Security Experts:

Plesk Vulnerability Singled Out as Source of Massive Web Attack

Plesk, a popular Web hosting control panel – second to cPanel in the hosting market – was recently updated in order to address Remote File Inclusion vulnerabilities. This flaw is being blamed for a rash of website compromises, which successfully targeted some 50,000 domains.

Once attacked, the compromised domains would be used to host the Blackhole Exploit Kit, which would target visitors with various browser-based and host-based attacks. Each of the victimized domains shared a common thread; they were being managed by Plesk.

Plesk Vulnerability“I checked about a dozen of infected sites and they all use different web technologies from ASP.NET to pure HTML. They are all on different web servers: IIS, Litespeed, [or] Apache. The only common link I can see is Plesk,” explains a post on the Unmask Parasites blog.

When a Web hosting customer or website administrator develops a domain or a group of domains, they often use a control panel to make things easier. Control panels like Plesk or cPanel are the standard. For example, if you have a personal domain or a business domain from Media Temple – you use Plesk. If you use a service such as HostGator – you use cPanel.

When website owners started investigating their own incidents, the link to the vulnerability in Plesk became clear, and to make matters worse – it had been fixed months ago. The attackers were targeting the unpatched flaw from other compromised servers in order to hide themselves, but they likely scouted their targets long ago.

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“To make it more clear: Due to the Plesk vulnerability database tables could be read. And unfortunately all Passwords in Plesk are stored in plain text. Just fixing this vulnerability after the server has been compromised, without changing all passwords, leave valid username/password combinations! So the attacker can come back after weeks or months and attack even in the meantime updated Plesk systems,” the Unmask Parasites blog adds.

Plesk Versions 10.4 and earlier are impacted by this issue. Admins should ensure they have properly patched against the RFI flaw and changed all system passwords. Otherwise, the fix is not complete. To make matters worse, the vulnerability is being sold online, according to a post from security blogger Brian Krebs.

Instructions for checking for signs of compromise are here

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Steve Ragan is a security reporter and contributor for SecurityWeek. Prior to joining the journalism world in 2005, he spent 15 years as a freelance IT contractor focused on endpoint security and security training.