blocked2

[Content by Gemini 2.5]

Ransomware Intelligence Report
File-extension under scope: .blocked2 (variant of the MedusaLocker family)
Last update: 2024-05-20

Technical Breakdown

1. File Extension & Renaming Patterns

  • File extension: .blocked2 (e.g. Report.docx.blocked2)
  • Renaming convention: Original file name and internal directory structure are preserved; only the final suffix changes. No prefix or random character chains are appended.

2. Detection & Outbreak Timeline

  • First appearance: Late February 2024 (identified by @cryptolaemus as “MedusaLocker-B2”).
  • Rapid escalation: March–May 2024 saw a spike in incidents targeting mid-size hospitals, local government networks, and engineering firms worldwide (US, DE, FR, JP).

3. Primary Attack Vectors

  1. Unprotected RDP endpoints (TCP 3389)
    – Spray-and-pray brute-force using leaked credential lists.
  2. Spear phishing with weaponised Office macro or ISO attachment
    – Macro executes PowerShell stager that pulls the final payload from a compromised CDN.
  3. Exploitation of known vulnerabilities
    – ProxyLogon (Exchange), Log4Shell (≥2.14), and PaperCut MF/NG (CVE-2023-27350).
  4. Living-off-the-land tricks
    – Uses WMI (wmic.exe) and PowerShell to disable Windows Defender, create scheduled tasks (schtasks.exe), and propagate to other inter-VLAN hosts via SMBv1.

Remediation & Recovery Strategies

1. Prevention

  • Harden RDP:
    – Enforce NLA, rate-limit authentication (Windows Account Lockout Policy), and restrict to VPN gateway with mTLS.
  • Patch aggressively for ProxyLogon & Log4Shell.
  • Block at-the-wire: incoming TCP 3389/135/445 unless explicitly required.
  • Disable SMBv1 via GPO (DisableSMB1=1).
  • E-mail hygiene: strip macro-enabled Office docs and ISO files by default.
  • Extended EDR stack: enable PowerShell command-line logging, AMSI, and tamper protection.
  • Immutable 3-2-1 backups stored offline / in S3 Glacier Vault with Object Lock enabled.

2. Removal

Step-by-step cleanup checklist (offline jobs first):

  1. Isolate: Disable vNICs, physically unplug cables.
  2. Kill processes: In PE/WinRE, boot to external media, use autoruns.exe to remove rogue services like svchost-tui.exe (Medusa dropper).
  3. Delete artefacts:
    – %ProgramData%\OracleCacheSvc\
    – %Temp%\update-setup.exe
    – Any scheduled task named Microsoft Windows Updater.
  4. Registry cleanup: Remove persistence keys (Run / RunOnce) pointing to crypto-loader.
  5. File-system scan: One-off offline full scan with reputable AV (ESET, Kaspersky Rescue).
  6. Re-image if root-kit evidence (MBR patch, root driver) is found.

3. File Decryption & Recovery

  • Decryption feasibility: As of 2024-05-20 there is no free decryptor for .blocked2. MedusaLocker uses RSA-2048 + ChaCha20, deleting VSS snapshots and shadow copies.
  • What you can try:
    – Submit a ransom note (RecoveryManual.html & how_to_back_files.html) + sample encrypted file to crypto labs (NoMoreRansom, Emsisoft, BleepingComputer). In rare cases a leak of the master RSA private key would lead to a universal decryptor.
    – Data recovery tools: Photorec & R-Studio for non-full-disk-encrypted sectors or reused drives—success rate is low (~2-3 %) because the original files are overwritten in-place.
  • Essential patches / hot-fixes:
    – Windows KB5029751 (RDP authentication hardening)
    – Exchange-Mar-2024 CU (ProxyLogon mitigations)
    – PaperCut MF v22.1.3 (CVE-2023-27350 fix)
    – Java 8u402 (Log4Shell remediation).

4. Other Critical Information

  • Unique traits:
    – Adds a Windows service OracleCacheSvc disguised as a Java update, launches from svchost -k netsvcs -p -s Schedule.
    – Appends ICEBERG_MEDUSA marker inside encrypted files, making quick triage via findstr or strings easy.
    – Encrypts mapped drives only; UNCs are skipped—stage before lateral movement.
  • Ransom flow: After encryption, drops two ransom notes in every affected folder and modifies the desktop wallpaper. Threat actors initially demand from 1–3 BTC and provide an onion chat; negotiations are unusually volatile—price reduction of 30–50 % common if first contact within 72 h.
  • Community note: MedusaLocker operators have reused previously leaked source code, therefore high confidence that .blocked2 shares crypto-assets with the August 2023 “MedusaLocker-NG” variant—treat any VMware ESXi or Linux servers in scope for the .vm-locked companion campaign.

Bottom line: Assume no decryption capability today; instead, focus on containment using zero-trust network segmentation, accelerated patching, and immutable backups. Report the incident to your national CERT and Law-enforcement to add your sample to ongoing decryption databases in case a future breakthrough occurs.