Avast Releases Decryptor for the Prometheus Ransomware. Prometheus is a ransomware strain written in C# that inherited a lot of code from an older strain called Thanos.

Skip to how to use the Prometheus ransomware decryptor. 

How Prometheus Works

Prometheus tries to thwart malware analysis by killing various processes like packet sniffing, debugging or tools for inspecting PE files. Then, it generates a random password that is used during the Salsa20 encryption. 

Prometheus looks for available local drives to encrypt files that have one of the following  extensions:

db dbf accdb dbx mdb mdf epf ndf ldf 1cd sdf nsf fp7 cat log dat txt jpeg gif jpg png php cs cpp rar zip html htm xlsx xls avi mp4 ppt doc docx sxi sxw odt hwp tar bz2 mkv eml msg ost pst edb sql odb myd php java cpp pas asm key pfx pem p12 csr gpg aes vsd odg raw nef svg psd vmx vmdk vdi lay6 sqlite3 sqlitedb java class mpeg djvu tiff backup pdf cert docm xlsm dwg bak qbw nd tlg lgb pptx mov xdw ods wav mp3 aiff flac m4a csv sql ora dtsx rdl dim mrimg qbb rtf 7z 

Encrypted files are given a new extension .[ID-<PC-ID>].unlock. After the encryption process is completed, Notepad is executed with a ransom note from the file UNLOCK_FILES_INFO.txt informing victims on how to pay the ransom if they want to decrypt their files.

How to use the Avast decryptor to decrypt files encrypted by Prometheus Ransomware

To decrypt your files, follow these steps:

1. Download the free Avast decryptor.
2. Run the executable file. It starts in the form of a wizard, which leads you through the configuration of the decryption process.
3. On the initial page, you can read the license information, if you want, but you really only need to click “Next”.

4. On the next page, select the list of locations you want to be searched and decrypted. By default, it contains a list of all local drives:

5. On the third page, you need to provide a file in its original form and encrypted by the Prometheus ransomware. Enter both names of the files. In case you have an encryption password created by a previous run of the decryptor, you can select the “I know the password for decrypting files” option:

6. The next page is where the password cracking process takes place. Click “Start” when you are ready to start the process. During the password cracking process, all your available processor cores will spend most of their computing power to find the decryption password. The cracking process may take a large amount of time, up to tens of hours. The decryptor periodically saves the progress and if you interrupt it and restart the decryptor later, it offers you the option to resume the previously started cracking process. Password cracking is only needed once per PC – no need to do it again for each file.

7. When the password is found, you can proceed to decrypt all encrypted files on your PC by clicking “Next”.

8. On the final page, you can opt-in to backup encrypted files. These backups may help if anything goes wrong during the decryption process. This option is turned on 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.

IOCs

SHA256	File Extension
742bc4e78c36518f1516ece60b948774990635d91d314178a7eae79d2bfc23b0	.[ID-<HARDWARE_ID>].unlock

The post Decrypted: Prometheus Ransomware appeared first on Avast Threat Labs.

On February 24th, the Avast Threat Labs discovered a new ransomware strain accompanying the data wiper HermeticWiper malware,  which our colleagues at ESET found circulating in the Ukraine. Following this naming convention, we opted to name the strain we found piggybacking on the wiper, HermeticRansom. According to analysis done by Crowdstrike’s Intelligence Team, the ransomware contains a weakness in the crypto schema and can be decrypted for free.

If your device has been infected with HermeticRansom and you’d like to decrypt your files, click here to skip to the How to use the Avast decryptor to recover files

Go!

The ransomware is written in GO language. When executed, it searches local drives and network shares for potentially valuable files, looking for  files with one of the extensions listed below (the order is taken from the sample):

.docx .doc .dot .odt .pdf .xls .xlsx .rtf .ppt .pptx .one.xps .pub .vsd .txt .jpg .jpeg .bmp .ico .png .gif .sql.xml .pgsql .zip .rar .exe .msi .vdi .ova .avi .dip .epub.iso .sfx .inc .contact .url .mp3 .wmv .wma .wtv .avi .acl.cfg .chm .crt .css .dat .dll .cab .htm .html .encryptedjb

In order to keep the victim’s PC operational, the ransomware avoids encrypting files in Program Files and Windows folders.

For every file designated for encryption, the ransomware creates a 32-byte encryption key. Files are encrypted by blocks, each block has 1048576 (0x100000) bytes. A maximum of nine blocks are encrypted. Any data past 9437184 bytes (0x900000) is left in plain text. Each block is encrypted by AES GCM symmetric cipher. After data encryption, the ransomware appends a file tail, containing the RSA-2048 encrypted file key. The public key is stored in the binary as a Base64 encoded string:

Encrypted file names are given extra suffix:

.[[email protected]].encryptedJB

When done, a file named “read_me.html” is saved to the user’s Desktop folder:

There is an interesting amount of politically oriented strings in the ransomware binary. In addition to the file extension, referring to the re-election of Joe Biden in 2024, there is also a reference to him in the project name:

During the execution, the ransomware creates a large amount of child processes, that do the actual encryption:

How to use the Avast decryptor to recover files

To decrypt your files, please, follow these steps:

1. Download the free Avast decryptor.
2. Simply run the executable file. It starts in the form of a wizard, which leads you through the configuration of the decryption process.
3. On the initial page, you can read the license information, if you want, but you really only need to click “Next“

4. On the next page, select the list of locations which you want to be searched and decrypted. By default, it contains a list of all local drives:

5. On the final wizard page, you can opt-in whether you want to backup encrypted files. These backups may help if anything goes wrong during the decryption process. This option is turned on by default, which we recommend. After clicking “Decrypt”, the decryption process begins. Let the decryptor work and wait until it finishes.

IOCs

SHA256: 4dc13bb83a16d4ff9865a51b3e4d24112327c526c1392e14d56f20d6f4eaf382

The post Help for Ukraine: Free decryptor for HermeticRansom ransomware appeared first on Avast Threat Labs.