c1024

[Content by Gemini 2.5]

RANSOMWARE PROFILE: C1024 (April 2024 wave)

Technical Breakdown

1. File Extension & Renaming Patterns

  • Confirmation of File Extension:
    c1024 – appended verbatim without a preceding dot, e.g., Invoice_2024.pdf becomes Invoice_2024.pdfc1024.
  • Renaming Convention:
    – No extra prefix/suffix is added.
    – Directory-level marker: A file named c1024-readme.txt is dropped in every affected folder.
    – No folder-name alteration.

2. Detection & Outbreak Timeline

  • First sightings: 02-Apr-2024 (dark-web victim posts)
  • Major surge: 09-Apr-2024 onward, coinciding with a large AnglerFish-style malspam campaign.
  • Patches/Signatures released: Most AV engines added generic detection (Trojan-Ransom.Win32.C1024) on 11-Apr-2024.

3. Primary Attack Vectors

| Vector | Details / Indicators |
|———————————|————————————————————————————–|
| Malspam (biggest contributor) | ZIP attachments containing ISO or IMG files: DHL-delivery-[random].zip |
| Microsoft SmartScreen bypass| ISO includes LNK shortcut masquerading as “Unsubscribe” that launches install.bat |
| Living-off-the-Land abuse | Uses certutil -decodehex to drop backdoor, then vssadmin delete shadows |
| Lateral movement | Looks for unpatched MS17-010 hosts via SMBv1 to spread with EternalBlue |
| Stolen credentials / RDP | Pastes dumped NTDS.dit for offline cracking; brute-force on exposed 3389 |
| Open-source RATs | Drops MeshAgent for persistence before payload executes. |

Remediation & Recovery Strategies

1. Prevention

  1. Block inbound emails with .iso, .img, or .vhd attachments at the gateway.
  2. Disable .lnk execution from mounted ISOs via GPO (User Configuration → Policies → Administrative Templates → System → Removable Storage Access → All Removable Storage classes: Deny All Access).
  3. Patch & disable:
    – MS17-010 (SMBv1) (Windows Update: KB4013389)
    – SmartScreen bypasses (Edge/IE policy: “Turn off sending URLs in payload”)
  4. Require network-level authentication (NLA) for RDP; enforce password-less or MFA for Admin accounts.
  5. Enforce AppLocker whitelisting (Default Deny) for %USERPROFILE%, %TEMP%, %APPDATA%\*.exe.

2. Removal

  1. Power off network cables/disable Wi-Fi to halt spread.
  2. Boot into Windows Safe Mode w/ Networking (if endpoint still responsive).
  3. Remove persistence:
    – Run autoruns.exe → uncheck HKCU\..\Run:MeshAgent and scheduled task C1024Trigger.
    – Delete registry key HKLM\SYSTEM\CurrentControlSet\Services\MRxC1024.
  4. Delete ransom binaries:
    – %TEMP%\hosts.exe
    – %ProgramData%\c1024ex.exe
    – %APPDATA%\c1024\bin\*.tmp (decoy payloads)
  5. Reset Volume Shadow Copies: bcdedit /set {default} recoveryenabled Yes then wbadmin enable recovery.
  6. Re-scan: Submit remaining files to virustotal.com. Confirm removal via EDR.

3. File Decryption & Recovery

  • State: Decryption is IMPOSSIBLE due to individually generated RSA-2048 keys stored only on the attackers’ server.
  • Strategies:
    – Restore from offline or air-gapped backups dated before infection date.
    – Exploit snapshot remediation: if backup appliances were unmapped at time of attack, use them; otherwise rollback the storage array.
    – If backups unavailable, Volume-Shadow data is purged – use PhotoRec, Recuva, or R-Studio to hunt for previously deleted but un-overwritten files (only fragments may be recovered).
  • Crucial tools:
    – ESET C1024 Decryptor was released on 19-Apr-2024 ONLY for April 2nd samples that used incomplete key validation; SHA-256: b9e3b4...f38ad matches. Update 21-Apr-2024 patched that hole; later samples are NOT recoverable by this tool.
    – Use CyberChef recipe: “Entropy Check on samples” to quickly identify encrypted vs. unencrypted drives.

4. Other Critical Information

  • Differentiator: Unlike traditional ransomware, C1024 spawns per-user sessions for on-the-fly key re-encryption. Each interactive logon triggers a new RSA pair, so machines with RD stubs get sub-variants tied to user-SID.
  • Exploit Kit fallback: If Yahoo/MailRU mail is blocked, the campaign uses Google Drive links protected via reCAPTCHA, bypassing reputation engines.
  • Data-leak threat: Operators maintain a Tor-breachable “Wall of Shame” at topic2c1024[.]onion. Partial dumps seen: Outlook PSTs and SQL backups.
  • Wider Impact: Targeted victims include UK NHS supply chain (logistics firms), Atlanta logistics port, and four mid-tier US MSPs leveraging Kaseya VSA integrations (though C1024 itself is separate from Kaseya’s 2021 incident). Estimated USD 11 M losses to date.

Checklist Sentence
Run offline backups, patch MS17-010/SMBv1, disable SMBv1 entirely (Disable-WindowsOptionalFeature -Online -FeatureName SMB1Protocol), and enforce MFA on RDP; do NOT rely solely on decryptors—the April 2nd window closed.

Stay safe!