Mischa ransomware: decrypt files and remove the virus

The authors of the once widespread Petya ransomware have coined a new extortion tool that goes by another popular Russian name – Mischa. Whereas these two undoubtedly represent the same family and share some behavioral patterns, the latter is drastically different from its forerunner. The Mischa ransomware is a more ‘classic’ sample, because it encrypts the end user’s personal files rather than corrupting the Master File Table. This somewhat milder impact, which still allows the infected person to actually boot into Windows, doesn’t make the newcomer Trojan any less hazardous, though. It uses a cryptographic algorithm that’s strong enough to prevent data recovery through brute-forcing, which basically means that the victim runs the risk of losing all important files unless they pay up.

Mischa ransomware payment service site
Mischa ransomware payment service site

Having encrypted one’s data, the malady also appends a unique extension to filenames. Some examples of these strings are .9RWE, .aRpt, .3P7m, .eQTz, .cRh8, and .3RNu. The general pattern here is four symbols that include digits as well as lowercase and capitalized characters. Therefore, a file originally named ‘to-do list.doc’ may morph into something like ‘to-do list.doc.cRh8’ and will become inaccessible.

The Mischa virus also drops two new files into every affected system path and on the desktop. These are ransom instructions titled Your_Files_Are_Encrypted.html and Your_Files_Are_Encrypted.txt. The warning inside them is as follows: “You became victim of the MISCHA RANSOMWARE! The files on your computer have been encrypted with a military grade encryption algorithm. There is no way to restore your data without a special key. You can purchase this key on the darknet page shown in step 2.” The step being referred to recommends the user to visit one of the two available pages with the Tor browser, namely mischapuk6hym72.onion/[6 digits and chars] or mischa5xyix2mrhd.onion/[6 digits and chars]. On the Tor gateway, the victim is told to enter their personal decryption code provided in the ransom instructions and submit somewhere in the range of 1 BTC, or 400-500 USD, to the criminals to get the decryptor.

Malicious executable in the cloud
Malicious executable in the cloud

The Mischa ransomware operators stick with social engineering to distribute their Trojan. The would-be victims receive an email disguised as a job application. It’s noteworthy that the infection chiefly targets German users at this point. The message is titled “Bewerbung Zivildienst” and urges the recipient to click on a link to a page hosted on Magentacloud.de, a popular German cloud provider. The page contains two files: Bewerbungsfoto.jpg, which is the fake applicant’s photo; and PDFBewerbungsmappe.exe. Effectively, the criminals thus want the user to execute the malicious process, which in its turn launches the ransomware on the computer.

There is no automatic decrypt solution for Mischa ransomware as of the time of writing. However, what the compromised users should definitely try is a set of steps that may restore data via the Volume Shadow Copy Service, which is built into the operating system, or through the use of recovery software. And remember that paying the ransom supports cybercrime directly, so it’s best to give all alternative workarounds a shot.

This entry was posted in Guides. Bookmark the permalink.

Leave a Reply

Your email address will not be published. Required fields are marked *