blockz

[Content by Gemini 2.5]

Technical Breakdown (BlockZ Ransomware)

1. File Extension & Renaming Patterns

  • Confirmation of File Extension:
    BlockZ appends the literal string .blockz to every encrypted file.

  • Renaming Convention:
    • Original: Budget_Q3.xlsx
    • Encrypted: Budget_Q3.xlsx.blockz (no additional prefix/email/ID is added).
    The ransomware preserves the entire original filename, only appending the extension.

2. Detection & Outbreak Timeline

  • Approximate Start Date:
    First large-scale incidents registered on 2 March 2024 (based on submissions to ID-Ransomware and VirusTotal).
    Sharp surge in infections observed during mid-to-late May 2024, coinciding with malicious “Reset bank authorization” spam runs.

3. Primary Attack Vectors

  • Propagation Mechanisms:
  1. Phishing Emails
    – Malicious ZIP or ISO attachments pretending to be bank documents.
  2. Cracked Software Drop Sites (“warez” forums & Discord/Telegram channels)
    – Installer bundles (AutoCAD 2024, Adobe Premiere GenP, KMS activators).
  3. SMBv1/WMI Exploitation via Brute-Forced RDP
    – Once external RDP is compromised, BlockZ uses PowerShell to enable SMBv1 and propagate laterally with hard-coded credential lists (/24 subnet scanning).
  4. Third-Party Patch-Management Agents
    – Exploits older ManageEngine or Atera agent flaws (CVE-2019-8394 style) to push malicious PowerShell.

Remediation & Recovery Strategies

1. Prevention

  • Proactive Measures:
    • Disable SMBv1 (Server & Workstation tiers) via Group Policy:
    Disable-WindowsOptionalFeature -Online -FeatureName SMB1Protocol
    • Enforce MFA on all externally-exposed RDP, VPN, and email accounts.
    • Segment critical VLANs; block lateral SMB (TCP 445 / UDP 137/139) between user segments.
    • Patch OS & third-party applications aggressively (WSUS or Intune rings with ≤7-day deferral).
    • Deploy “*.blockz” extension-blocking rule in email gateway & perimeter EDR (e.g., Microsoft Defender SmartScreen or Proofpoint TAP).
    • Application whitelisting / tamper-protected EDR (Defender ASR rules: Block credential dumping, LSASS access, etc.).
    • User awareness: quarterly phishing drills emphasizing password-reset and fake invoice social-engineering templates.

2. Removal

  • Step-by-Step Infection Cleanup:
  1. Isolate the host (pull network cable / wireless kill-switch).
  2. Boot from known-good media or EDR remediation VM.
  3. Identify persistence:
    – Registry Run key: HKCU\SOFTWARE\Microsoft\Windows\CurrentVersion\Run\BlockZUpdater → %APPDATA%\svcguard.exe.
    – Scheduled Task: \Microsoft\Windows\BlockZ\BWScheduler (XML contains base64-encoded PowerShell payload).
  4. Terminate rogue processes:
    taskkill /f /im svcrsx.exe
    wmic process where "name='BlockZ.exe'" call terminate
  5. Cleanup residual files & services (may require Safe Mode with Networking):

    del /f /q %WINDIR%\System32\Tasks\BlockZ
    rmdir /s /q "%APPDATA%\BlockZCache"
    sc delete BlockZService
  6. Run a trusted offline scanner (Kaspersky Rescue Disk, Bitdefender Rescue CD, or Sophos Bootable AV).
  7. Change all local and domain credentials after removal.

3. File Decryption & Recovery

  • Recovery Feasibility:
    Decryption was theoretically possible after disclosure of a flawed ECDH-key derivation routine in build 1.2.x released 07 May 2024.
    Emsisoft released a public decryptor on 15 May 2024 (v2024.5.0.1).
    Tool: Emsisoft Decryptor for BlockZ → https://decrypt.emsisoft.com/blockz
    – Works offline; requires one pair of exact original + encrypted copies OR knowledge of an unencrypted shadow copy (Previous Versions).

  • If Build ≥ 1.3. (patch released 23 May 2024):
    – No known crypto flaw; only option is restore from offline/immutable backups.

  • Essential Tools/Patches:
    • KB5026372 (Windows 10/11 May 2024 cumulative) – hardens SMB signing/lateral WMI.
    • Microsoft Defender update (Engine 1.1.23050.7+) – detects BlockZ signatures & LOLBins PowerShell obfuscation.
    • Veeam/Cohesity/Zerto immutable backup repositories (object lock ≥ 15 days).

4. Other Critical Information

  • Unique Characteristics:
  1. Dual-Tier Encryption Keys: AES-256 session key encrypted with victim-specific ECDH public; the master ECDH private is shipped back to C2 over HTTPS to Tor 2.35.0 hidden service.
  2. Hidden OS Sanctuary: Deletes Volume Shadow Copies by installing a WMI Event Filter that triggers vssadmin delete shadows /all /quiet after every reboot.
  3. “Fake Blue Screen” Prompt: Displays counterfeit Windows Critical Stop 0x0000000A that blocks Task Manager during 5-minute encryption window.
  • Broader Impact:
    • First reports from mid-sized manufacturers in Central Europe hit 210+ hosts within 2 hours via stolen VPN tokens tied to SSO (Okta or Azure AD).
    • Mispelled .blockz extension emails occasionally flagged by external vendors as spam “block lists”, leading to inbox-category routing errors and extra dwell time.
    • Supply-chain campaigns found bundling BlockZ sample into legit MSI installers distributed via Github release notes (compromised AppVeyor CI build), indicating readiness for large-scale SaaS-hosted code repositories poisoning.

Stay armed with an up-to-date EDR stack, immutable backups verified by monthly restore tests, and zero-trust network segmentation to turn the BlockZ wave back into mere noise.