CVE-2026-25524: Openmage Magento RCE Vulnerability

CVE-2026-25524 Overview

CVE-2026-25524 is an insecure deserialization vulnerability affecting OpenMage Magento Long Term Support (LTS), an unofficial, community-driven e-commerce platform that provides an alternative to Magento Community Edition with high backward compatibility. The vulnerability allows remote attackers to achieve arbitrary code execution by exploiting PHP's PHAR deserialization behavior during image validation and media handling operations.

Prior to version 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 on the server.

Critical Impact

This vulnerability enables unauthenticated remote code execution through PHAR deserialization, potentially allowing complete server compromise of affected OpenMage Magento LTS e-commerce installations.

Affected Products

• OpenMage Magento LTS versions prior to 20.17.0
• OpenMage Magento e-commerce platform (community-driven LTS releases)

Discovery Timeline

• April 20, 2026 - CVE-2026-25524 published to NVD
• April 23, 2026 - Last updated in NVD database

Technical Details for CVE-2026-25524

Vulnerability Analysis

The vulnerability stems from improper handling of file operations in OpenMage Magento LTS when processing uploaded media files. PHP's native file functions, including getimagesize(), file_exists(), and is_readable(), can trigger automatic deserialization when they encounter paths using the phar:// stream wrapper. This behavior exists because PHP's PHAR (PHP Archive) implementation processes the archive's metadata during these file operations, which includes deserializing any stored objects.

OpenMage LTS utilizes these vulnerable functions during image validation and media handling workflows without adequate protection against PHAR deserialization attacks. The CWE-502 (Deserialization of Untrusted Data) classification accurately describes this flaw, as the platform processes serialized data within PHAR files without verifying the integrity or safety of the objects being deserialized.

Root Cause

The root cause is the combination of two factors: PHP's automatic deserialization behavior when handling PHAR archives, and OpenMage LTS's use of file operation functions with user-controllable paths. When an attacker can influence the file path parameter passed to functions like getimagesize(), they can prepend phar:// to trigger deserialization of a previously uploaded malicious PHAR file.

The vulnerability is particularly dangerous because PHAR files can be crafted with valid image headers (polyglot files), allowing them to bypass basic image upload validation while containing malicious serialized PHP objects in their metadata section.

Attack Vector

The attack requires network access and follows a multi-step exploitation chain:

1. Malicious File Upload: The attacker uploads a specially crafted PHAR file disguised as a legitimate image (polyglot file) through the platform's media upload functionality
2. Path Manipulation: The attacker manipulates a request to cause OpenMage to process the uploaded file using a phar:// stream wrapper path
3. Deserialization Trigger: When PHP processes the phar:// path through functions like getimagesize(), it deserializes the malicious objects embedded in the PHAR metadata
4. Code Execution: The deserialized objects execute attacker-controlled code through PHP's magic methods or existing gadget chains in the application

The vulnerability can be exploited to achieve arbitrary PHP code execution, which typically allows complete server compromise including database access, customer data theft, and installation of persistent backdoors.

Detection Methods for CVE-2026-25524

Indicators of Compromise

• Unusual file uploads with mixed content types (files appearing as images but containing PHAR signatures)
• Web server logs showing requests with phar:// in URL parameters or POST data
• Unexpected PHP object serialization strings (O:) in uploaded media files
• Suspicious files in the media/ directory containing PHAR archive signatures (__HALT_COMPILER();)
• Error logs indicating deserialization failures or unexpected class instantiations

Detection Strategies

• Monitor web application logs for phar:// stream wrapper usage in request parameters
• Implement file upload scanning to detect polyglot files (files with mismatched magic bytes and extensions)
• Deploy web application firewall rules to block requests containing phar:// patterns
• Review uploaded media files for PHAR archive signatures and serialized object patterns
• Enable PHP error logging and monitor for deserialization-related exceptions

Monitoring Recommendations

• Configure security information and event management (SIEM) alerts for phar:// pattern detection
• Implement file integrity monitoring on the OpenMage media directories
• Monitor for unusual process spawning from the web server context
• Review access logs for sequential upload and access patterns that may indicate exploitation attempts

How to Mitigate CVE-2026-25524

Immediate Actions Required

• Upgrade OpenMage Magento LTS to version 20.17.0 or later immediately
• Audit existing uploaded media files for potential PHAR polyglot files
• Review web server logs for evidence of prior exploitation attempts
• Consider temporarily disabling media upload functionality if patching is delayed
• Implement web application firewall rules to block phar:// stream wrapper patterns

Patch Information

The OpenMage development team has released version 20.17.0 which addresses this PHAR deserialization vulnerability. The patch implements proper validation to prevent phar:// stream wrapper abuse during file operations. Administrators should upgrade to this version immediately.

For detailed patch information and release notes, see the GitHub Release v20.17.0 and the GitHub Security Advisory GHSA-fg79-cr9c-7369.

Workarounds

• Configure web server or WAF rules to block requests containing phar:// in any parameter
• Disable the PHAR stream wrapper in PHP configuration using stream_wrapper_unregister('phar') if PHAR functionality is not required
• Implement strict file upload validation that checks file contents match declared MIME types
• Restrict file upload capabilities to authenticated administrators only until patching is complete
• Consider PHP's phar.readonly=1 setting, though this does not fully mitigate the deserialization risk

# PHP configuration to disable PHAR stream wrapper (add to php.ini or .htaccess)
# Note: This is a workaround; upgrading to v20.17.0 is recommended
php_value phar.readonly 1

# Apache mod_rewrite rule to block phar:// requests
RewriteEngine On
RewriteCond %{QUERY_STRING} phar:// [NC,OR]
RewriteCond %{REQUEST_URI} phar:// [NC]
RewriteRule .* - [F,L]