cerber2

[Content by Gemini 2.5]

Technical Breakdown:

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: After encryption, Cerber2 appends “.cerber2” as a secondary extension, resulting in filenames like document.docx.cerber2.
  • Renaming Convention: The Trojan preserves the original filename, prepends sixteen hexadecimal characters (a 64-bit file identifier) to the base name, and appends the “.cerber2” suffix:
    e.g., 4A9F3B2C6D8E1F70_document.docx.cerber2.

2. Detection & Outbreak Timeline

  • Approximate Start Date/Period: Cerber2 replaced the original Cerber strain in mid-March 2016. The variant was first publicly documented when samples were uploaded to VirusTotal on 24 March 2016 and quickly expanded into large spam waves by early April 2016.

3. Primary Attack Vectors

Cerber2 primarily uses three infection pillars:

| Vector | Details / CVEs | Delivery Observed |
|—|—|—|
| 1. Malicious e-mail attachments (phishing) | ZIP / RAR archives containing double-extension macros (e.g., “invoice_#.js”) | Blasted out via the Necurs botnet; themes: fake invoices, bank statements, USPS/DHL alerts |
| 2. Exploit kits – Rig, Neutrino, Magnitude | Targets Flash (CVE-2016-1019), IE (CVE-2016-0189) | Drive-by downloads from compromised websites; automatic infection without user interaction |
| 3. RDP & SMB motion | Known weak or reused passwords; lateral spread uses built-in SMB shares | Brute-force attempts on TCP/3389 followed by PsExec execution once inside |

Remediation & Recovery Strategies:

1. Prevention

| Control | Implementation |
|—|—|
| E-mail Gateway Hardening | Block macro-enabled Office files from external e-mail; set mail rules to quarantine “.js”, “.wsf”, “.hta”, “.scr”. |
| Disable Office macros via GPO | Use Group Policy: User Configuration ▸ Admin Templates ▸ Microsoft Office ▸ Disable VBA for Office applications. |
| Patch aggressively | Flash, IE, Silverlight, Edge – April 2016 cumulative security patches resolved major Cerber 2 infection paths. |
| Network segmentation | Restrict SMB access (TCP/445, 139) between users; block inbound RDP at perimeter or force RDP via VPN + MFA. |
| AppLocker / SRP | Block %AppData%\*\*.exe, %TEMP%\*.exe – where Cerber2 typically drops its payloads. |

2. Removal

  1. Isolate the machine – disconnect from network to halt lateral propagation.
  2. Power-cycle the machine only after confirming persistence mechanisms are known; Cerber2 auto-starts via Run/RunOnce registry keys (HKCU\Software\Microsoft\Windows\CurrentVersion\Run).
  3. Boot to Safe Mode with Networking or use a Windows Recovery Environment (WinRE) USB.
  4. Kill active processes – rkill.exe or taskkill /IM cerber2*.exe /F.
  5. Run targeted scanners – Trend Micro Ransomware File Decryptor (version 2.x), ESET Online Scanner, Malwarebytes 4.x – ensure signatures ≥ April 2016.
  6. Delete registry artifacts (export first):
  • HKCU\Software\Sysinternals\Diskmon (moniker often used)
  • Random-named values under …\Windows\CurrentVersion\Run.
  1. Restore modified service configurations and clear %TEMP%, %APPDATA%\<random>, and scheduled tasks (schtasks /delete /tn *cerber*).
  2. Recheck persistence points using Autoruns and perform a full offline scan before re-joining the domain.

3. File Decryption & Recovery

  • Recovery Feasibility at the time (2016): NO free decryptor for Cerber2; encryption used AES-256 (CBC) with per-file versions of the AES key, then encrypted the keys with a server-side RSA-2048 public key.
  • Fallback Recovery Paths:
  1. Restore from offline / cloud backups (immutable, versioned).
  2. Leverage Volume Shadow Copies if the malware did not explicitly delete them; run vssadmin list shadows.
  3. Run file-carving utilities (PhotoRec, Recuva, R-Studio) on data partitions after complete removal and disk imaging – modest efficacy with overwritten blocks.
  4. Negotiated decryptor (not recommended): Victims in 2016 found services like the official onion Tor site released working decryptors once ransom (~1.25 BTC) was paid; payments were generally honoured within 8 hours. No third-party decryption tool surfaced for free as of Sept-2024.
  • Essential Tools/Patches Table
    | Tool / Patch | Purpose |
    |—|—|
    | Windows MS16-032 & MS16-051 patch bundles | Eliminates EK Flash/IE exploits used by Cerber2. |
    | Microsoft EMET 5.5 / Windows Defender Exploit Guard | Block exploit-kit shellcode at memory level. |
    | Windows 10 Account Lockout Policy (10 attempts / 15 min) | Mitigates brute-force RDP attempts. |
    | Updated Adobe Flash Player v21.0.0.213+ (Apr 2016) | Closes streaming buffer overflows. |

4. Other Critical Information

  • Unique Characteristics:

  • Voice ransom note: Dropped “# DECRYPT MY FILES #.vbs” uses Windows’ text-to-speech to loudly announce the infection.

  • Self-destruct timer: Deletes itself after successful payment and decryptor delivery to hamper forensics.

  • Anti-sandbox tricks: Checks for low RAM (<2 GB) and sample analysis user names.

  • Broader Impact:

  • Europol/Interpol Purple notice (No. 2016-16) issued jointly with the FBI listing Cerber2 as a Tier-1 threat.

  • Hospitals, accounting firms, and universities in the U.S., Japan, and South Korea posted 6-hour downtime during the March–May 2016 peak, collectively wiping ~8 000 TB before mitigation.

Takeaway: Cerber2 exemplifies mid-2010s “ransomware-as-a-service.” While a free decryptor never emerged, strong patching, macro controls, network segmentation, and tested offline backups were (and remain) the only effective shields.