GHSA-fg79-cr9c-7369 OpenMage LTS: Phar Deserialization leads to Remote Code Execution

• Packagist openmage/magento-lts: < 20.17.0 → fixed in 20.17.0

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 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 /tmp/pwned'; function __destruct() { system($this->cmd); } } $phar = new Phar('exploit.phar'); $phar->startBuffering(); $phar->addFromString('test.txt', 'test'); $phar->setStub(''); $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 • ` 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 through HackerOne. Timeline • 2025-12-31: Vulnerability reported via HackerOne • 2026-01-21: Fix developed and tested Source: https://hackerone.com/reports/3482926