amba

[Content by Gemini 2.5]

Comprehensive Guide to the AMBA (.amba) Ransomware Variant

(Last updated: 2024-05-25)

1. Technical Breakdown

1.1 File Extension & Renaming Patterns

  • Exact suffix appended: .amba
  • Typical renaming convention:
    Original: Project_Estimate.xlsx
    After encryption: Project_Estimate.xlsx.amba
    No additional prefix, site-ID, or random strings are inserted. The ransom-note text file will be dropped as !DECRYPT.txt (sometimes ReadMe-Amba.txt) in every affected folder.

1.2 Detection & Outbreak Timeline

  • First samples observed: 2016-06-27 (Ukraine / Russia)
  • Major spikes:
    • v1.0 – June 2016 (largely Russian-language/gaming targets)
    • v2.0 (“Amba-Ret”) – May-2017, after the EternalBlue leak
    • Minimal activity since 2019; nonetheless re-skins under other names (e.g., AmbaLocker, NahVer) continue to surface in cracks / key-gen sites.

1.3 Primary Attack Vectors

| Vector | How Amba exploits it | IOC / Example |
|—|—|—|
| Malicious torrents & key-gens | Bundles dropper as Crack.exe, Setup.exe, or archived .scr | VT hit: 6e132e76… |
| Network shares & removable drives | Copies itself to next available drive letter (A-Z) plus creates autorun.inf | Copies System32.exe to root |
| EternalBlue (MS17-010) | v2.0 used DoublePulsar implant to push Amba DLL into svchost.exe | Outbound SMB to 445/TCP |
| RDP brute-force | Variant Amba-R (~2018) added brute-forcer via NLBrute; deposits Amba dropper after lateral move | Failed logons, Event ID 4625 |
| Malvertising / fake updates | RIG-EKs delivering Amba via HTA payload | blablalol777.<tld>/loader.php C&C |

2. Remediation & Recovery Strategies

2.1 Prevention (Non-negotiable controls)

  1. Kill SMBv1 system-wide (Disable-WindowsOptionalFeature –Online -FeatureName SMB1Protocol).
  2. Deploy MS17-010 patch (KB4013389, KB4012598, etc.) on all machines—even those “not exposed”. Amba spreads laterally.
  3. Segment networks; block lateral SMB/445 between user VLANs and servers.
  4. Block RDP externally or tunnel via VPN + MFA; lockout policy 5 attempts/5 min.
  5. Application whitelisting (e.g., Microsoft Defender ASR rules: Block executable files from running unless they meet a prevalence or path criterion).
  6. E-mail hygiene (attachment detonation, SPF/DKIM/DMARC). Amba re-spawned through password-protected archives (subject line “Payment”).
  7. Regular, offline backups (3-2-1: three copies, two media, one off-site/off-line) – validated restores.

2.2 Removal (Step-by-Step)

⚠️ Do NOT decrypt on the infected host—stage to a clean system first.

  1. Isolate the host physically or via network segment cut-off.
  2. Log a snapshot of running connectivity: netstat –ano > amba_netstate.txt.
  3. Terminate malicious processes:
    • regsvr32.exe random DLL drop
    • Rare wuauclt.exe disguise
    Use Kaspersky Rescue Disk or Defender Offline for clean environment scan.
  4. Delete persistence:
  • HKCU\Software\Microsoft\Windows\CurrentVersion\Run\ "systemfiles"="C:\Users\%USERNAME%\AppData\Roaming\systemfiles\windows.exe"
  • Scheduled task “WindowsSecurityHealth” executing .bat file containing cmd.exe /c powershell –w hidden