concept ```php <?php // Create malicious phar file class ExploitGadget { public $cmd = 'id > /tmp/pwned'; function __destruct() { system($this->cmd); } } $phar = new Phar('exploit.phar'); $phar->startBuffering(); $phar->addFromString('test.txt', 'test'); $phar->setStub('<?php __HALT_COMPILER(); ?>'); $phar->setMetadata(new ExploitGadget()); $phar->stopBuffering(); // Rename to appear as image rename('exploit.phar', 'exploit.jpg'); // When getimagesize('phar://path/to/exploit.jpg') is called, // the ExploitGadget::__destruct() method executes ``` ## Remediation Block `phar://` paths before passing to vulnerable functions: ```php // Before (vulnerable) [$imageWidth, $imageHeight, $fileType] = getimagesize($filePath); // After (fixed) if (str_starts_with($filePath, 'phar://')) { throw new Exception('Invalid image path.'); } [$imageWidth, $imageHeight, $fileType] = getimagesize($filePath); ``` Additionally, ICO files (which cannot be re-encoded by GD) are now scanned for phar signatures: - `__HALT_COMPILER();` - Required phar stub - `<?php` - PHP opening tag - `<?=` - PHP short echo tag Additional hardening measures: 1. **ICO uploads removed**: ICO file support is completely removed from new image uploads. This eliminates the polyglot attack vector entirely since all other image formats are re-encoded by GD, which strips any embedded phar metadata. 2. **Phar wrapper disabled**: The `phar://` stream wrapper is unregistered at application bootstrap, preventing any phar deserialization attacks regardless of code path. 3. **Cache deserialization hardening**: All `unserialize()` calls on cached data now use `allowed_classes => false` as defense-in-depth. **Note:** Existing uploaded ICO files will continue to work. Only new ICO uploads will be rejected. Users are encouraged to use PNG favicons for new uploads. ## Workarounds If immediate upgrade is not possible: 1. **Disable phar stream wrapper** (if not needed): ```ini ; php.ini disable_functions = phar:// ``` Or in code: ```php stream_wrapper_unregister('phar'); ``` 2. **Strict upload validation**: Implement additional validation beyond file extension 3. **File storage isolation**: Store uploads outside web root with randomized names 4. **Web Application Firewall**: Block requests containing `phar://` in parameters ## Credit This vulnerability was discovered and responsibly disclosed by [blackhat2013](https://hackerone.com/blackhat2013) through HackerOne. ## Timeline - **2025-12-31**: Vulnerability reported via HackerOne - **2026-01-21**: Fix developed and tested Source: https://hackerone.com/reports/3482926