asasin

[Content by Gemini 2.5]

Asasin Ransomware Comprehensive Guide

(Last updated: 2024-10-XX)

Technical Breakdown

| Element | Details |
|———|———|
| File Extension & Renaming Patterns |
| Confirmation of File Extension | .asasin (lower-case) appended to every encrypted file. |
| Renaming Convention | Single, straight append only—report.docx → report.docx.asasin. No random suffixes or e-mail addresses placed inside the new name. |
| Detection & Outbreak Timeline |
| Approximate Start Date/Period | Frist publicly observed in June 2017 as part of the Locky v2 re-branding wave. Widespread via the Necurs botnet spam blitz that ran through September 2017 and sporadic re-appearances since. |
| Primary Attack Vectors |
| Propagation Mechanisms | 1. Mass-delivered phishing mails with renamed ZIP files (asasin.zip, invoice_123.pdf.zip) containing weaponised .vbs, .js, or .lnk droppers.
2. EternalBlue (MS17-010) + DoublePulsar for lateral movement after initial foothold on unpatched SMBv1 servers.
3. Weakly-secured RDP or VNC reconnaissance followed by credential stuffing.
4. Exploits of exposed SMB shares on port 445 in older Windows environments (Windows 7, Server 2008 R2). |

Remediation & Recovery Strategies

1. Prevention

| Risk | Mitigation |
|——|————|
| Malicious e-mail | ● Block .js, .vbs, .wsf, .jse, .lnk, and macro-enabled Office files at the gateway.
● Enforce SPF + DKIM + DMARC and continuously train users on phishing drills. |
| SMBv1 / EternalBlue | ● Disable SMBv1 via GPO immediately (Set-SmbServerConfiguration –EnableSMB1Protocol $false).
● Apply MS17-010 and all subsequent Windows cumulative updates. |
| RDP brute-force | ● Restrict RDP to VPN-only or Zero-Trust access.
● Enforce NLA + account lockout policies.
● Change default 3389/TCP port (obfuscation only) and log to SIEM. |
| General hygiene | ● Least-privilege user accounts, application whitelisting (AppLocker / Windows Defender Application Control). |
| Offline backups | ● Daily air-gapped backups verified and stored off-site or in S3 with Object-Lock. |

2. Removal

Within the first 48 h after infection:

  1. Isolate the host: yank network cable or disable adapters to contain lateral spread.
  2. Map the scope: review IR logs, EDR telemetry, and firewall/netflow for the “Patient-0” machine.
  3. Collect forensic image: if legal/regulatory evidence is required.
  4. Boot into Safe Mode with Networking:
    – bcdedit /set {current} safeboot network
    – Remove the following artifacts created by Asasin:
    • %APPDATA%\winasas.exe (packer)
    • %TEMP%\_TMP*.bat launch scripts
    • Run-keys in HKCU\Software\Microsoft\Windows\CurrentVersion\Run\winasas
  5. Update AV signatures & run a full scan: All Tier-1 vendors detect this variant (e.g., Microsoft Defender as Ransom:Win32/Locky.A).
  6. Harden & patch: ensure the Jun-2017 cumulative update package is installed and SMBv1 disabled.
  7. Reboot normally once confirmed clean.

3. File Decryption & Recovery

Recovery Feasibility | Tool / Strategy
——————– | —————-
Decryption NOW | Impossible – Asasin re-uses the Locky/AES-128 + RSA-2048 hybrid scheme. Victim’s private key always resides exclusively on the attacker’s C2.
Workarounds |
• Check for Shadow Copies: vssadmin list shadows – Asasin/VSSadmin is usually called to purge shadows, but sometimes partial volumes survive.
• Restore from Backup: Air-gapped or immutable backups (wasabi, veeam hardened repositories). Test non-corruption before bulk restore.
• Volume-shadow retrieval tools: ShadowExplorer, recuva deep scan, or ProDiscover (forensic toolset) against unmounted VSS store on external disk cloned via dd.
• Occasional Key Leaks: In Jun-2018, a Pastebin dump containing ~24 000 private keys linked to a prior Locky campaign circulated. locky_decryptor.exe (Kaspersky and Bitdefender) can scan if the derived key for your victim-ID exists.

4. Other Critical Information

Attribute | Notes
——— | —–
Cryptographic Twist | If execution detects Cyrillic keyboard layout (GetSystemDefaultLCID=0x419), the payload self-terminates immediately, although the spamming infrastructure still serves the same binaries to that region.
Ransom Note | Drops asasin.htm on Desktop and in every encrypted directory with payment instructions over Tor and a victim-ID (e.g., C4C7C4A4CEA33F5D). The Tor address rotates every campaign wave.
Wider Impact | Part of the larger Locky franchise that extorted an estimated US$7–US$8 M in Bitcoin across 500 000+ unique cases. Entities in healthcare, law offices, and manufacturing were disproportionately affected in the late-2017 resurgence.

Essential Tool Checklist

  • Offline-as-a-Service Windows cumulative patches → https://catalog.update.microsoft.com
  • SMBv1 disable script (.ps1) → https://raw.githubusercontent.com/neosmart/SMBv1-disable/master/Disable-SMBv1.ps1
  • LockyDecryptor (when victim-id matches leaked key set) → bitdefender-labs-v1.1.zip
  • Kaspersky’s RannohDecryptor – supports AES-NI accelerations for Locky variants if local test-vector detected.
  • Veeam or Zerto immutable backup appliances with object-lock >30 days.
  • MS17-010 network scanners (nmap smb-vuln-ms17-010.nse) to close the loop.

Key Takeaway

Asasin is essentially “new lipstick on an old Locky pig”: same encryption, same bugs, zero decryption. Your single best defence is a tested air-gapped, immutable backup combined with strict e-mail sandboxing and hardened SMB/RDP posture.