Thousands of online shops powered by eBay’s Magento ecommerce platform could be vulnerable to hacker attacks due to a security hole in a popular third-party tool.

According to researchers at Trustwave, the vulnerability exists in Magmi, a mass importer tool that allows users to import a large number of products faster and more efficiently compared to the default system in Magento.

Magmi, developed as a Magento database client, is available for download on both GitHub and SourceForge, and while the versions offered on the two websites should be synchronized, experts discovered that the one from SourceForge includes a file (download_file.php) that makes Magento installations vulnerable to attacks.

The problem with “download_file.php” is that it opens a file specified in the request parameter without conducting the checks required to prevent directory traversal attacks. Since Magmi is usually installed on the server in the same folder as Magento, attackers can exploit the directory traversal vulnerability to access sensitive files.

Trustwave started seeing attacks exploiting this vulnerability last month. The HTTP requests observed by the security firm attempt to exploit the weakness to obtain Magento site credentials and database encryption keys.

“The vulnerability can only be exploited if the Magmi installation including the ‘\web’ location is not secured. It's best to protect Magmi wherever it resides using HTTP basic authentication or other methods,” Trustwave’s Assi Barak explained in a blog post. “If you installed Magmi without securing it, you're already vulnerable because credentials can be found in the Magmi UI admin pages. However, the directory traversal vulnerability in download_file.php makes the attack much easier to perform using a single GET request.”

As experts have pointed out, the Magmi version hosted on GitHub has been updated recently, but the version offered on SourceForge was last updated in December 2014. Considering that Magmi was downloaded from SourceForge nearly 30,000 times this year, a large number of websites could be vulnerable. Experts believe many users have downloaded Magmi from SourceForge because it’s the first result in a Google search for “magmi.”

After being alerted by Trustwave, Magento said it identified 1,700 apparently vulnerable websites, whose owners have been contacted. Sebastien Bracquemont, aka “dweeves,” the developer of Magmi, has also been notified, but the issue appears to remain unpatched.

The Magento platform is used by more than 240,000 merchants, which makes it a tempting target for malicious actors. In April, Check Point Software reported uncovering a critical flaw in Magento that could be leveraged to gain access to sensitive information, including payment card data. Experts noticed malicious attempts to exploit the vulnerability within 24 hours after disclosure.