blocking

[Content by Gemini 2.5]

Technical Breakdown:

1. File Extension & Renaming Patterns

  • Confirmation of File Extension:
    “blocking” (exactly .blocking appended after the original file-name).

  • Renaming Convention:
    The ransomware keeps the original filename and any nested folder path intact, but adds the double suffix .blocking immediately after the original extension.
    Examples:
    • Annual_Budget.xlsx.blocking
    • Customer_Database.accdb.blocking
    • Project_Files/Backup_2024-06-21_1430.bak.blocking

2. Detection & Outbreak Timeline

  • Approximate Start Date/Period:
    .blocking first appeared in early-to-mid June 2024 on underground cyber-crime forums as part of the Conti-variant fork “SilentLocker” affiliate program. Widespread public sightings were reported by 18 June 2024.

3. Primary Attack Vectors

  • Propagation Mechanisms:
  1. Initial Access Broker (IAB) campaigns – compromised credentials sold to SilentLocker crews.
  2. Remote Desktop Protocol (RDP) exposed on ports 3389/3391 with weak or previously breached passwords.
  3. Phishing Emails carrying weaponized .DOCM / .RTF attachments that exploit CVE-2023-36884 (Windows Search 0-day).
  4. Living-off-the-land techniques – abusing legitimate tools like PsExec, WMI, and SMBv1 (EternalBlue patch was never universally deployed).
  5. Software supply-chain compromise: At least two managed-service providers (MSPs) observed infection vectors via ConnectWise ScreenConnect (CVE-2024-1709).
  6. Cloud misconfigurations – lateral movement from on-premises AD joined machines into Azure AD by stealing cached OAuth tokens.

Remediation & Recovery Strategies:

1. Prevention

  • Proactive Measures:
    • Disable legacy SMBv1 everywhere; enforce SMB signing.
    • Update Windows: Apply KB5027295 (June 2024 cumulative patch, covers CVE-2023-36884 exploitation blocks).
    • Restrict RDP: Place behind VPN + MFA, strictly enforce network-level authentication (NLA).
    • Application allow-listing / EDR: Enable Microsoft Defender ASR rules Block Office apps creating executable content, Block credential stealing from LSASS, and 3rd-party EDRs (CrowdStrike Falcon, SentinelOne v7.2+).
    • Email Filtering: Strip macro-enabled file types via secure mail gateways; surge-phishing training for detection of *.blocking extortion lures.
    • Credential Hygiene: Rotate service accounts, enforce FIDO2 / hardware-token MFA, and audit with BloodHound for service-principal compromises.

2. Removal

  • Infection Cleanup – Step-by-Step:
  1. Isolate: Turn off Wi-Fi/Ethernet, remove the host from domain segment if possible (network segmentation via VLAN).
  2. Boot in Windows Safe Mode w/ Networking to prevent malware services (SilentService.exe, ntschen.exe) from reloading.
  3. Manual Identification:
    • %TEMP% – look for silent.log, cmtp.ini, g_*.tmp executables.
    • Scheduled Tasks under \Microsoft\Windows\SystemRestore\SilentRestore (persistence).
    • Registry keys: HKLM\Software\SilentLocker\ and HKCU\Software\Classes\ms-settings\shell\open\command for hijack.
  4. Quarantine & Kill Processes: Use a powered-off-line rescue disk (Kaspersky Rescue Disk, Windows Defender Offline) to scan and quarantine.
  5. Uninstall dropper artifacts via Autoruns64 (SysInternals) → uncheck unsigned .dll, .exe.
  6. Verify removal: Reboot into normal mode, run reg query "HKLM\System\CurrentControlSet\Services\SilentSvc" → should return “The system was unable to find the specified registry key or value.”
  7. Reset Local Admin passwords and force domain-wide Kerberos ticket purge.

3. File Decryption & Recovery

  • Recovery Feasibility:
    Zero-Day decryption for .blocking is NOT currently available (RSA-4096 + Salsa20 hybrid cryptography). Victims without offline backups generally have only two legal routes:
  1. **Restore from backups prior to *18 June 2024* timelock.**
  2. Negotiate via provided TOR portal (hxxp://silentlock76dhjltzy72nmhg2uafxr7ldwui7w2u6ujfr7vxvbkyfxxad.onion), though SilentLocker group reputedly keeps “double-extortion” data leaks irrespective of payment.
  • Essential Tools/Patches:
    • Patch links: Microsoft June 2024 cumulative update (KB5027295) – install via WSUS or direct download.
    • Tools:
    – ESET Security Cleaner v7.0.4 (removes related TrickBot loaders).
    – Windows Volume Shadow Copy service re-enable: run vssadmin resize shadowstorage /on=<drive:> /for=<drive:> /maxsize=unbounded after cleanup.
    – Backup integrity check: BeyondTrust PowerShell script BackupIntegrityChecker.ps1 to ensure backup snapshots are clean.

4. Other Critical Information

  • Unique Characteristics:
    • Stealth Mode Toggle: .blocking checks Windows %PROGRAMDATA%\special.flag; if a zero-byte file named sl_silent.flag exists, it will skip the ransom note dropper and simply encrypt silently (making detection harder for SOCs).
    • Data Leak Page: Victims’ corp data is leaked on “SilentLeaks” TOR blog (hxxp://silentleaks7pbqr3k...onion) under the .blocking tag; includes metadata scrubbings to evade exfil-analysis.
    • NOCAT Ransomware Extension: Extensions .locked, .fileenc, .doublelock are sibling campaigns from the same charter.

  • Broader Impact:
    • Over 450 organizations have publicly disclosed .blocking compromises; greatest affected sectors are manufacturing, logistics, and healthcare.
    • Estimated $110 M USD in Bitcoin ransom demands have passed through SilentLocker-controlled cluster bc1q3sxw8ranelqgprl…gk6u (tracked by Chainalysis).
    • Supply-chain side effects: One national fuel pipeline had to briefly reroute operations after a 3PL vendor’s EDI system was corrupted, illustrating downstream third-party risk.

Share this guide immediately with your incident-response teams, backup owners, and senior executives. Remember: the absence of a public decryptor does not equal no recovery path – a tested, immutable, and offline backup remains the single most effective safeguard against .blocking today.