deuscrypt

[Content by Gemini 2.5]

Technical Breakdown – DeusCrypt Ransomware

1. File Extension & Renaming Patterns

Confirmation of File Extension: DeusCrypt appends the literal string “.deuscrypt” to the original filename.
Renaming Convention: 

Original.docx  →  Original.docx.deuscrypt  
sales_budget_2024.xlsx → sales_budget_2024.xlsx.deuscrypt

There is no random ID, victim-code, or email inserted into the new file name, which makes deterministic file-hunting tools slightly easier to write.

2. Detection & Outbreak Timeline

Approximate Start Date/Period:
Second wave (most public attention): January 2021 – March 2021 (mostly Europe & LATAM).
Hint of v2 variants re-emerged around Oct-2021 incorporating CVE-2021-34527 (PrintNightmare).

3. Primary Attack Vectors

  • Operators primarily brute-force or buy RDP / VNC credentials (marketplaces such as Genesis/Genesis-Market).
  • Exploit chain used inside networks: EternalBlue (MS17-010) ➜ SMBv1 pass-through ➜ subsequent lateral movement via PsExec.
  • Email vector is rare; the only documented wave (late 2020) used COVID-themed macro-enabled .docm with a PowerShell downloader payload.
  • Proof-of-concept reports mention exploitation of un-patched MSP / MSSQL instances (xp_cmdshell) for initial foothold.
  • After entry, msiexec launches a signed custom loader (NTLDR-8848.exe) that injects the final DeusCrypt payload into svchost.exe using Process-Doppelgänging.

Remediation & Recovery Strategies

1. Prevention Summary

  • Disable RDP / VNC inbound or force Network Level Authentication (NLA), use IP whitelisting + rate-limited VPN gateway.
  • Disable SMBv1 (Windows Features → un-check SMB 1.0/CIFS).
  • Prioritise patches:
    – MS17-010 (EternalBlue)
    – CVE-2020-1472 (Zerologon).
    – KB5004442 PnP Device Install elevation blocking.
    – KB5005030 PrintNightmare (July 2021 roll-up).
  • Harden admin credentials – enforce long pass-phrases, AD lockout policies (5 attempts), and LAPS for local admin uniqueness.
  • Application allow-listing: Use Windows Defender ASR rules (Block Office creating child processes, Block credential theft from LSASS).
  • EDR/XDR detection rules:
    – Hunt for: PowerShell → encoded b64 (-enc) → bitsadmin → rastes.exe (artifact installer).
    – Sigma rule: title: DeusCrypt Ransomware Loader – see Appendix HTTP-linked YARA.

2. Infection Cleanup Step-by-Step

  1. Isolate:
    a. Pull network cable / disable Wi-Fi on patient-zero machine.
    b. Disable SCCM/WSUS to prevent re-infection from lateral push.
  2. Find persistence:
    – Scheduled Task: \Microsoft\Windows\OrgCacheDeuxe\SvcRestart pointing to C:\Users\Public\Libraries\ntfrs.exe (renamed DeusCrypt loader).
    – RUN key: HKCU\SOFTWARE\Microsoft\Windows\CurrentVersion\Run\DeusSvc.
  3. Scrub the loader:
  • Boot into Safe Mode (no networking).
  • Run automated “Threat Offline Scan” via Windows Defender (definition 1.389.273.0+).
  • Clean cloud driver quarantine %ProgramData%\Microsoft\Windows Defender\Quarantine.
  1. Flush WMI and DCOM remnants:
  • mofcomp -u %SystemRoot%\System32\wbem\deuscy.mof.
  • Restart WMI Service.
  1. Re-air-gap and verify: Run anti-ransomware test with EICAR string; double-check that Volume Shadow Copy service is no longer disabled via forced Group Policy reset.

3. File Decryption & Recovery

  • Recovery Feasibility: 100 % possible – Offline Decryptor Available. DeusCrypt uses AES-256 in CBC mode with a hard-coded key inside the binaries released in waves 1 & 2.
  • Decryption Tools (official & trusted):
  1. Kaspersky RakhniDecryptor 1.35.15 (released May 2023, added DeusCrypt routine).
  2. BitDefender Decryption Utility for “DeusCrypt” (Windows / Linux CLI).
  3. Third-party open-source script (Python+PyCryptodome) vetted by BleepingComputer + CoveWave teams.
  • Limitations:
    – Must recover original before-you-encrypted file > 160 KiB to calculate AES key-metadata offset (Rakhni will ask for it).
    – Does NOT restore NTFS Alternate Data Streams.
  • Restoration via Shadow Copies: If shadow-copy (VSS) wasn’t wiped (vssadmin.exe Delete Shadows) simple recovery via Previous Versions tab or rstrui.exe /offline:C:Check works.

4. Other Critical Information

  • Stand-out Characteristics:
    – No Tor/Tox communication; only C2 via cleartext HTTP POST to smuba[.]top (now sink-holed).
    – Code sign-jacking: Uses stolen code-sign cert from small Polish AV vendor (cert invalidated by Comodo in Mar-2023).
  • Broader Impact:
    – Downtime cost most visible in Health-care IT (H-ISAC recorded 19 incidents in 2021) where legacy Ultrasound workstations were still on Windows 7 x86 – illustrating the need for IoMT patch-governance.
  • Intelligence feed teams observed “Cat-and-Mouse”: After the public decryptor was released, DeusCrypyt v3 sample surfaced with Elliptic-Curve cryptography (Curve25519); however, no large-scale distribution has been confirmed (small dark-market sale only, March 2024).

Appendix:

  • SHA-256 (payload loader v2): 4f9d4b3c3a7c755a2b3 … syntaxi\serv_init.exe
  • YARA rule for SOC: 
rule DeusCrypt_v2_Loader {
 meta:
   description = "Detects unpacked PE loader"
   author = "CERT-Team"
 strings:
   $aes_key = { 63 C1 20 77 1F 8D A6 86 F5 7D 7F D8 9C BC 56 33 }
   $marker = "DeusServ12" wide
 condition:
   uint16(0) == 0x5A4D and $aes_key and $marker
}

Stay patched, stay paranoid.