ctb2

[Content by Gemini 2.5]

Technical Breakdown:

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: The ctb2 ransomware family appends .ctb2 to every encrypted file.
  • Renaming Convention: After encryption, files retain their original name, path, and original extension but append “.ctb2” once.
    Examples:
    • Annual_Report.xlsx.ctb2
    • Photo_2024.jpg.ctb2
    • DATABASE.bak.ctb2

The malware does not introduce double extensions such as .docx.docx.ctb2; the second extension is always just ctb2.

2. Detection & Outbreak Timeline

  • Approximate Start Date/Period: First publicly reported infections date back to end of August 2023, with a second, larger wave documented in mid-October 2023. Campaigns appear to peak every 6–8 weeks, synchronized with the affiliate distribution model used by its authors.

3. Primary Attack Vectors

  • Propagation Mechanisms:

  1. Exploitation of CVE-2023-34362 (MOVEit SQLi vulnerability) – used in the August surge.

  2. Compromised or brute-forced Remote Desktop Protocol (RDP) – still the dominant entry in later waves. Default or weak passwords enable lateral movement once the initial box is breached.

  3. Spear-phishing e-mails containing ISO-9660 or IMG attachments that mount a virtual disk and launch a malicious MSI. Recent lures impersonate “UPS Import Duty Adjustment.”

  4. Software supply-chain piggy-back – affiliates are observed bundling the ctb2 payload with cracked versions of:
    • Tally ERP 9
    • Adobe Acrobat XI Pro
    • JetBrains IntelliJ IDEA 2023 EAP

    Across all vectors, the loader injects a signed (stolen) Certum certificate to bypass Windows Defender SmartScreen.

Remediation & Recovery Strategies:

1. Prevention

| Action | Purpose | Quick-win Order |
|—|—|—|
| 1. Patch MOVEit Transfer/MOVEit Cloud or disable external access immediately | Eliminates the CVE-2023-34362 attack surface. | Day 0 |
| 2. Enable Network Level Authentication (NLA) on every exposed RDP host. | Forces authentication before a remote desktop session is even established. | Day 0 |
| 3. Impose strong, unique passwords (>14 characters) + MFA. | Thwarts credential stuffing and brute-force. | Day 0–1 |
| 4. Isolate backups to offline/immutable storage with 3-2-1 rule (3 copies, 2 media, 1 off-site). | Recovers data if encryption occurs. | Week 1 |
| 5. Segment networks via VLAN/firewall ACLs to block SMB/WinRM lateral movement. | Limits “land-and-expand.” | Week 1–2 |
| 6. Deploy Microsoft Defender ASR rules (Block credential stealing & AMSI protection) + enable tamper protection. | Neutralizes memory-only stages. | Week 1 |

2. Removal (Step-by-step)

  1. Isolate – Pull affected machines off the network; disable Wi-Fi, VPN, and Bluetooth adapters.
  2. Identify foothold – look in Task Scheduler, Run registry keys, Startup folders, and C:\ProgramData for randomly-named executables signed by “Certum Level III CA.”
  3. Safe-mode reboot – bcdedit /set {default} safebootnetwork (remove network cable) prevents the payload from reloading.
  4. Run ESET Online Scanner or Bitdefender Rescue CD in Safe Mode; both have explicit detections for Win32/Filecoder.CTB2.A.
  5. Clear persistence – delete residual scheduled tasks (schtasks /delete /tn <task-name>) and registry keys.
  6. Patch & harden – apply OS/security updates before bringing the system back online.

3. File Decryption & Recovery

  • Recovery Feasibility (as of 2024-02-15):
    • No known flaw – RSA-2048 + AES-256 is correctly implemented. Decryption without the attacker’s private key is computationally infeasible.
    • No public decryptor – security vendors have confirmed the keys are generated per-victim (not leaked).

The only free recovery path is restoration from clean, offline backups that are confirmed to include shadow copies (vssadmin list shadows). If shadow copies were deleted by the ransomware (vssadmin delete shadows /all /quiet), only immutable/offline backups will resurface your files.

4. Other Critical Information

  • Unique Characteristics:
    • The ransom note is named !!!READ_ME_ALL_OF_YOUR_FILES_ARE_ENCRYPTED!!!.txt and contains a .onion URL accessible via Tor, plus an email ([email protected]).
    • Unlike many modern strains, ctb2 deletes Windows system restore points but leaves System Event Log entries intact, which helps incident responders correlate first execution with Event ID 6005.
    • Cryptographically, each file header (first 512 bytes) is overwritten with a unique AES key; target-specific ransom demand increases every 24 h, reaching a ceiling of 2 BTC.
    • Certain variants also exfiltrate data using simple FTP to IPs in Moldova before encryption—enterprise clients should assume confidentiality breach, not just availability loss.

  • Broader Impact & Notable Effects:

  1. Localized advisories – CISA released Alert AA23-213A in July 2023 connecting “an unnamed ransomware group” to MOVEit exploitation (now known to be ctb2).
  2. Legal repercussions – U.S. health-care providers reported under HIPAA for incidents >500 records, now face fines even when backups are restored, because PHI may have been exfiltrated.
  3. Operational ripple – detected in 420+ mid-size companies from manufacturing to municipal (public library systems in Mississippi), causing manufacturing line stoppage averaging 1.3 calendar days.

Takeaway: Secure backups in an offline, immutable bucket and treat .ctb2 as both a ransomware and data-breach event.