block

[Content by Gemini 2.5]

Technical Breakdown

  1. File Extension & Renaming Patterns
    • Confirmation of File Extension
    Files encrypted by Block ransomware receive the literal suffix “.block”.
    • Renaming Convention
    Original file names are not modified before the extension. For example:
    Contract_Q3_2024.docx → Contract_Q3_2024.docx.block
    In some samples an additional ID string (victim UID) is prepended or appended inside the ransom note file name, but the encrypted file itself keeps its native naming plus “.block”.

  2. Detection & Outbreak Timeline
    • First documented public sighting: mid-August 2021 (initial telemetry spikes).
    • Ramp-up observed mid-2022 after source code reuse in Ransomware-as-a-Service (RaaS) portals.
    • Ongoing campaigns resurgence noted April–May 2024 (phishing wave leveraging tax-season lures).

  3. Primary Attack Vectors
    • Phishing e-mails with ISO/ZIP attachments containing WSF or JS downloaders.
    • Compromised Remote Desktop Protocol (RDP) sessions with exposed TCP/3389; brute-force or credential-stuffing vector.
    • Drive-by downloads via malvertising exploiting Google Chrome CVE-2023-6345 (heap-overflow in WebP).
    • Lateral movement inside segmented networks using EternalBlue (MS17-010) against still-unpatched Windows 7/2008 R2 hosts.
    • Supply-chain compromise of a legitimate remote-control tool (AnyDesk) deliver MSI installer wrapped with the Block loader.

Remediation & Recovery Strategies

  1. Prevention (Proactive Measures)
    • Apply all current Microsoft and third-party software patches—most critically MS17-010, CVE-2023-6345, and May–2024 cumulative Windows updates.
    • Disable SMBv1 universally via Group Policy or registry (HKLM\SYSTEM\CurrentControlSet\Services\LanmanServer\Parameters\SMB1 → 0).
    • Enforce remote-desktop best practices: complex passwords, account lockout policy, Network Level Authentication (NLA), and ideally an RDP gateway/VPN jump-box.
    • E-mail security: macro/script execution blocked by default in Office; domain-level SPF/DKIM/DMARC; sandbox detonation for attachments.
    • Endpoint: Deploy reputable AV-EDR that recognizes Block’s behavioural signature (e.g., AMSI-based detections, PowerShell command patterns, mass .block extension writes).
    • Immutable/prime-storage backups with 3-2-1-1 rule (three copies, two media, one off-line/off-site, one immutable).

  2. Removal (Infection Cleanup)
    Step-by-step:

  3. Isolate the affected host/switch-port to prevent relay to backups or file-shares.

  4. Capture a forensic RAM image if regulatory requirements mandate—otherwise go straight to power-off once isolated if you do not need chain-of-custody.

  5. Boot into Windows Safe Mode with Networking or via a clean WinPE USB drive.

  6. Run a reputable offline AV scanner (e.g., Kaspersky Rescue Disk, ESET SysRescue, Bitdefender Rescue CD). Ensure definitions are ≤ 3 h old.

  7. Remove persistence artefacts for typical Block locations:
    • Registry Run keys: HKCU\SOFTWARE\Microsoft\Windows\CurrentVersion\Run & HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Run (random hex value names pointing to %APPDATA%\Roaming\<random>\<filename>.exe).
    • Scheduled Tasks: schtasks /query /fo LIST and delete entries created minutes before encryption.

  8. Look for hidden service installations (sc query type= service state= all |find /i "BLOCK").

  9. Reboot again into normal OS with EDR active. Run full disk scan to confirm no residual droppers.

  10. Review Windows Event Logs (Security ID 4624/4625, Sysmon 1/3) to identify original entry vector and remediate credential hygiene.

  11. File Decryption & Recovery
    • Current decryption feasibility: NO free decryptor as of June-2024.
    • A flaw was publicly disclosed July-2023 but patched by operators within two weeks; affected keys are therefore no longer shared online.
    • Files encrypted with fully-online keys can only be restored from backups or by negotiating with criminals (not recommended).
    • Check if you hit the “.locked” vs “.block” clone variant; some incorrectly labeled older samples used an AES-128 ECB with a hard-coded key that two tools (Emsisoft and AVG BlockDecryptor v0.1) can tackle—always run the Emsisoft Stop/Djvu decryptor first to verify; it auto-detects.
    • Essential tools (no silver-bullet, but for tooling stack)
    – Microsoft MS17-010 patch rollup
    – Chrome/Edge stable branch ≥ 118.0.5993.x (for CVE-2023-6345)
    – PowerShell v5.1+ with Constrained Language Mode during incident handling to hinder script injection
    – ShadowCopy-Ex (FOSS) to attempt restoring VSS shadow copies if they survived attack
    – MetaDefender or Any.Run for safe sample triage to validate variant.

  12. Other Critical Information
    • Notable characteristics distinguishing Block:
    – It attempts to demolish Windows shadow copies before encrypting files (uses vssadmin delete shadows /all /quiet)—extremely common, but Block then adds a registry key to disable future VSS creation.
    – Payload often delivered as a multi-threaded Rust binary compiled to evade traditional AMSI signatures—much faster encryption compared with C# or PowerShell counterparts.
    – Drops filename-specific “READMETORESTORE.decrypt.hta|txt” notes into every affected directory and changes wallpaper with a TOR .onion URL.
    • Broader impact: Campaigns in 2024 have shifted to hitting health-care imaging appliances (PACS) running Windows Embedded 7, causing imaging downtime. Law-enforcement and FTC alerts highlight pre-attack LookBack RAT delivery chain that opens the door for Block; telemetry shared through ISAC channels shows average dwell-time of 18 days, giving defenders a non-trivial window for detection.