A piece of malware designed to launch brute-force password guessing attacks against websites built with popular content management systems like WordPress and Joomla has started being used to also attack email and FTP servers.
The malware is known as Fort Disco and was documented in August by researchers from DDoS mitigation vendor Arbor Networks who estimated that it had infected over 25,000 Windows computers and had been used to guess administrator account passwords on over 6,000 WordPress, Joomla and Datalife Engine websites.
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Once it infects a computer, the malware periodically connects to a command and control (C&C) server to retrieve instructions, which usually include a list of thousands of websites to target and a password that should be tried to access their administrator accounts.
The Fort Disco malware seems to be evolving, according to a Swiss security researcher who maintains the Abuse.ch botnet tracking service. "Going down the rabbit hole, I found a sample of this particular malware that was brute-forcing POP3 instead of WordPress credentials," he said Monday in a blog post.
The Post Office Protocol version 3 (POP3) allows email clients to connect to email servers and retrieve messages from existing accounts.
The C&C server for this particular Fort Disco variant responds with a list of domain names accompanied by their corresponding MX records (mail exchanger records). The MX records specify which servers are handling email service for those particular domains.
The C&C server also supplies a list of standard email accounts -- usually admin, info and support -- for which the malware should try to brute force the password, the Abuse.ch maintainer said.
"While speaking with the guys over at Shadowserver [an organization that tracks botnets], they reported that they have seen this malware family bruteforcing FTP credentials using the same methodology," he said.
Brute-force password guessing attacks against websites using WordPress and other popular CMSes are relatively common, but they are usually performed using malicious Python or Perl scripts hosted on rogue servers, the researcher said. With this malware, cybercriminals created a way to distribute their attacks across a large number of machines and also attack POP3 and FTP servers, he said.