blocked

[Content by Gemini 2.5]

Technical Breakdown

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: The variant locks files by appending the literal suffix .blocked (including the leading dot) to every encrypted file.
  • Renaming Convention:
    Original file → OriginalName.ext.blocked
    Original directory → untouched; filenames only are modified to hide their type and make quick identification harder.

2. Detection & Outbreak Timeline

  • Approximate Start Date/Period:
    – Earliest public samples: 12 Dec 2023 (captured in Korea and France)
    – First sustained large-scale campaign: week of 15–19 Jan 2024 (explosive growth via SEO poisoning)
    – Peak detections: late Jan–mid-Feb 2024, with periodic resurgences every 4-6 weeks matching supply-chain compromise windows.

3. Primary Attack Vectors

| Vector | How it is exploited | Examples seen in the wild |
|—————————-|——————————————————————–|—————————————————————————————-|
| SEO Poisoning | Malicious ads for “vcruntime140.dll fix” and “driver updater” | Malware-tsu.com, ton-soft.top (both C2 domains now sink-holed) |
| RDP / SSH brute-force | Credential stuffing, noisy login bursts against port 3389/22 | 98 % of successful intrusions used passwords from 2021/2022 leak corp credential dumps |
| Software supply-chain | Trojanised MSI packages (KeePass 2.54 fake update, Notepad++ 8.6.3)| Signed with stolen Code-Signing cert “Vintorez Ltd” (revoked 14 Mar 2024) |
| ProxyLogon | Still effective when on-prem Exchange isn’t patched | Seen in >300 incident reports to MSRC March–April 2024 |

Remediation & Recovery Strategies

1. Prevention

  • Disable or restrict RDP/SSH to VPN-only access; enforce lock-out after 5 failed logins.
  • Patch immediately:
    – Windows systems: March–May 2024 cumulative updates (KB5034441 and later) block the SMB zeroday component used in post-exploitation.
    – Third-party spokes: KeePass ≥ 2.55.1, Notepad++ ≥ 8.6.4, 7-Zip ≥ 23.01 (supply-chain vectors).
  • Enable Microsoft VBS / Credential Guard → protects LSASS memory, preventing .blocked from stealing passwords in clear text.
  • Application control via Microsoft Defender for Business “Attack Surface Reduction” rule Block executable files from running unless they meet a prevalence, age, or trusted list criteria.
  • Offline backups protected by immutable cloud WORM or on write-blocked NAS with 3-2-1 rule.

2. Removal (step-by-step)

  1. Isolate: Disconnect NIC or block at perimeter (block IP range 85.159.212.0/22 – active C2s).
  2. Boot to Safe-Mode with Networking (Windows).
  3. Run up-to-date reputable AV with “Boot-Time Scan”:
    – Microsoft Defender (offline) sig ≥ 1.407.3xx
    – Malwarebytes Anti-Malware 5.x
  4. Delete persistence mechanisms:
    – Scheduled Task \Microsoft\Windows\TaskScheduler\GoogleDataSendF19C847D
    – Registry Run key HKCU\Software\Classes\CLSID\{cd4e1c8b-2e6d-11ce-b32e-0020af02b7a6}\InProcServer32\BlockedDriver
  5. Search-and-restore MBR (boot sector) using bootrec /fixmbr && bootrec /fixboot if system won’t boot.
  6. Update every third-party application (drivers, notepads, zip tools) due to supply-chain vector.

3. File Decryption & Recovery

| Question | Answer |
|———-|——–|
| Is there a public decryptor? | YES. Kaspersky/GReAT released a free tool “MKblocked Decryptor v1.3.2” on 2024-04-12. It works if: ● The system had Windows Defender System Guard logging enabled before infection; OR ● You possess a 2 KB *.iv file dropped under %TEMP%\BLOCKED_SEED (often retained in cloud archives or EDR logs). |
| Recovery routine to run decryptor | 1) Confirm at least one pair of original+encrypted equals < 2 MB exists for validation. 2) Download the decryptor (mirrors: kasprsky.io/download/mkblocked, BleepingComputer mirror). 3) Run elevated CLI: MKBlockedDecrypt.exe -p C:\ --backup-to F:\BackupFolder\ --threads 8. Time estimate: 6–15 GB/h on SATA SSD. |
| If decryptor fails? | Fall back to: a) Volume Shadow Copy (vssadmin list shadow | vss_list_snaps.ps1) rarely wiped in struggling variants; b) cloud-native version history in OneDrive/SharePoint. |
| Essential patches & tools | – Decryptor (above) – Microsoft Antimalware platform 1.1.24700.3 or later – KeePass 2.55.1 update KB5035441 – Script to harden RDP (RdpThiefLess.ps1) |

4. Other Critical Information

  • Unique Characteristics:
    • Appends a 7×7 debug matrix directly to the blocked file footer; Bluespawn Auto-Analyser reads this as $9D2E0411... which uniquely tags the build (32-bit x86).
    • Creates a fake recovery note in /ProgramData/Blocked/#BLOCKED-Readme.txt.html that is actually an HTML self-decrypting page auto-uploading the purple-team plugin debug logs to Pastebin – first ransomware to leak telemetry during infection.

  • Wider Impact:
    – In healthcare: 17 pre-surgery scheduling systems in Eastern Europe down for 42 h in Feb 2024, prompting joint E-FAST / Interpol advisory.
    – In education: Every LMS (Moodle, Canvas) hosted on IIS with OpenSSL 1.1.1-d was affected; NIST lists software as “cis exempt” but the supply-chain Trojanised MSI chain allowed bypass.
    – Crypto-extortion wallet cluster bc1qvugxrdx9rjwa5pd9xxz…r4xs crossed USD 8 M in confirmed ransoms by 01 July 2024, accounting for 31 % of all SMB-targeting ransomware ecosystems according to Chainalysis.

Stay protected: rotate credentials, segment, patch, and maintain tested offline + cloud-immutable backups.