Here's how to stop most ransomware in its tracks: expert

Tighten controls on Web browsers and email, then use smart tools to detect and stop encryption activity

Despite its success, ransomware is relatively easy to detect and could be blocked in most cases if systems administrators took two simple steps, a Sophos security specialist has advised as the company debuted a tool designed to detect and stop new ransomware attacks in their tracks.

Continuous monitoring of access to files on the local computer offers telltale signs of ransomware activity when an application process begins scanning through a folder of files, Sophos principal research scientist Chet Wisniewski told CSO Australia.

Once the ransomware code begins encrypting files, he explained, “there is no way for the criminal to not dramatically increase the entropy of the files in that folder. If I have a folder of JPEGs, AutoCAD drawings or whatever, I can measure the entropy of a given file before and after a file operation; if I see the entropy rise dramatically, I know it's been encrypted.”

There are very few other legitimate processes that combine file scanning with high-entropy activity in the way that ransomware does, Wisniewski said, and the company's new Intercept X endpoint security tool whose CryptoGuard component applies “secret sauce” that filters out false positives by correlating file activity with specific behaviours in the operating-system kernel.

Even before the files are encrypted, the module backs up the files in high-activity folders and automatically rolls back those files to their last known state once the ransomware has been interrupted – providing seamless recovery of all files even if some have been encrypted. The toolset also includes a Root Cause Analytics (RCA) module that tracks the activity of rogue processes to allow security administrators to trace a new ransomware strain back from its activity to the process that spawned it.

Wisniewski believes the collective intelligence from RCA will give Sophos security researchers a progressively more-detailed view of ransomware activity that will help them better block future activities – as well as feeding threat-intelligence profiles that can guide end users towards taking proactive steps to block the possibility of new infections.

“This will give us a lot of insight,” he says. “If we can get a top 10 list of the things that put customers in harm's way, we can invest that much more in engineering solutions around those problems.”

Yet even before the tool-generated intelligence begins to produce results, Wisniewski says, there are two steps security administrators can take to eliminate the majority of ransomware “almost overnight” by blocking its preferred methods of attack.

First and foremost, administrators should eliminate Adobe Flash from users' Web browsers. “People feel we're losing this battle, but we're not,” he said.

“We're down to the point where Flash is literally the only reliable thing that criminals are exploiting on a daily basis to get through people's computers on the Web. If you can get rid of Flash you can move that off the table.”

The second protective measure is to block emails featuring JavaScript, which is used to launch all kinds of malware through inclusion as malicious attachments in emails. “We learned a long time ago not to allow .EXE files to be delivered via email, and criminals are now using JavaScript instead,” Wisniewski said.

“If you block JavaScript emails you'll get rid of almost all ransomware with just that one block. And if we could effectively communicate with people running email gateways out there to do this, we could have a big impact.”

Web browser authors have done “a great job” in tightening security holes and reducing dependence on potentially-buggy third-party plugins, Wisniewski added, noting that security administrators must also focus on educating users not to believe the claims in the emails they receive.

Intercept X is the latest in a string of tools claiming to be able to block ransomware, which has continued to explode in Australia and elsewhere where criminals see a potential financial return; one recent analysis suggested a single ransomware network was able to pull in $US121m ($160m) in ransomware payments. Newly discovered strains have explored different activities including deleting victims' files, integration with exploit kits, offline capabilities, exfiltrating and then deleting files from Linux Web servers, time-based increases in ransom, and exploitation of remote desktop protocol (RDP) connectivity.

In August, security firm SentinelOne said it would reimburse customers for up to $US1m ($A1.33m) if they were hit by a ransomware attack while using its defensive products. One security researcher has offered a free tool that blocks ransomware attacks on Macs, while other researchers have pointed out the value of better managing administrator rights and application access.