Botnet Infects Hundreds of Thousands of Websites

A botnet focused on cryptomining, spamming, and defacement has infected hundreds of thousands of websites running popular content management systems (CMSes), such as WordPress, Joomla, Magneto, and Drupal, according to online security firm Imperva.

The botnet, dubbed KashmirBlack, uses a modular infrastructure that includes features such as load balancing communications with command-and-control servers and storing files on cloud storage services, such as Dropbox and GitHub, to speed access to any new code updates for the systems infected with the software. The KashmirBlack botnet mainly infects popular CMS platforms, exploiting dozens of known vulnerabilities on targeted servers and performing millions of attacks per day on average, according to a pair of reports published by Imperva researchers today.

CMSes are often not kept up-to-date and so can be exploited with public vulnerabilities, says Ofir Shaty, security analyst tech lead at Imperva and one of the authors of the reports. "The focus on content management systems is interesting," he says. "They chose something that would be easier to succeed at with exploitation, thus giving them the ability to increase the size of the botnet rapidly."

To gather information on the nearly year-old botnet, the researchers impersonated an infected server in the botnet and also created a honeypot server that ran one of the targeted CMS portals. The "spreading server" allowed the researchers to collect commands and scripts that were communicated to the botnet. When a compromised site was set to continue spreading the bot software, the researchers found it would attack an average of 240 hosts, or 3,450 victim sites, each day.

With 285 systems observed attempting to spread the bot software over several months, and an assumed success rate of 1%, the researchers estimated that some 230,000 sites had been compromised over the past 11 months.

"During our research we witnessed its evolution from a medium-volume botnet with basic abilities to a massive infrastructure that is here to stay," the researchers concluded in the reports.

The botnet's high-performance architecture, designed to make updating easy, made an impression on the researchers. The botnet uses two clusters of infected systems as repositories for code and exploits, and divides compromised systems into those actively seeking new bots and a larger group waiting for instructions. Load-balancing features were added to the repositories to increase responsiveness and availability, the researchers said. 

In addition, the botnet has quickly changed over the past 11 months. In September, for example, the botnet operators changed the command-and-control capability to use the Dropbox API to store logs of its operations and retrieve commands, the researchers noted in the reports. 

"The important thing here is to understand that botnet activity is dynamic," says Nadav Avital, head of threat research at Imperva. "It is not like you can block or put some security rule once and be done with it. The botnet evolves, it changes, it deploys new evasion techniques — sometimes every day, every week, or every month."

Using legitimate cloud services — the botnet also uses GitHub and Pastebin — makes the communications traffic harder to spot, says Imperva's Shaty.

"The botnet can easily camouflage itself in legitimate traffic," he says. "The services cannot detect it because the bot is just storing files. There are no malicious functionality."

Among the vulnerabilities exploited by the botnet are common weaknesses, such as systems that allow unrestricted upload of files, remote command execution, the ability to traverse the directory system, and a lack of limitations on credential attempts that enables brute-force password guessing. Many of the exploits target plug-ins for WordPress and other popular CMSes.

Most servers are tasked with either cryptomining or spamming, but in some cases the botnet appears to be used in some defacements. From one defacement signature, the researchers found a clue as to the botnet operator's identity: a hacker known as "Exect1337," who is a member of the Indonesian hacker crew "PhantomGhost."