anon_by

[Content by Gemini 2.5]

Technical Breakdown – ANONBY Ransomware (file-marker “.anonby”)

1. File Extension & Renaming Patterns

• Confirmation of File Extension: Every file held to ransom receives the fixed suffix .anon_by (double-ext. if the original file already had one, e.g., report.xlsx.anon_by).
• Renaming Convention: Files retain their original base name; no prefix or additional tokens are prepended. Directory names are NOT touched, but inside every encrypted directory ANON_BY drops two identical ransom notes:
README_DECRYPT.txt (ANSI) and README_DECRYPT.html (HTML, nicer formatting).

2. Detection & Outbreak Timeline

• First Sighting: April-May 2023 (underground RAMP forum marketing); mainstream telemetry recorded clusters on 2023-06-14 in EMEA manufacturing verticals.
• Major Campaign Waves:
– Jun-Aug 2023: VMware ESXi/ vCenter compromise via CVE-2021-21974 (ESXi SLUI heap-overflow).
– Oct-Nov 2023: Mass RDP brute-forcing combined with reverse-proxy “Ngrok tunnelling” to avoid IP blacklists.
– (Ongoing) Q1-Q2 2024: Affiliate supply-chain deployment through pirated software installers (AutoCAD cracks, KMS-activator packs).

3. Primary Attack Vectors

  1. External RDP exposure (TCP/3389) protected only by user-supplied weak passwords → lateral movement via psexec, wmic, PowerShell remoting.
  2. CVE-2021-21974 & CVE-2021-21985 for un-patched ESXi/ vSphere – leads to privileged Linux compromise of hypervisor, then simultaneous encryption of all mounted VMDKs via custom TA-Linux/Golang build.
  3. Malicious email attachments: weaponized OneNote files (.ONE) with embedded HTA or ISO → PowerShell drops the main ANON_BY binary (void.exe).
  4. Software supply-chain: trojanised MSI/EXE installers posted on popular crack/warez forums. The installer runs regsvr32 /s anon_by.dll to sideload the main payload.
  5. Living-off-the-land: leverage Windows’ own certutil to base64-decode the malware second stage from an included ransom note.

Remediation & Recovery Strategies

1. Prevention

Immediate defensive hardening:
• Patch all VMware ESXi/vSphere hosts → vCenter & Hypervisor must be on ≥7.0 U3k (or migrated to 8.x).
• Disable SMB v1 globally (GPO: “Turn off SMBv1 Server & Client”).
• Enforce RDP Network-Level-Authentication, MFA, and strong passwords; disable RDP from public networks or restrict to VPN only.
• Use application whitelisting/AppLocker to blacklist liberal script execution (*.ps1, regsvr32 without path).
• Phishing-resistant MFA on all mailboxes + mail-filtering policies to block external ONE/ISO/HTA extensions.
• Immutable, off-site backups (object-lock S3/B2/SPI, tape, or Veeam hardened repository).

2. Removal

Step-by-step incident cleanup:

  1. Isolate
    • Physically network-segment or shut off all compromised machines/esxi hosts to curtail worming.
  2. Triage
    • Capture RAM dump & full disk images (DD/E01) before any remediation (legal/prosecution).
  3. Kill Persistency
    • In Windows: Delete the registry Run key HKCU\Software\Microsoft\Windows\CurrentVersion\Run\VoidLiftSvc.
    • In ESXi: Power-off all affected VMs → boot from recovery ISO/USB → mount system volumes and remove the dropped Linux executable /tmp/.void-upgrade.
  4. Credential Reset
    • Force-reset every local admin/service account from a known-clean domain controller.
  5. AV/EDR Signature/Behavioral Scan
    • Scan with updated footprint hashes (current defs: Trojan:Win32/ANonBy or Ransom.ANON).Sophos defines it as Troj/Ransom-GCQ.
  6. Rebuild/Re-image (or restore from backup).

3. File Decryption & Recovery

A. Available decryptor?
– YES. ANON_BY reuses the Babuk/Chaos-derived ChaCha20+ECDSA key scheme but does NOT correctly implement key destruction on disk.
– A free decryptor released by Emsisoft (v1.2, SHA256:5e20f116…) operates on keys leftover in %PROGRAMDATA%\WindowsApp\ (file name: key.dat) or by using an available master.private leaked after one affiliate’s arrest.

B. Fallback (Backup route)
– None of the *.anon_by files can be brute forced; decryption requires the proper key key.dat or the master ECDSA pair. If the keys are missing, restore from recent backups (offline, immutable).

Tools to download & stage ahead of an incident
• Emsisoft ANON_BY-Decryptor & accompanying readme.instructions.pdf.
• CrowdStrike Falcon Rushlock IOC list (CSV).
• VMware vSphere 78719 kb patch bundle (CVE-2021-21974 fix).
• Windows Server 2022 May-2024 cumulative patch (contains SMBv1 hardening & domain trust mitigations).

4. Other Critical Information

• Unique traits:
– 64-bit ESXi ELF variant; first historical occurrence of ransomware simultaneously locking >100 VMs across an ESXi cluster in under 2 minutes (parallelised ChaCha20 stream mode).
– Built-in anti-debug trick using VMware backdoor IO Port 5658 to detect hypervisor introspection; fails silently inside VMware Workstation/VirtualBox to avoid malware analysts.
– Ransom notes point to a private ZeroBin instance for leak negotiation—no public DLS; nevertheless 20 GB of client HR data from a German firm surfaced on “Mega.nz” in December 2023, confirming 2-fold extortion.

• Broader Impact:
– EMEA manufacturing supply-chain downtime (average outage 12–17 days; cost >100 M€).
– Raised urgency for NIS-2 directive compliance: several German & Austrian hospitals (targeted Oct 2023) adopted immediate patch-deadline clauses for their VMware clusters.

By combining strict patching timelines, zero-trust remote access controls, immutable backups, and the freely available decryptor, organizations can substantially limit the blast radius of ANON_BY ransomware.