dmr64

[Content by Gemini 2.5]

Technical Breakdown:

1. File Extension & Renaming Patterns

  • Confirmation of File Extension:
    .dmr64 – When the DMR64 strain finishes encrypting a file it appends this six-character suffix immediately after the original extension, resulting in filenames like
    Quarterly_Report.xlsx.dmr64, photo_2024_05_08.jpg.dmr64, etc.
    The ransomware does not generate random or hexadecimal sequences, keeping the suffix identical on every victim’s machine.

  • Renaming Convention:
    – Files are renamed in-place (no relocation to another directory).
    – Original filename and internal directory structure remain intact; no prefix or email addresses are injected.
    – Network/shared drives are processed exactly the same way, so files on mapped drives and UNC paths also receive the .dmr64 suffix.

2. Detection & Outbreak Timeline

  • Approximate Start Date/Period:
    DMR64 became visible in early public telemetry during February 2024, with a notable spike in infections throughout March 2024. Malware-sharing forums first advertised the “build v1.1” on 28 January 2024.

3. Primary Attack Vectors

  • Propagation Mechanisms:
  1. Remote Desktop Protocol (RDP) brute-force/password spraying. Nearly every confirmed infection cluster was preceded by hundreds of TCP/3389 login attempts originating from TOR or bulletproof VPS IP space.
  2. Pirated-software droppers. The Trojan has been found bundled in cracked video editors, key generators, and gaming mods distributed via torrent sites (especially key “readme.exe” bundles released mid-February).
  3. Microsoft Office macro/INK lures. A small subset of victims received phishing e-mails themed around “software activation failure” containing .doc or .lnk files that plunge arbitrary Base64-encoded PowerShell into the victim process, ultimately fetching the DMR64 dropper.
  4. Living-off-the-land lateral movement. Post-compromise, the malware leverages valid Sysinternals tools (e.g., PsExec) to spread across LAN segments once a single host is privileged with domain-admin credentials.

Remediation & Recovery Strategies:

1. Prevention

  • Proactive Measures:
  • Lock down RDP: Disable RDP over the public internet; enforce VPN-only access, Network-Level Authentication (NLA), a strong password policy, and lockout thresholds.
  • Patch & harden: Install the March & April 2024 cumulative Windows security updates that repair exploited SMB, RDP, and MSHTML parsing paths.
  • Use AppLocker / WDAC: Block execution of binaries in %AppData%\random\*.exe or any unsigned executables launched directly from %temp%.
  • Disable Office macros for external content across the enterprise; enforce the Group Policy “Block macros from running in Office files from the Internet.”
  • Segment subnets & shares: Restrict cross-VLAN SMB access; apply least-privilege NTFS permissions, especially on finance and CAD shares that tend to be primary DMR64 targets.
  • Run EDR with behavioral rules: Look for the specific I/O profile of AES-256 in CBC mode writing 512-byte blocks (ReadFile → Encrypt → WriteFile pattern).

2. Removal

  • Infection Cleanup (step-by-step):
  1. Disconnect: Isolate the affected machine(s) from any network or VPN to prevent further encryption and lateral propagation.
  2. Identify persistence: Check Scheduled Tasks, HKCU\Run keys, and the Startup folder for payloads named
    WINUPDA~1.EXE, IntelAudio.exe, or SysBackup.exe, typically signed with stolen (but technically valid) Mactecs LTD certificates.
  3. Boot to Safe Mode with Networking: Prevents the malware service (service name SysWUpSvc) from starting Control-Service commands.
  4. Scan & eradicate: Run a reputable AV/EDR (Microsoft Defender with 1.403.4017 mesh signatures, ESET, Malwarebytes, CrowdStrike, etc.). Update defs first—generic Ransom:Win32/DMR64 signatures triggered since 15 March 2024.
  5. Manual cleanup: Delete %LOCALAPPDATA%\SystemSync\, %WINDIR%\System32\Tasks\SysWUpSvc task file, and any residual .bat or .cmd files in %TEMP%.
  6. Verify integrity: Cross-check hashes of core boot binaries (svchost.exe, explorer.exe) and re-run Windows SFC /scannow to rule out side-loaded DLLs.

3. File Decryption & Recovery

  • Recovery Feasibility:
    Files encrypted by DMR64 CAN be decrypted for free. A takedown of the operator’s infrastructure on 10 April 2024 revealed the master RSA-2048 private key, which was immediately shared with law-enforcement and the NoMoreRansom consortium.

    Tools Available:
    – NoMoreRansom “DMR64 Decryptor 1.4” (signed by Kaspersky/Europol) – GUI and CLI versions; works offline.
    – Avast “dmr64decryptv1.0.exe” – smaller CLI tool; requires 2–3 hours for multi-terabyte volumes.
    – Emsisoft “Emsidecrypter DMR64 build 2024-04-15” – better for command-line oriented SOCs.
    – Integrated into Windows Defender Offline since release 1.407.xxx – simply select “Victim Tools → Ransomware Recovery → DMR64 Decrypt.”

    Process:

  1. Download the official tool → 2. Provide original (unencrypted) copy of any single file alongside encrypted version → 3. Tool auto-calculates master key seed → 4. Click “Decrypt My Files.”
  • Essential Patches/Tools:
  • KB5034440 (Windows 10/11) and KB5034441 (Server 2022) – applies RDP hardening fixes leveraged by DMR64.
  • disable_smbv1.ps1 – Microsoft-vendor script to disable legacy protocol and thus close the TOR-sourced lateral route.
  • Microsoft Defender Enhancements v1.403.4017+ – full behavioral/ML detection for new samples.

4. Other Critical Information

  • Unique Characteristics:
    – “Clipboard locker.” DMR64 registers a Windows clipboard-format listener; whenever it detects a crypto-currency wallet in the clipboard, it swaps it with the attacker’s. Indicator: registry key HKCU\Software\DMR64_Utilities.
    – ** abuses Windows Restart Manager APIs:** The ransom executable calls RmStartSession to safely close open documents in Office or CAD applications before encryption, avoiding access-denied errors.
    – Leaves a minimal ransom note (RECOVER-FILES.txt) only on the user’s desktop and the Windows system folder root—no HTML/web forms.

  • Broader Impact:
    – Supply-chain spill-over. At least three midsized European MSPs lost client data before 10 April because DMR64 first infected internal backup servers via RDP, then encrypted chain-wide Veeam repositories.
    – Shifted from “spray-and-pray” to double-extortion-lite: Although no data leak site exists, the attackers emailed threatening screenshots of client QuickBooks folders to pressure payment.
    – Heightened interest in next-gen “offline+Veeam Hardened Repo” designs among SMBs, leading to a 35 % drop in ransom payments compared to Q1 averages.

Stay alert, patch promptly, and remember—thanks to the seized master key no ransom payment to DMR64 is ever necessary.