As ransomware authors continue to increase their presence on the threat landscape, the group behind the DMA Locker malware is getting ready for massive distribution, Malwarebytes researchers warn.
DMA Locker is a piece of ransomware that was detailed for the first time early this year, when it was unstable and rather easy to counter. At the time, researchers discovered samples that would crash after completing the encryption process and concluded that it wasn’t much of a threat, mainly because it didn’t employ automated distribution.
Version 1 of DMA Locker used an in-house, rather weak encryption method and had no defenses against anti-malware analysis. Furthermore, the malware called API functions via plain text and included debug strings that described its activities. Unlike other ransomware in the wild, this threat didn’t include a list of targeted extensions, but two blacklists, one for folders and the other for extensions.
Fast-forward to today, when version 4.0 of DMA Locker is now lurking, and employs a multitude of improvements, including a better encryption and a new distribution technique that might signal an impending outbreak.
The DMA Locker authors have been very busy over the past several months, transforming their offspring into a more complex threat, no longer easily decryptable, and also using the Neutrino exploit kit (EK) for distribution (previous versions were distributed via hacked Remote Desktops). As Malwarebyte’s Hasherezade explains, this maturing threat appears ready to be spread on a wider scale than before.
The new DMA Locker variant uses an icon pretending to be a PDF document, but the main change is that it no longer encrypts files offline, but downloads the public RSA key from its command and control (C&C) server instead. This also means that the ransomware would not encrypt files on a compromised computer until Internet connection is available.
On the infected machine, the malware moves itself to C:ProgramData under the name svchosd.exe, where it also places two additional files, select.bat and cryptinfo.txt. The malware adds registry keys for persistency (Windows Firewall for svchosd.exe and Windows Update for select.bat). When the encryption process has been completed, it displays a red ransom window that displays the version in the top-left corner, allows users to decrypt a test file, and contains a link to a tutorial.
Unlike other ransomware, DMA Locker 4.0 directs victims to a website that is not Tor-based, but on a normal hosting, and which uses the same IP for the C&C server as well. However, Hasherezade suggests that the website is still a work in progress, while revealing that the test file decryption service offered on the website is not working properly.
The new ransomware version uses an individual AES key for each and every encrypted file, then encrypts this key using the RSA key fetched from the C&C server and appends it to the file. DMA Locker 4.0 is packed using an underground crypter, in an attempt to keep the payload protected and to avoid detection, and has automated the payment management, the security researcher notes.
Since the beginning of this year, DMA Locker has received numerous quality improvements and continues to evolve.
“The recently observed changes suggest that the product is preparing to be distributed on a massive scale. Few important things got automated. Distribution is now exploit kit based – that makes it reach much more targets. Purchasing a key and managing payment is supported via dedicated panel – no longer human interaction is required,” Hasherezade concluded.
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