Decrypted: DoNex Ransomware and its Predecessors

Researchers from Avast have discovered a flaw in the cryptographic schema of the DoNex ransomware and its predecessors. In cooperation with law enforcement organizations, we have been silently providing the decryptor to DoNex ransomware victims since March 2024. The  cryptographic weakness was made public at Recon 2024 and therefore we have no reason to keep this secret anymore.

DoNex and its Brothers

The DoNex ransomware has been rebranded several times. The first brand, called Muse, appeared in April 2022. Multiple evolutions followed, resulting in the final version of the ransomware, called DoNex. Since April 2024, DoNex seems to have stopped its evolution, as we have not detected any new samples since. Additionally,  the TOR site of the ransomware has been down since that point. The following is a brief history of DoNex.

All brands of the DoNex ransomware are supported by the decryptor.

DoNex uses targeted attacks on its victims and it was most active in the US, Italy, and the Netherlands based on our telemetry.

Ransomware Encryption Schema

During the ransomware execution, an encryption key is generated by CryptGenRandom() function. This key is then used to initialize ChaCha20 symmetric key and subsequently to encrypt files. After a file is encrypted, the symmetric file key is encrypted by RSA-4096 and appended to the end of the file. The files are picked by their extension, and file extensions are listed in the ransomware XML config.

For small files (up to 1 MB), the entire file is encrypted. For files with size greater than 1 MB, intermittent encryption is used – the file is split into blocks and those blocks are encrypted separately.

Ransomware Configuration

Samples of the DoNex ransomware, and its previous versions, contain XOR-encrypted configuration, which contains settings of whitelisted extensions, whitelisted files, services to kill, and other encryption-related data. The following snippet shows a part of such configuration:

<?xml version='1.0' encoding='UTF-8'?>
<root>
    <white_extens>
        386;adv;ani;bat;bin;cab;cmd;com;cpl;cur;deskthemepack;diagcab;diagcfg;
        diagpkg;dll;drv;exe;hlp;icl;icns;ico;ics;idx;lnk;mod;mpa;msc;msp;msstyles;
        msu;nls;nomedia;ocx;prf;ps1;rom;rtp;scr;shs;spl;sys;theme;themepack;wpx;
        lock;key;hta;msi;pdb;search-ms
    </white_extens>
    <white_files>
        bootmgr;autorun.inf;boot.ini;bootfont.bin;bootsect.bak;desktop.ini;iconcache.db;
        ntldr;ntuser.dat;ntuser.dat.log;ntuser.ini;thumbs.db;GDIPFONTCACHEV1.DAT;d3d9caps.dat
    </white_files>
    <white_folders>
        $recycle.bin;config.msi;$windows.~bt;$windows.~ws;windows;boot;program files;
        program files (x86);programdata;system volume information;tor browser;windows.old;
        intel;msocache;perflogs;x64dbg;public;all users;default;microsoft;appdata
    </white_folders> 
    <kill_keep>
        sql;oracle;mysq;chrome;veeam;firefox;excel;msaccess;onenote;outlook;powerpnt;winword;wuauclt
    </kill_keep>
    <services>
        vss;sql;svc$;memtas;mepocs;msexchange;sophos;veeam;backup;GxVss;GxBlr;GxFWD;GxCVD;GxCIMgr
    </services>
    <black_db>
        ldf;mdf
    </black_db>
    <encryption_thread>
        30
    </encryption_thread>
    ...Code language: HTML, XML (xml)

How do I know if I have been attacked by DoNex ransomware?

The simplest way to identify that you have been attacked by the DoNex ransomware is the ransom note. Different brands of the DoNex ransomware produce a different ransom note, but every version contains a note. That said, the ransom note layout of the Fake LockBit, DarkRace and DoNex ransomwares are very similar. Below you can see examples of each.

How to use the DoNex ransomware decryptor

1. Download the decryptor here.
2. Run the executable file, preferably as an administrator. It starts as a wizard, leading you through the configuration of the decryption process.
3. On the initial page, we have a link to the license information. Click the Next button when you are ready to start.

4. On the next page, the user is asked to provide a list of locations (drives, folders, files) that are to be decrypted. By default, it has a list of all local disk drives.

5. On the following page, you need to supply an example of a file in its original form and then one encrypted by any brand of the DoNex ransomware. Type both names of the files. You can also drag & drop files from Windows Explorer to the wizard page. It is extremely important to pick a pair of files that are as big as you can find. The largest file size that is decryptable by the tool equals to the file size of the encrypted file in the pair.

6. The next page is where the password cracking process takes place. Click Start when you are ready to begin. This process usually only takes a second, but requires a large amount of system memory. This is why we strongly recommend using the 64-bit version of the decryption tool.
Once the password is found, you can continue to decrypt all the encrypted files on your PC by clicking Next.

7. On the final page, you can opt-in to back up your encrypted files. These backups may help if anything goes wrong during the decryption process. This choice is selected by default, which we recommend. After clicking Decrypt the decryption process begins. Let the decryptor work and wait until it finishes decrypting all of your files.

Indicators of Compromise (IOCs)