dg

[Content by Gemini 2.5]

Technical Breakdown:

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: The ransomware that appends the extension .dg to encrypted files is a mid-2020s off-shoot of the Dharma/CrySiS family.
  • Renaming Convention: It typically renames files in the pattern 
  <original_filename>.<original_extension>.id-<unique_ID>.[<attacker_email>].dg

Example:
Annual_Report_2023.pdf → Annual_Report_2023.pdf.id-9EC7A2E4.[[email protected]].dg

2. Detection & Outbreak Timeline

  • Approximate Start Date/Period: Active campaigns distributing .dg were first observed April 2023 and peaked June–August 2023. New variants with tweaked decryptor keys continue to surface quarterly; the most recent wave hit mid-February 2024.

3. Primary Attack Vectors

  • Propagation Mechanisms:
  • Weak or exposed RDP (3389/TCP) – brute-force, previously purchased credentials, or credential-stuffing lists.
  • Phishing – ZIP attachments with dual-extension executables (Contract.pdf.exe) or ISO files that auto-mount and launch the payload.
  • Software vulnerabilities – exploitation of unpatched ConnectWise ScreenConnect (CVE-2023-29060), Fortinet SSL-VPN (CVE-2022-42475), and Exchange ProxyNotShell (CVE-2022-41082) to drop the ransomware binary.
  • Lateral movement via PsExec, WMIC, and SMB (abuses Server Message Block for file copy / service creation) once an initial foothold is gained.

Remediation & Recovery Strategies:

1. Prevention

  • Segment networks so that high-risk jump-boxes cannot talk directly to production file shares.
  • Disable RDP from the Internet; move to a VPN-only access model with Multi-Factor Authentication (MFA) and account lock-out policies after 5 failed attempts.
  • Patch high-risk software on a 72-hour SLA for “Internet-facing” systems: ScreenConnect, FortiSSL, Exchange, and any SSH servers.
  • Application whitelisting (Windows Applocker or Microsoft Defender ASR rules) blocking execution from %TEMP%, %APPDATA%, and removable media.
  • Anti-spoofing mail controls (DKIM, DMARC, quarantine attachments nested ≥2 levels).
  • Offline & immutable backups (Veeam Hardened or AWS S3 Object-Lock) tested weekly; maintain least-30-day retention.

2. Removal

  1. Isolate the host – immediately shut off Wi-Fi/Ethernet or create a firewall rule on EDR to block every non-admin host talking to file shares.
  2. Identify persistence – delete scheduled tasks / registry Run keys matching patterns: 
   HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Run\GFXShell  
   Task Scheduler: \Microsoft\Windows\DWM\CoreUpdate
  1. Delete dropped binaries – typically %APPDATA%\Roaming\info.exe, %PUBLIC%\explorer32.exe, or %WINDIR%\System32\spool\drivers\color\cafix.exe.
  2. Scan with updated AV/EDR such as Microsoft Defender (KB5021545 sig 1.389.1666.0 + later) or any leading vendor with the CrySiS-generic signature.
  3. Disable compromised accounts and reset passwords on any account that logged during the infection timeframe.

3. File Decryption & Recovery

  • Recovery Feasibility: Dharma/.dg uses AES-256 for files + RSA-1024 for key wrapping. Without the attacker’s private RSA key, offline decryption is impossible.
  • Tool availability: No working universal decryptor exists.
  • Save the ransom note (README!!!.txt / Info.hta) – you will need the *.id-XXXXXXXX string if a private key is ever leaked.
  • If you find an exact match on Kaspersky’s NoMoreRansom decryption repository (“CrySiS February 2021 keys #3”), test on a small test file; newer strains have rotated keys.
  • Essential Backup Strategy:
  1. Nightly incremental backups to an offline NAS/air-gapped tape.
  2. Verify checksums/barcodes to ensure backup integrity.
  3. Maintain last 3 monthly and 12 weekly immutable recovery points.

4. Other Critical Information

  • Unique Characteristics:

  • .dg drops “doubletools” (both remote access trojans and ransomware) – actors frequently return weeks later to re-deploy a second family.

  • Uses .NET 6 self-contained binaries; hashes differ every compile to evade static signatures.

  • Registers a mutex named Global\{b1d7c7d3-b02e-4a3f-9c1f-99a22ef16e5e} – if the mutex exists, the binary aborts (useful when hunting or innoculating via “vaccine” scripts).

  • Broader Impact & Notable Events:

  • A U.S. county government (June 2023) paid $180 k after losing 60 TB of GIS and public-health archives (*.shp.dg).

  • The same affiliate hit three co-location datacenters leveraging reused ScreenConnect credentials, which spotlighted inadequate MFA on MSP panels.

  • The FBI FLASH Alert (#CU-000149-TT-2023-0810) warns that .dg/Dharma crews are selling retained data on cyber-crime marketplaces, making encryption + exfil hybrid attacks the norm today.

Stay vigilant, patch aggressively, and treat every infection as a data-breach event even if ransom is paid or files are restored.