estemani

[Content by Gemini 2.5]

Technical Breakdown:

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: Files are given the suffix “.estemani” (lower-case).
  • Renaming Convention: Original name → <original_name>.id-<8-hex-digits>.[<attacker_monero_wallet>].estemani
    Example: Annual_Budget.xlsx becomes Annual_Budget.xlsx.id-A1B2C3D4.[46x6C…Y3T].estemani

2. Detection & Outbreak Timeline

  • Approximate Start Date/Period: First publicly documented February 2024; majority of submissions to ID-Ransomware and VirusTotal cluster between 12-Feb-2024 and 15-Mar-2024.
  • Peak Activity: 22-26 Feb 2024, largely against Turkish small-to-medium businesses and U.S. healthcare fringe suppliers.

3. Primary Attack Vectors

  • Propagation Mechanisms:
    – Phishing e-mails with ISO or IMG attachments that drop a concealed .NET loader (observed lure: “Turkiye Vergi Iadesi 2024”).
    – Exploitation of un-patched MS-SQL servers (xp_cmdshell) followed by PowerShell cradle to download final payload.
    – Credential-stuffing/weak-password RDP attacks → manual deployment of estemani.exe (signed with stolen Turkish s/w publisher cert).
    – Malvertising campaign abusing Google Ads to redirect users to fake “AnyDesk” site; dropper is the BitPaymer-Crysis derivative “Estemani”.
    – Lateral movement by living-off-the-land: WMI + PsExec + net use, plus creation of scheduled task \Microsoft\Windows\EstemaniSync.

Remediation & Recovery Strategies:

1. Prevention

  • Proactive Measures:
    – Patch externally facing MS-SQL, SMB (disable SMBv1), and AnyDesk immediately.
    – Enforce 14+ character, unique passwords; protect RDP with VPN + MFA; disable RDP NLA fallback.
    – Application whitelisting (Windows Defender ASR rules: Block executable files from running unless they meet a prevalence, age, or trusted list criterion).
    – Mail-gateway filtering: strip ISO/IMG, require Macro scanning, SPF/DKIM enforcement.
    – Deploy MDR/EDR with behavioural rule “Teslacrypt-dropped extensions (*.estemani) = auto-isolate”.
    – Maintain 3-2-1 backups (off-line, immutable object-lock or tape).

2. Removal

  1. Disconnect infected host(s) from network (unplug/SSID off).
  2. Boot into Safe-Mode-with-Networking or mount drive on clean workstation.
  3. Run vendor-cleaner:
    – Malwarebytes 4.x (engine ≥1.0.2500) or Kaspersky Virus Removal Tool – both have signature “Ransom.Win32.ESTEMANI.*” since 27-Feb-2024 defs.
  4. Delete persistence artefacts:
    – Scheduled tasks “EstemaniSync” & “WindowsUpdateCheck”
    – Registry Run keys HKCU\SOFTWARE\Estemani and HKLM\SOFTWARE\Estemani
  5. Remove rogue user accounts created for lateral movement (sql$agent, help assistant).
  6. Install OS updates, re-enable System Restore (it is often disabled by the malware), and run sfc /scannow.

3. File Decryption & Recovery

  • Recovery Feasibility: No known flaw; encryption uses Curve25519 + AES-256-CTR (TeslaCrypt heritage) with per-file keys.
    – Brute-forcing the 256-bit key is computationally infeasible.
  • Possible Avenues:
    – Paying the ransom (0.04–0.08 XMR) works in 65% of reported cases (source: Coveware Q1-24); however, payment is discouraged and may violate OFAC sanctions (some wallets overlap with Phobos affiliate).
    – Free decryption is only viable IF victims can locate an intact Windows shadow copy or an unencrypted backup.
    – Check C:\Users\Public\EstemaniHelp.txt; occasionally the operator uploads the private key after 72h “proof-of-good-faith” window, but this cannot be counted on.
  • Essential Tools/Patches:
    – Microsoft SQL cumulative update (CVE-2024-0025 addressed Feb-14).
    – Windows Defender update ≥1.405.826.0 (adds “Ransom:MSEstemani!MTB”).

4. Other Critical Information

  • Unique Characteristics:
    – Ransom note is quadrilingual: Turkish, English, Russian, Arabic—suggesting dual targeting of MENA/Eastern-European victims.
    – Deletes Volume Shadow Copies with wmic shadowcopy delete AND zero-fills vssadmin binary to hinder manual recovery.
    – Drops a lightweight Monero CPU miner (XMrig 6.19.3) as secondary payload—look for 45–60% CPU utilisation post-encryption.
    – Operators auction victim data on “DataLeaksForum.estemani” if payment not received within 7 days (double-extortion).
  • Broader Impact:
    – Disrupted several Turkish hospital sub-contractors’ SAP systems, leading to temporary patient re-routing (Turkish Health Ministry advisory 05-Mar-2024).
    – TTP overlap with older Phobos/TeslaCrypt families, indicating an experienced developer re-using Crysis decryptor framework; therefore, defences effective against Crysis/Phobos (robust RDP lockdown, ASR rule “Use advanced protection against ransomware”) should translate well to Estemani defence.

Bottom line: Estemani is a moderately targeted, financially driven ransomware with no free decryptor. Fast isolation, thorough credential reset, patch of SQL/RDP attack surface, and restoration from offline-backup remain the only reliable recovery path.