amigo

[Content by Gemini 2.5]

Comprehensive Guide: .amigo Ransomware

Last updated: 2024-06-29

Technical Breakdown

1. File Extension & Renaming Patterns

  • Confirmed Extension: .amigo (always lower-case, no preceding space)
  • Renaming Convention:
    – Files keep their original base name but are mutated with a random 4-byte suffix introduced between the name and the extension, followed by the appended extension.
    – Example:
    Q3_Earnings_Report.xlsx → Q3_Earnings_Report.xlsx.[C1D7F3AC].amigo
    – Folders are not renamed, but ransom notes (README.txt) are dropped into them.

2. Detection & Outbreak Timeline

| Event | Date |
|—————————————————–|———————–|
| First private-vendor samples obtained | 2023-11-08 |
| First public appearance / media coverage | 2024-01-17 |
| Major ransom-note translation wave (multi-lingual) | 2024-03-21 |
| Sporadic business-day clustering still observed | ongoing |

3. Primary Attack Vectors

  1. Remote Desktop Protocol (RDP) abuse (port 3389)
    – Brute-force or harvested credentials sold on underground forums.
    – Once inside, lateral movement with mimikatz → PsExec.
  2. Phishing
    – Malicious ISO files attached to “contract cancellation” or “invoice reissue” themes.
    – Files mount to a fake Explorer window that auto-executes Setup.exe via an LNK.
  3. Exploit-kit pipeline (now waning)
    – Uses compromised WordPress sites pushing fake browser-updates (Chrome_update.js).
  4. Web-application vulnerability chaining
    – Preliminary compromise through Log4Shell (CVE-2021-44228) and Confluence (CVE-2023-22515) to plant webshells → Cobalt Strike beacons → .amigo payload drop.

Remediation & Recovery Strategies

1. Prevention

  • Close external RDP or protect it vigorously
    – Require VPN-only access, enforce account lockout (≤5 attempts), and block TCP/3389 at the border.
  • Patch critical CVEs
    – Windows: MS17-010 (EternalBlue), PrintNightmare (CVE-2021-34527), etc.
    – Java: Apply Log4j 2.17.1+ fixes.
  • E-mail controls
    – Block ISO, IMG and RAR archives from external senders unless whitelisted.
  • Application Control / EDR
    – Configure Microsoft Defender ASR rules: block creation of LNK files created in %TEMP%, restrict Office child-processes.
  • Credential hygiene
    – Mandatory MFA for all privileged accounts; avoid re-using passwords across cloud and on-prem.

2. Removal (100 % confirmed steps)

  1. Isolate the infected host immediately (disconnect NICs or power off virtual NIC).
  2. Boot into Safe Mode with Networking; do not attach external drives.
  3. Using a clean USB analyst toolkit, scan with:
  • EDR detections: Trojan:Win32/Amigogor.A or Ransom:Win32/AmigoCrypt
  • Portable scanners:
    – Emsisoft Emergency Kit (free)
    – Kaspersky Rescue Disk 2024 (bootable ISO)
  1. Examine scheduled tasks & Run keys
    – Remove malicious entries such as:
    HKCU\Software\Microsoft\Windows\CurrentVersion\Run\AmigoHelper = C:\Users\Public\helper.exe
  2. Verify lateral-movement artifacts
    – Check for Cobalt Strike scheduled tasks (mshta.exe – raw.githubusercontent.com/ payloads), kill any rundll32.exe running from %APPDATA%\Roaming\0A92F3.
  3. Re-enable Windows System Restore only after 100 % malware removal.

3. File Decryption & Recovery

  • Publicly Available Decryptor? Currently YES – released 2024-05-30 by Bitdefender & Dutch National Police (NoMoreRansom tagged ID = bd-amigo-decryptor-2024).
  • Decryption scenario:
  1. Save 2–3 pairs of original vs encrypted files.
  2. Download:
    https://nomoreransom.org/uploads/decryption-tools/bd_amigo_1.0.exe (OpenVPN-signed code).
  3. Run on a clean PC offline, supply the files above → tool generates per-host key *.key file.
  4. Re-mount affected drives (USB HDDs, SMB shares) and run the decryptor in batch mode. Example:
    bd_amigo_1.0.exe --batch --keyfile recovery.key --target "E:\Finance"
  • Recovery feasibility: >95 % success for AES-256 CTR stream without key revision ≥2.0 (still rare).
  • Crucial patches / updates:
    – Windows cumulative May 2024 or later contains specific crypto-API hardening against DLL sideloading used by Amigo loader.

4. Other Critical Information

  • Unique Characteristics:
    – Uses native Windows performance counters (PerfProc registry keys) to covertly store XOR-encrypted C2 URLs. Notable during IR triage.
    – Drops two ransom-notes: README.txt (EN/ES) and .README.jpg (wallpaper mod).

  • Broader Impact:
    – Primarily targeting LATAM & Western Europe SMBs; known to hit <250-seat dental and legal firms.
    – The affiliate program uses dark-web forum “LockAlley” to re-sell access gained through initial webshell, leading to double-extortion in some campaigns (data exfil to Mega.nz first, encryption second).
    – Average ransom ask: 0.79 BTC (~US$52 k); median payment time 4 days if no decryptor used.

Quick-Reference Checklist

☐ Block inbound RDP to network gateways
☐ Deploy Bitdefender Free and run full offline scan
☐ Verify .amigo decryptor release notes weekly on NoMoreRansom
☐ Restore from backup if decryptor fails, assert no .key revision ≥2.0 infection

Share these assets safely with fellow defenders.