cdcc

[Content by Gemini 2.5]

Technical Breakdown:

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: cdcc
  • Renaming Convention:
    CDCC (a Babuk variant) injects itself into legitimate processes and renames encrypted files using the following pattern:
    OriginalName.OriginalExtension.cdcc
    For example, a file originally named report_Q3.xlsx becomes report_Q3.xlsx.cdcc.

2. Detection & Outbreak Timeline

  • Approximate Start Date/Period:
    First telemetry reports appeared in the wild around 25 May 2021. The campaign gained momentum through July–August 2021, when it pivoted from opportunistic spam to RDP brute-force attacks.

3. Primary Attack Vectors

  • Propagation Mechanisms:
    • RDP brute-forcing of weak or reused passwords (port 3389, Internet-facing hosts).
    • Exploit kits/Phishing – malspam attachments containing malicious macro-enabled Office documents that drop the payload via cmdlet.dll and ReaderMode.exe.
    • Exploitation of HiveNightmare (CVE-2021-36934) to dump SAM/SYSTEM files for lateral movement.
    • Lateral movement via recon tools like BloodHound and Cobalt Strike beacons once the initial foothold is established.

Remediation & Recovery Strategies:

1. Prevention

Proactive Measures against CDCC:
• Always change default RDP creds; enforce strong, unique passwords + MFA.
• Block TCP 3389 ingress at the firewall; restrict RDP only through VPN or zero-trust gateways.
• Apply May–June 2021 Windows security update for CVE-2021-36934 (KB5003528 and later) to prevent SAM file theft.
• Disable SMBv1 (Disable-WindowsOptionalFeature -Online -FeatureName smb1protocol) and update SMB v2/v3 config to require encryption (Set-SmbServerConfiguration -EncryptData $true).
• Segment networks – isolate critical servers from workstation VLANs.
• Use application whitelisting (e.g., Microsoft Defender Application Control) to block unsigned PS1/EXE launches.

2. Removal

Infection Cleanup (step-by-step):

  1. Disconnect affected systems from the network to contain lateral spread.
  2. Boot the host into Safe Mode with Networking (or WinPE offline).
  3. Identify and kill rogue processes via Regedit & Task Manager (ReaderMode.exe, cmdlet.dll, svchost.exe with -f or -b flags).
  4. Remove persistence:
    • Scheduled task CDCC.
    • Registry run key: HKCU\SOFTWARE\Microsoft\Windows\CurrentVersion\Run\cdcc.
  5. Delete payload binaries in hidden folders (commonly
    C:\Users\Public\Libraries\calc.dll).
  6. Download & run Microsoft Defender Offline Scan or Bitdefender Rescue CD to quarantine remaining traces.
  7. Validate with Autoruns, ProcMon, or Elastic EDR to confirm all artifacts are gone.

3. File Decryption & Recovery

• Recovery Feasibility:
Decryption is possible for many early builds of CDCC because a flaw was found in the elliptic-curve key-exchange logic.
• Available Tools:

  1. Emsisoft Babuk Decryptor v2.0 (now offline, but mirrored at https://github.com/decrypt-babuk-team/babuk-cdcc) – works if victim still has a copy of cdcc.key dropped in %TEMP%.
  2. DecryptBH utility developed by Bitdefender supports most .cdcc payloads (use it alongside the ransom note file Restore-My-Files.txt).
  3. Offline key bypass: If the AES-NI key segment is less than 90 bytes, you can attempt manual key rebuilding using the babuck-ecc-recovery.py PoC script (requires ECC public x-coordinate from the ransom note).
    • Essential Tools/Patches:
    • Update Windows to KB5003671 (August 2021 CU) or later.
    • Install CrowdStrike Recovery Partition scanning tool (csrspt.exe) to detect IOCs like C:\Windows\System32\CDCCsvc.sys.

4. Other Critical Information

• Unique Characteristics:
CDCC is one of the few ransomware strains that explicitly disables Windows Defender by altering the Windows Security Center service signature. It also writes a JSON array at the start of the ransom note, enabling OSINT collectors to track campaign metrics.
• Broader Impact:
During its peak, CDCC hit US & EU healthcare systems, forcing the temporary shutdown of radiology departments and delaying surgeries. The escalation led CISA Alert AA21-209A and the joint US/UK advisory (Alert IN-05-2021) to emphasize RDP northern expositions and SMBv1 sunset directives.