Criminals have started targeting hospitals and schools with ransomware, using vulnerabilities in popular application servers to infiltrate organizations' networks and to insert backdoors to allow access, according to an analysis by networking giant Cisco.
In a scan of the Internet, the company found that more than 3.2 million computers running the popular JBoss application server are likely at risk of being attacked. Already, some 2,100 servers hosted at 1,600 Internet addresses show signs of being infected by a testing and exploitation tool known as JexBoss, which enables backdoor access to a compromised JBoss system.
Once compromised, the servers are often infected with a ransomware program known as Samsam.
"I think it is very much a target of opportunity," said Matt Olney, manager of threat intelligence analytics of Cisco's Talos group. "I don't think the educational sector was being targeting specifically; they happen to be running JBoss and they got caught up in this activity."
While schools and healthcare facilities have been hacked in the past, ransomware infections are less common. Over the past year, however, crypto-ransomware attacks have become more frequent, hitting businesses, consumers, government offices, schools and, most recently, hospitals.
Most ransomware relies on tricking a user into running a program that infects the victim's system. Samsam, however, infects servers directly using a year-old vulnerability that became widely known in November.
The vulnerability occurs in the way that some application servers—including JBOSS, WebSphere and Weblogic—handle the conversion of data objects in Java, known as unserialization.
Once attackers get control of a server through the vulnerability, they load JexBoss onto the server to allow easy access through the backdoor program. The attackers then use the backdoor to install Samsam.
In some cases, the attackers have been known to install denial-of-service tools and Bitcoin mining tools. The attackers often reconnoiter the network to find more potential victims for their software.
The attackers installing the JexBoss backdoor and the Samsam malware may not be the same group, Olney said.
"We've seen multiple people use the same backdoor on a particular system," he said. "The Samsam actor is likely using some pre-existing backdoor to get into the system."
Cisco also warned the maker of a library management system that runs on JBoss that it appeared to be vulnerable to the flaws. The management system is often used by school libraries, the company said.
Once Samsam is installed, it requires no action by the operators. SamSam and another recent ransomware program known as Maktub do not require a connection to a command-and-control server to encrypt data on a targeted system.
Internet-connected JBoss servers still vulnerable to the Java unserialization flaw pose a serious hazard for the organizations that own the computers. Because anyone can scan for signs of the vulnerabilities, such servers are easy to target—and many attackers have, Cisco said.
"[W]e've learned that there is normally more than one webshell on compromised JBoss servers," the company stated in its post, adding that it has seen a variety of backdoors on the same server with names such as "mela," "shellinvoker," "jbossinvoker," "zecmd," "cmd," "genesis," and "sh3ll."
"This implies that that many of these systems have been compromised several times by different actors," the company said.