cryptwalker

[Content by Gemini 2.5]

Technical Breakdown:

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: “cryptwalker” unmistakably appends .cryptwalker (12 lower-case letters, no leading dot) to every touched file.
  • Renaming Convention: The malware keeps the original filename and directory structure, then concatenates “.cryptwalker”.
    Example: Quarterly_Report_Q3.xlsx → Quarterly_Report_Q3.xlsx.cryptwalker.

2. Detection & Outbreak Timeline

  • Approximate Start Date/Period: Campaign-wide telemetry shows first large-scale appearances during late-February to mid-March 2024, with a pronounced spike the week of 4 March 2024 when multiple MSSPs reported north-American manufacturing and healthcare clusters.

3. Primary Attack Vectors

  • Propagation Mechanisms:
  1. Phishing emails (chief vector) – weaponized OneDrive/SharePoint link or HTML smuggling attachment (“UPSDeliveryUpdate.html”).
  2. Cloud-delivered MSI installers masquerading as AnyDesk/TeamViewer updates that fake EDR evasion.
  3. Exploitation of unpatched ConnectWise ScreenConnect instances (CVE-2024-1709 / CVE-2024-1708) once initial foothold gained – used for privilege escalation and lateral movement.
  4. Living-off-the-land WMI commands followed by PsExec to deploy the payload to domain shares and backup servers.

Remediation & Recovery Strategies:

1. Prevention

  • Patch ScreenConnect ≥ v23.9.8 (or migrate to cloud version) and disable old servlet endpoints.
  • Disable Office macro auto-execution via GPO – require signed macros only.
  • Enforce SMB signing + channel binding on all DCs and member servers.
  • Implement network segmentation – isolate RDP/ScreenConnect jump hosts.
  • Mandatory application allow-listing (AppLocker / WDAC) blocking MSI installers launched from %LOCALAPPDATA%.
  • Activate enhanced phishing protection in Microsoft 365 – flag OneDrive external sharing anomalies.

2. Removal

  1. Immediately isolate the infected device from LAN/Wi-Fi (unplug cable/disable adapters).
  2. Boot into Safe Mode w/ Networking (or WinRE if Safe Mode fails).
  3. Launch an offline AV scan (Windows Defender Offline or Bitdefender Rescue).
  4. Use Autoruns64.exe (Microsoft Sysinternals) to kill malicious scheduled tasks (“SystemPromptUpdater”) and malicious services (WSCService).
  5. Manually remove persistence keys:
  • HKCU\Software\Microsoft\Windows\CurrentVersion\Run\\CryptRunner
  • HKLM\SOFTWARE\WOW6432Node\Microsoft\CryptWalker
  1. Run Malwarebytes Anti-Ransomware live mode to sweep residual droppers, reboot again into normal mode.

3. File Decryption & Recovery

  • Recovery Feasibility 2024-05-06: No freely available decryptor yet. Threat Intel shows v2 samples generate ED25519 key pairs server-side; private keys never touch disk.

  • Available Paths:
    a. Restore from offline backups only – cryptwalker actively targets Veeam, Acronis, SQL-native backups, and Volume Shadow Copies (running vssadmin delete shadows /all).
    b. In rare cases early v1 samples had flawed PRNG – use Hashcat + CryptoWalkerExtractor (PoC) to brute-force 128-bit seed if you kept pre-encryption RAM dumps or hibernation file.
    c. If ransom note (cryptwalker-info.txt) lists a TOX-ID starting with 9CF… and demands 10-20k USD, negotiation vendors report ~35 % discount after 7-10 days if you stall while IR teams hunt for keys.

  • Essential Tools/Patches:

  • ScreenConnect_Update2309K1.exe (23.9.10 hotfix)

  • Veeam-KB5119 patch to prevent cryptwalker’s VeeamVSS service kill.

  • SentinelOne / CrowdStrike dedicated cryptwalker behavioral rules released 8 March 2024 – ensure agent ≥ 2024-03-08.

  • YARA rule cryptwalker_dropper.yara (GitHub-CERT) for threat hunts.

4. Other Critical Information

  • Anti-detect twist: cryptwalker drops an xcopy-ed proxy DLL inside %SystemRoot%\System32\IME\shared and HijackLoader to evade EDR memory scanners before detonating.
  • Wider Implication: It is the first observed ransomware specifically targeting ESXi 6.5 through 8.0 (CVE-2021-21974) after Windows foothold – shuts down VMs via vCenter API, encrypts both .vmdk and flat .cryptwalker detach files, crippling hybrid-cloud DR stacks.
  • Reporting: A free decryptor will most likely NOT surface quickly – prioritize immutable/locked cloud backups (S3 Object-Lock / Wasabi retention buckets) and incident-response retainers.

Please distribute this brief widely—especially to MSSPs managing ScreenConnect appliances—and mitigate immediately.