A critical vulnerability in a popular e-commerce extension for the Joomla content management system allows malicious users to gain super-admin privileges to sites that run the software.The VirtueMart extension, which allows users to set up online shops on their websites, has been downloaded more than 3.5 million times, said Marc-Alexandre Montpas, a researcher at Web security firm Sucuri, in a blog post Wednesday. "With super-admin access, the attacker has full control of the site and database."The issue was discovered last week and was patched in VirtueMart 2.6.10, released on Sept. 4. The VirtueMart page in the Joomla extensions catalogue advises users that "everyone using a version lower than 2.6.10 should update as soon as possible for security reasons."Sucuri originally released technical details about the vulnerability, but then removed them at the developer's request because the issue might also affect other extensions."VirtueMart uses Joomla's JUser class 'bind' and 'save' methods to handle user accounts information," Montpas said. "That's not a problem in and of itself, but this class is very tricky and easy to make mistakes with. We actually think the problem is on the Joomla class itself, so we will not disclose any more details."The VirtueMart developers feel the same. They disapproved of Sucuri's decision to make the details public, calling it "amateurish" on Twitter and said that VirtueMart won't be the only component with the problem.The VirtueMart website contains a long list of online stores built with the extension and it will probably take some time until their owners update them all, putting the sensitive data stored in their databases at risk in the meantime."Great post, but can you perhaps nudge us a bit toward the location of the security risk," one user named Martijn Faber, wrote in a comment to Sucuri's blog post. "We currently have some projects in [VirtueMart] 2.6.8 which cannot be updated easily. We have to fix this by hand (line by line).""I have the same problem as Martijn, can you please give us some list of updated VM core files?" another user said.