Ransomware

About DJVU (STOP) Ransomware (November 2019 Update)

Written by Brendan Smith

DJVU General information

DJVU cryptoware codifies the users’ data with the AES-256 algorithm (CFB mode). However, it does not encrypt the entire file, but rather approximately 5 MB in its beginning. Subsequently, it asks for the ransom that amounts to $980 in Bitcoin equivalent to restore the files.

The authors of the malware have Russian roots. The frauds use Russian language and Russian words written in English, as well as the domains registered through Russian domain-registration companies. The crooks most likely have allies in other countries.

DJVU Technical details

Many users indicate that the cryptoware is injected after downloading repackaged and infected installers of popular programs, pirated activators of MS Windows and MS Office (such as KMSAuto Net, KMSPico, etc.) distributed by the frauds through popular websites. This relates to both legitimate free applications and illegal pirated software.

The cryptoware may also be spread through hacking by means of poorly protected RDP configuration, via email spam and malicious attachments, misleading downloads, exploits, web injectors, faulty updates, repackaged and infected installers.

The list of file extensions subject for encryption:

MS Office or OpenOffice documents, PDF and text files, databases, photos, music, video or image files, archives, application files, etc.

Stages of cryptoware infection:

  1. Once launched, the cryptoware executable connects to the Command and Control server (С&C). Consequently, it obtains the encryption key and the infection identifier for the victim’s PC. The data is transferred under the HTTP protocol in the form of JSON.
  2. If С&C is unavailable (in times when the PC is not connected to the Internet of the server does not respond), the cryptoware applies the directly specified encryption key concealed in its code and performs the autonomous encryption. In this case, it is possible to decrypt the files without paying the ransom.
  3. The cryptoware uses rdpclip.exe to replace the legitimate Windows file and for implementing the attack on the computer network.
  4. Upon successful file encryption, the cipherer is autonomously removed by means of the delself.bat command file.

Associated Files:

%LocalAppData%\[guid]\[random_numbers]tmp.exe
%LocalAppData%\[guid]\1.exe
%LocalAppData%\[guid]\2.exe
%LocalAppData%\[guid]\3.exe
%LocalAppData%\[guid]\updatewin.exe
C:\Windows\System32\Tasks\Time Trigger Task

Associated Registry Entries:

HKCU\SOFTWARE\Microsoft\Windows\CurrentVersion\Run\SysHelper

Network Traffic:

api.2ip.ua
morgem.ru

In addition to encrypting a victim’s files, the DJVU family has also install the Azorult Spyware to steal account credentials, cryptocurrency wallets, desktop files, and more.

How to decrypt DJVU files?

Djvu Ransomware essentially has two versions.

  1. Old Version: Most older extensions (from “.djvu” up to “.carote (v154)”) decryption for most of these versions was previously supported by STOPDecrypter tool in case if infected files with an offline key. That same support has been incorporated into the new Emsisoft Decryptor for these old Djvu variants. The decrypter will only decode your files without submitting file pairs if you have an OFFLINE KEY.
  2. New Version: The newest extensions released around the end of August 2019 after the ransomware was changed. This includes .coharos, .shariz, .gero, .hese, .xoza, .seto, peta, .moka, .meds, .kvag, .domm, .karl, .nesa, .boot, etc….these new versions were supported only with Emsisoft Decryptor.

What is a “file pair”?

This is pair of files that are identical (as in they are the precise same data), except one duplicate is encrypted and the other is not.

How to identify offline or online key?

The SystemID/PersonalID.txt file created by STOP (DJVU) on your C drive contains all of the ID’s used in the encryption process.

Almost every offline ID ends with “t1”. Encryption by an OFFLINE KEY can be verified by viewing the Personal ID in the _readme.txt note and the C:\SystemID\PersonalID.txt file.

The quickest way to check if you were infected with an OFFLINE or ONLINE KEY is to:

  1. Find the PesonalID.txt file located in the folder C:\ SystemID\ on the infected machine and check to see if there is only one or multiple IDs.
  2. If the ID ends with “t1” there is a chance that some or your files were encrypted by the OFFLINE KEY and are recoverable.
  3. If none of the ID’s listed ends with “t1” then all of your files were most likely encrypted with an ONLINE KEY and are not recoverable at this time.
The full list of known DJVU files extension:

djvuu, uudjvu, blower, tfudet, promok, djvut, djvur, klope, charcl, doples, luces, luceq, chech, proden, drume, tronas, trosak, grovas, grovat, roland, refols, raldug, etols, guvara, browec, norvas, moresa, verasto, hrosas, kiratos, todarius, hofos, roldat, dutan, sarut, fedasot, forasom, berost, fordan, codnat, codnat1, bufas, dotmap, radman, ferosas, rectot, skymap, mogera, rezuc, stone, redmat, lanset, davda, poret, pidon, heroset, myskle, boston, muslat, gerosan, vesad, horon, neras, truke, dalle, lotep, nusar, litar, besub, cezor, lokas, godes, budak, vusad, herad, berosuce, gehad, gusau, madek, tocue, darus, lapoi, todar, dodoc, novasof, bopador, ntuseg, ndarod, access, format, nelasod, mogranos, nvetud, cosakos, kovasoh, lotej, prandel, zatrov, masok, brusaf, londec, kropun, londec

The list of STOP (DJVU) Ransomware.

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About the author

Brendan Smith

Journalist, researcher, web content developer, grant proposal editor. Efficient and proficient on multiple platforms and in diverse media. Computer technology and security are my specialties.

18 Comments

  1. vmph July 15, 2019
    • Brendan Smith July 15, 2019
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