The following hashes are relevant to this new variant:

Name: down.txt
URL: http://58.221.158[.]90:88/car/down.txt
Purpose: Downloader
MD5: 680d9c8bb70e38d3727753430c655699
SHA1: 5e72192360bbe436a3f4048717320409fb1a8009
SHA256: ddfd1d60ffea333a1565b0707a7adca601dafdd7ec29c61d622732117416545f
Compilation timestamp: 2020-01-11 19:04:24
VirusTotal report:
ddfd1d60ffea333a1565b0707a7adca601dafdd7ec29c61d622732117416545f

down.txt is, as mentioned, the downloader for the spreader module and for the actual ransomware:

Name: c.dat
URL: http://58.221.158[.]90:88/car/c.dat
Purpose: spreader
MD5: 01a9b1f9a9db526a54a64e39a605dd30
SHA1: a436e3f5a9ee5e88671823b43fa77ed871c1475b
SHA256: 9a1365c42f4aca3e9c1c5dcf38b967b73ab56e4af0b4a4380af7e2bf185478bc
Compilation timestamp: 2020-01-11 19:19:54
VirusTotal report:
9a1365c42f4aca3e9c1c5dcf38b967b73ab56e4af0b4a4380af7e2bf185478bc

Name: cpt.dat
URL: http://58.221.158[.]90:88/car/cpt.dat
Purpose: ransomware
MD5: 853358339279b590fb1c40c3dc0cdb72
SHA1: 84825801eac21a8d6eb060ddd8a0cd902dcead25
SHA256: ca154fa6ff0d1ebc786b4ea89cefae022e05497d095c2391331f24113aa31e3c
Compilation timestamp: 2020-01-11 19:54:25
VirusTotal report:
ca154fa6ff0d1ebc786b4ea89cefae022e05497d095c2391331f24113aa31e3c
Fun fact: file version information contains "TODO: 5SS5C Encoder".

The compilation times are sequential, which makes sense - the downloader has been developed (and compiled) first, then the spreader and the actual ransomware.

Note that cpt.exe as filename has already been observed in Satan ransomware.

Further indicators, such as hashes, URLs, file paths and so on will be posted at the end of this blog post.

• There are several logs created, e.g. there is a file "C:\Program Files\Common Files\System\Scanlog" that simply logs whether IPC SMB is open/available;
• Certutil logging (successful download or not);
• There are several Satan ransomware artefacts;
• Other Tactics, Techniques and Procedures (TTP) align with both Satan (and DBGer), and slightly overlap with Iron: 
• One of these is, for example, the use of multiple packers to protect their droppers and payloads. 
• This time however, they decided to use both MPRESS and Enigma, and even Enigma VirtualBox! (Note: Enigma and Enigma VirtualBox are not the same - the latter is a virtualised packer and also referred to as EnigmaVM.)

• ecology.url
• ecology.password
• ecology.user

What else is new is, as mentioned before, the use of Enigma VirtualBox for packing an additional spreader module, aptly named poc.exe. This suggest they may be experimenting (poc often is an acronym for proof of concept).

This file will be dropped to C:\ProgramData\poc.exe and will run the following command:

cd /D C:\ProgramData&star.exe --OutConfig a --TargetPort 445 --Protocol SMB --Architecture x64 --Function RunDLL --DllPayload C:\ProgramData\down64.dll --TargetIp 

Now compare this to Satan ransomware's command:

cmd /c cd /D C:\Users\Alluse~1\&blue.exe --TargetIp & star.exe --OutConfig a --TargetPort 445 --Protocol SMB --Architecture x64 --Function RunDLL --DllPayload down64.dll --TargetIp 

Something looks similar here... :-)

5ss5c ransomware - how it operates

• SSSS_Scan (in previous iterations SSS_Scan has also been observed)
• 5ss5c_CRYPT

Just like its predecessor, 5ss5c also has an exclusion list, where it will not encrypt specific files as well as files in the following folders:

Figure 4 - Exclusion list

Some files have been encrypted
If you want to retrieve the encrypted file, send (1) Bitcoins to my wallet
If payment is not completed within 48 hours from the start of encryption, the amount of decryption will double.
If you have other questions, you can contact me by email
Your decryption credentials are:

Email: [[email protected]]

Interestingly, the ransomware note does not contain a Bitcoin address. Additionally, the note only contains instructions in Chinese, not Korean nor English like previous iterations. Is 5ss5c ransomware more targeted, or just actively being tested by the group/developers behind it?

Encrypted files will have the actor's email address prepended and a unique token with the ransomware's name will be appended, for example;
test.txt becomes [[email protected]]test.txt.Y54GUHKIG1T2ZLN76II9F3BBQV7MK4UOGSQUND7U.5ss5c.

Prevention

Conclusion

Satan is dead, long live 5ss5c! It just doesn't sound as good, does it?

Whoever's behind the development of Satan, DBGer, Lucky and likely Iron ransomware, is back in business with the 5ss5c ransomware, and it appears to be in active development - and is trying to increase (or perhaps focus?) its targeting and spread of the ransomware.

It is recommended organisations detect and/or search for the indicators of compromise (IOCs) below, and have proper prevention controls in place. MITRE ATT&CK IDs can also be found below.