“Infected Word files being used to spread ransomware, security researchers say.
Cyber crooks, obviously buoyed by the growing success of their peers with using such malware, have been releasing more versions with alarming regularity. The newest one to join the increasingly crowded ranks of ransomware tools is “Locky,” a somewhat awkwardly named but just as dangerous tool as the ones already floating out there.
UK-based security researcher Kevin Beaumont, who was one of the first to report on the new strain, on Wednesday reported seeing around 4,000 new infections per hour, or roughly 100,000 per day. When initially spotted about four days ago, Locky was detectable by just three antivirus products from what Beaumont described as niche vendors. Since then security vendors have updated their signatures and most major AV products now detect the malware Beaumont said in a post last updated Wednesday.
Security researcher Lawrence Abrams, who has also been tracking Locky, described it as targeting a large number of file extensions on infected systems. “Even more importantly [it] encrypts data on unmapped network shares,” he said in a blog post on BleepingComputer.com.
“Encrypting data on unmapped network shares is trivial to code,” he said. The fact that another recent ransomware tool, dubbed DMA Locker, had the exact capability suggests this will become the norm going forward, he said. Locky is also similar to CryptoWall in that it changes the filenames for files it encrypts, making it harder to restore the right data, he added.
Locky is being distributed via a Microsoft Word attachment with malicious macros in it. Victims typically receive an email with an attached Word document purporting to be an invoice seeking payment for some product or service. Recipients who click on the attachment are presented with a document containing scrambled content and an instruction to click on an Office macro to unscramble it. Once enabled, the macro downloads Locky, stores it in the Temp folder and executes it.
Stu Sjouwerman, CEO of security vendor KnowBe4 said one way for enterprises to mitigate the risk is to disable all except digitally signed Office macros from running. If implemented correctly, users will not even see the prompt asking them to enable a macro when they click on the Word document attachment that is being used to distribute Locky, he said in a blog post outlining the steps security admins can take to disable macros.
Threat actors have been using ransomware tools like Locky to devastating effect recently. Just this week for instance, Hollywood Presbyterian Medical Center in Los Angeles said it was the victim of a ransomware attack that ended with it having to pay a ransom of $17,000 to get attackers to unlock the hospital data they had encrypted.
The success of these attacks suggest that the ransomware problem is not going anywhere soon says, Dodi Glenn, vice president of cybersecurity at PC Pitstop in comments to Dark Reading. “The actors behind [such attacks] are financially stable enough to continue to build newer versions of the malware. It is crucial to have important data backed up and stored offline in the event you are hit with ransomware,” he says.
Traditional blacklist antivirus engines have been having a hard time catching ransomware because malware authors are constantly changing portions of the code to remain undetected, he said. “Services like VirusTotal.com allow the hacker to upload newly created malware to see what any of the 54 different antivirus vendors say about the file. They will continue to tweak the file until no vendor detects it,” he said.”