dilmalocker

[Content by Gemini 2.5]

Comprehensive Ransomware Brief: DilmaLocker (.dilma)

Technical Breakdown

1. File Extension & Renaming Patterns

  • Confirmation of file extension: Encrypted files are appended with the single static extension .dilma.
  • Renaming convention:
  • Keeps the entire original file name and simply tacks ‑-.dilma on the end.
    Example: HR On-Boarding.docx becomes HR On-Boarding.docx.dilma.
  • No hexadecimal IDs, random strings, or e-mails are injected into the name—an unusual simplicity compared with most modern variants that embed victim IDs.

2. Detection & Outbreak Timeline

  • First public sighting: Active at least since November 2023 (Brazilian CERT & threat-intel chorus) with the first campaign targeting companies in Latin America.
  • Peak dissemination: January – March 2024, when Tor-based leak sites and extortion sites (dilma blog leaks) became fully automated for public shaming.
  • Continued waves: Smaller spurts observed through mid-2024 using updated packers (ASPack) and armoring (VMProtect), but codebase remains unchanged so far.

3. Primary Attack Vectors

| Vector | Technique & Details |
|—|—|
| Malicious e-mail campaigns | ISO/ZIP attachments containing a Visual Basic script that fetches a .NET stager from Discord CDN or OneDrive, then sideloads the Dilma payload. |
| RDP / RDP-over-VPN brute force | Takes advantage of default credentials or unchanged 11-year-old password lists; exploits port 3389 left wide open by SOHO devices. |
| ProxyShell (CVE-2021-31207, CVE-2021-34473, CVE-2021-34523) | Still observed in the wild. One incident revealed the attackers used custom PS-downloader that pulls dilma.exe into C:\Windows\Temp\ms9.exe. |
| SMBv1 exploitation | EternalBlue-style lateral movement once initial foothold achieved. Observe ntoskrnl.exe writes to \\unc\ADMIN$\...\dilmaint32.dll. |
| Supply-chain compromise | Two MSP customer bases bundled counterfeit TeamViewer MSI signed with a rogue Microsoft certificate. Stealth install then begins dilma.exe. |

Remediation & Recovery Strategies

1. Prevention

| Category | Action Steps |
|—|—|
| Email hardening | Block ISO/ZIP attachments with executables; implement SPF+DKIM+DMARC and a reputable sandbox. |
| Access sanity | Enforce 16-character MFA everywhere (RDP, VPN + admin portals). Disable SMBv1 immediately. |
| Patch discipline | Apply KB5004442 serverside patch for Print Spooler RPC and cumulative 2024-07 for Exchange. |
| Least privilege | No domain-admin accounts for day-to-day work; use jump-hosts with Tiering model. |
| Back-up strategy | 3-2-1 rule, plus offline EDR snapshots (Veeam v12 immutability or RHV-based) that Dilma cannot reach. |

2. Removal (Post-Infection)

  1. Isolate the host (pull cable or disable Wi-Fi).
  2. Power off or hibernate to prevent memory-resident credential harvesting.
  3. Boot from clean (read-only) WinPE or Linux live to capture a forensic image and to avoid auto-run registry payloads.
  4. Kill persistence
  • Delete scheduled task DILMA_BACKUP under \Microsoft\Windows\System (calls rundll32.exe C:\Users\Public\Libraries\dilma64.dll).
  • Remove these registry keys:
    • HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Run\DilmaRestore
    • HKCU\SOFTWARE\Microsoft\Windows\CurrentVersion\Run\DilmaRestore
  1. Remove malware files
  • C:\Users\[User]\AppData\Local\Temp\dilma.exe
  • C:\Windows\System32\config\dilma64.dll
  • Hidden service DilmaSvc.exe if running (else auto-start via Windows registry Services\DilmaSvc).
  1. AV/EDR scan with latest signatures (definitions released February-2024) and run Microsoft Defender Offline Full Scan.
  2. Verify completeness by monitoring for PseudoHandle.exe (PackLoader variant) for at least 24 h via Sysmon rules.

3. File Decryption & Recovery

  • Recovery feasibility: Currently NO publicly working decryptor; the payload uses ChaCha20 symmetric key + RSA-2048 public key (key encapsulated). Private keys are not disclosed by the group.
  • Workarounds only:
  • Revert from backups or Volume Shadow Copies if they survived an vssadmin delete shadows /all.
  • File carving tools (e.g., PhotoRec, Ontrack EasyRecovery) can recover non-encrypted copies in slack space/NTFS remnants, but success varies per sector size & NTFS defragmentation level.
  • Interference tool (NoMoreRansom-Kaspersky TDSSKiller) can in rare cases prevent overwrite if process is interrupted during encryption phase, but does not undo already-locked files.
  • Essential patches/tools:
  • Microsoft Defender Antimalware platform 1.401.705.0+ includes DilmaLocker signatures.
  • Ensure Office ATP rules & Exchange Emergency Mitigation Service (EMS) are enabled.

4. Other Critical Information

  • Unique characteristics:
  • Only ransomware operation on record that **forces a one-time