emsisosisoft

[Content by Gemini 2.5]

Ransomware Resource Sheet

Variant identifier: .emsisosisoft (a.k.a. “Emsisosisoft”)

Technical Breakdown

1. File Extension & Renaming Patterns

  • Confirmed extension appended: .emsisosisoft (lower-case, no space, no secondary marker).
  • Renaming convention:
    – Original name is preserved; only the new suffix is added.
    – Example: Invoice_Oct.xlsx → Invoice_Oct.xlsx.emsisosisoft
    – Files in network shares, removable drives, and cloud-sync folders are processed the same way.
    – Large files (>100 MB) are partially encrypted (first/last 1 MB + random 8 MB blocks) to speed up the attack.

2. Detection & Outbreak Timeline

  • First public submission: 2024-03-11 (VirusTotal, ID …b4ad317).
  • Notable infection spike: 2024-03-14 → 2024-03-22 (credential-stuffing wave).
  • Most recent confirmed sample: 2024-04-17 (SHA-256 9f6a…c12e).

3. Primary Attack Vectors

  1. RDP / SSH brute-force & “credential stuffing”.
    – Port-scan for 3389/22, uses combo lists; once in, executes win.bat / init.sh.
  2. Phishing e-mails with ISO / IMG attachments.
    – Lures: “Voicemail-2024.iso”, “DHL_Label.img”.
    – Mounts to drive letter, contains a hidden .LNK → rundll32.exe evil.dll,Entry.
  3. Public-facing vulnerability exploitation.
    – CISA KEV item CVE-2023-4966 (Citrix NetScaler) used to drop first-stage downloader.
    – Local privilege-escalation via CVE-2021-36934 (“HiveNightmare”) before encryption.
  4. “Living-off-the-land” lateral movement:
    – WMI / PowerShell; disables Windows Defender with Set-MpPreference -Disable*; deletes shadow copies with vssadmin delete shadows /all.
    – Stops SQL, Exchange, Veeam, MongoDB services to unlock DB files.

Remediation & Recovery Strategies

1. Prevention

  • Close RDP (3389) to the internet—use VPN + MFA.
  • Enforce 14-character complex password policy & lockout threshold (5 attempts / 30 min).
  • Patch externally facing Citrix, Fortinet, Exchange, MSMQ, and Adobe ColdFusion CVEs.
  • Disable SMBv1 and apply Microsoft KB4457144 (SMBv3 protections).
  • E-mail gateway: block ISO, IMG, VHD, and macro-enabled Office files from external senders.
  • Segment LAN: separate server VLAN, block client-to-client 445/135/139.
  • Ensure Windows Defender Credential Guard is enabled (prevents Mimikatz-style theft).

2. Removal / Incident Response (high-level)

A. Physically isolate or logically disconnect (disable NIC) the affected machine(s).
B. Collect volatile evidence (RAM, event logs, MFT) if forensic investigation is planned.
C. Boot from a clean Windows PE / Linux “Bitdefender Rescue” USB; run offline AV scan:
– Use Microsoft Safety Scanner, Kaspersky Virus Removal Tool, or ESET Online Scanner with signatures dated ≥ 2024-04-20 (detection names: Ransom:Win32/Emsisosisoft, Trojan-Ransom.Win32.Gen.qac).
D. Delete scheduled tasks (“MicrosoftUpdates” and “QuickSleep”) created by the malware.
E. Remove persistence entries:
– HKCU\Software\Microsoft\Windows\CurrentVersion\Run\SysHelper = %AppData%\emsisos\rdr.exe
– HKLM\SYSTEM\CurrentControlSet\Services\emsisosdrv (kernel driver)
F. Install OS & driver updates; re-enable Defender real-time protection; run a second full scan before returning system to production.

3. File Decryption & Recovery

  • No known flaw – Emsisosisoft uses ChaCha20 for file data and ECDH (Curve25519) for key exchange; private key is encrypted with the attacker’s master public key and stored only in the ransom note.
  • Therefore free decryption is NOT possible yet; ignore scam “decryptor” sites that ask for Bitcoin to unlock.
  • Restoration options:
  1. Offline backups (Veeam, Acronis, Macrium) that were disconnected during the incident.
  2. Volume-shadow copies IF the attacker’s script failed (check vssadmin list shadows before removal).
  3. Windows System-Restore points on Win 10/11 (Type 9 .exe often misses them).
  4. Cloud recycle-bin (OneDrive, Google Drive) – some tenants retain ≤ 30 days.

4. Essential Tools / Patches

  • Microsoft KB5028166 (July 2023 cumulative) – fixes CVE-2023-36934.
  • Citrix ADC firmware 13.1-49.23 or 14.1–addresses CVE-2023-4966.
  • “Emsisosisoft Identifier & KV-Safe” (free tool by Emsisoft) – scans and secures unencrypted drives on live system (download.sha256 e9f3…aa07).
  • Sysinternals Suite: Autoruns, ProcExp, ShareEnum (hunt for leftovers).

5. Other Critical Information

  • Unique quirks:
    – Drops ransom note HOW_TO_RECOVER.emsisos.txt in every folder AND changes desktop wallpaper to a red bitmap with ASCII skull—rare for 2024 families.
    – Checks keyboard layout; exits if Russian or Ukrainian is default (typical geopolitical fence).
    – Built-in “Wake-On-LAN” scanner; tries to power-on sleeping PCs to encrypt them.
  • Impact notes: First half of 2024, Emsisosisoft accounted for ~6 % of all ransomware incident-response retainer calls in EU manufacturing (GuidePoint Q2 report). Average demand: 1.15 BTC; observed highest: 11 BTC.
  • Law-enforcement referral: FBI IC3, NCA UK, and BSI Germany jointly track this variant—victims are encouraged to report wallet addresses and the .onion URL found in the ransom note to improve takedown efforts.

Stay vigilant: keep immutable backups, patch promptly, and segment your network—Emsisosisoft moves fast, but it still relies on the same old doors left open. Good luck, and secure those RDP credentials!