crypt-*

[Content by Gemini 2.5]

Malware Report: The “crypt-*” Variant (a.k.a. CryptoMix / CryptFile2)

Technical Breakdown

1. File Extension & Renaming Patterns

  • Confirmation of File Extension:
    Encrypted files receive a new 32-character extension beginning with “crypt-” followed by hexadecimal characters (e.g. .crypt-1A2B3C4D5E6F7890ABCD1234E5F67890, .crypt-0C7E…, etc.). The full extension is 37 bytes long (including the hyphen).

  • Renaming Convention:

  • Original filename remains as-is; only the extension is appended.

  • Files in the same folder will never reuse the same 32-character suffix, so every encrypted object ends with a unique token derived from a key-IV pair.

2. Detection & Outbreak Timeline

  • Approximate Start Date/Period:
    First public samples were captured in late April 2017; the campaign peaked during May–July 2017. Sporadic waves resurface every 6-9 months, often masquerading under new distribution affiliate codes.

3. Primary Attack Vectors

  • Propagation Mechanisms:
  1. Spear-phishing e-mails with .ZIP → .JS → downloader chain.
  2. Malvertising via RIG and Glupteba exploit kits (IE/Silver Flash 0-days prior to Nov 2017).
  3. RDP brute-forcing – guesses weak or reused administrator passwords, then manually drops the payload.
  4. EternalBlue / DoublePulsar leverage for lateral SMBv1 abuse.
  5. Fake browser-update pages (especially Chrome/Firefox pop-ups) offering booby-trapped installers.

Remediation & Recovery Strategies

1. Prevention

  • Patch timely: MS17-010, disable SMBv1, remove Flash/Java if unused.
  • User training: Flag e-mails with dual extensions, unexpected .JS/.WSF/.HTA, and macro-enabled Office files.
  • E-mail filtering: Block .ZIPs containing executables at the gateway.
  • Secure RDP: Move 3389 off TCP/3389, enable Network-Level Authentication, restrict by IP or VPN, enforce complex passwords + MFA.
  • Application whitelisting: Use Windows Defender AppLocker / Microsoft Defender ASR rules.
  • Backups: Follow the 3-2-1 rule (3 copies, 2 media, 1 offline/disconnected).

2. Removal – Step-by-Step Cleanup

  1. Isolate the host – unplug network cable, disable Wi-Fi/Bluetooth (Airplane Mode).
  2. Boot into Safe Mode with Networking (or Windows Defender Offline / WinRE if disk encryption is active).
  3. Run a full-scan disk image (e.g., Windows Defender Antivirus, CrowdStrike, or Kaspersky Rescue Disk).
  4. Remove persistence:
  • %ProgramData%\[random_8].exe (main executable)
  • Run keys: HKCU\Software\Microsoft\Windows\CurrentVersion\Run\[[random_base64]]
  • WMI event consumer (attaches scheduled task—delete with WMI Explorer).
  1. Revoke any newly created local accounts the adversary might have added.
  2. Change all passwords (local services/RDP, Microsoft 365, 3rd-party portals) from a clean device.
  3. Apply latest cumulative update for the OS and reboot normally before decrypting anything.

3. File Decryption & Recovery

| Item | Status & Method |
|——|—————–|
| Decryptable? | No – CryptoMix/CryptFile2 uses RSA-2048 + AES-256 in cipher-block chaining with random IV and decrypting keys are never stored locally. |
| Published decryptor? | No off-line decryptor exists for the 2017+ family. |
| Viable paths: | 1. Restore from validated offline backups.
2. Shadow-copy (VSS) or file-history snapshots if they were not purged.
3. File-recovery utilities (e.g., Photorec, Recuva) to fetch pre-encryption versions on SSDs with delayed TRIM.
4. Law-enforcement operations occasionally seize a command-and-control server and provide keys—keep checking NoMoreRansom.org or ID-Ransomware announcements. |

4. Other Critical Information

  • Differentiating traits:
  • Stores a unique machine GUID in the registry (HKCU\SOFTWARE\{machineGuid}) used to link victims to their keys.
  • Drops ransom notes as _HELP_INSTRUCTION.TXT, _HELP_HELP_HELP_[4_hex_digits].TXT; the note includes an onion-link e-mail portal that requires the 32-character suffix.
  • Prior to encryption, it terminates MSSQL, MySQL, QuickBooks, Outlook, and backup agents via taskkill to unlock database files.
  • Check secondary extortion: Recent affiliates exfiltrate up to 200 MB of data before encrypting (clipboard theft, browser cookies, and desktop screenshots). This means even if you recover files via backups you may still be threatened with “name-and-shame.”
  • Impact footprint:
  • Primarily affected health-care and legal entities in the USA/EU during 2017, but current waves are global and targeting MSP break-ins.
  • Average ransom demand 0.5 BTC–1.5 BTC, yet decryption payment success rate reported as <40 % (many keys never delivered).

Key Takeaway
CryptoMix ([crypt-*]) is not decryptable without the attacker’s private key, making offline backups + resilience procedures (patching, RDP restrictions, MFA) the only reliable defense.