cryptomix

[Content by Gemini 2.5]

Technical Breakdown:

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: CryptoMix continues to use a variety of extensions based on the campaign wave. Common observed suffixes include
    – .cryptoshield, .EXTE, .ZERO, .arena, .work, .harm, and more recently randomized 5-7 character strings such as .VERR0.
    – Do not assume only one extension; additional campaign releases can switch the final suffix or combine it with a numeric identifier (e.g., .srvlogo33).
  • Renaming Convention:
  1. Original file name remains intact—no visible truncation or scrambling.
  2. A static e-mail address (example: [email protected]) is appended before the extension.
  3. Pattern ⇒ [original file name] + [+] + [campaign e-mail] + [.] + [wave-specific extension]
  4. Thus a file budget2023.xlsx becomes
    [email protected]
    or on newer builds
    [email protected]

2. Detection & Outbreak Timeline

  • Approximate Start Date/Period:
    – First appearance: Early March 2016 under the original “CryptoMix” label.
    – Major waves followed almost on 3-month cadence:
    April 2017 – CryptoShield 1.0
    May 2017 – CryptoShield 2.0
    September 2017 – CryptoShield 3.0
    February 2018 – “.arena” wave
    Q4 2018 – Increasingly random extensions and updated propagation module.
    – Still actively circulating via new variants as of 2024, with C2 infrastructure periodically rotated to evade blacklists.

3. Primary Attack Vectors

  • Propagation Mechanisms:
  1. RDP brute-force & credential stuffing. Attackers scan TCP/3389, break weak passwords, then manually deploy the payload.
  2. Exploit kits (particularly RIG-EK, and more recently Fallout EK) pushing CryptoMix payloads directly from malicious ads.
  3. EternalBlue/SMBv1 exploits (MS17-010) leveraged for lateral movement once the attacker establishes a foothold.
  4. Phishing e-mails containing weaponized .zip or .7z archives: inside is either an obfuscated .js/.wsf/script that downloads the dropper, or a trojanized document activating macros.
  5. Compromised software-updater utilities (older CCleaner 5.33 supply-chain incident served a CryptoMix dropper in 2017).
  6. Illegal KMS activators and “cracks” distributed via warez forums and YouTube comments.

Remediation & Recovery Strategies:

1. Prevention

  • Apply all Windows patches—especially MS17-010, KB4499164, KB4499175, and every cumulative update released afterward.
  • Disable SMBv1 protocol company-wide: via GPO or registry: sc.exe config lanmanworkstation depend= bowser/mrxsmb20/nsi and sc.exe config lanmanserver depend= srv2.
  • Harden Remote Desktop:
    – Block TCP/3389 at the perimeter or force it behind a VPN.
    – Enforce Network Level Authentication (NLA), account lock-out after 5 attempts, strong 12+ character passwords.
  • Mail gateway hardening: Drop or quarantine .js, .jse, .wsf, .vbe, and password-protected .zip attachments by default.
  • Endpoint controls:
    – Maintain up-to-date EDR/AV signatures with cloud-delivered protection enabled.
    – Deploy AppLocker or Windows Defender Application Control to disallow unsigned binaries from %TEMP%.
  • Backups: Maintain air-gapped, offline, and immutable backups. Test monthly restore for completeness and integrity.

2. Removal

  1. Immediately isolate the infected system from the network (disable NIC/Wi-Fi).
  2. Boot into Safe Mode with Networking.
  3. Identify and terminate the active process (usually a randomly-named .exe under %APPDATA%\Roaming\[8-random-chars]\).
  4. Search and delete:
    – Scheduled Task: syshelper (variants), using schtasks /Delete /TN “syshelper” /F.
    – Registry keys: HKCU\Software\Microsoft\Windows\CurrentVersion\Run and identical key under HKLM.
  5. Remove persistence via WMI or RunOnce if present.
  6. Run Windows Defender Offline scan or Malwarebytes Anti-Ransomware Rescue Mode.
  7. Change all local and domain credentials post-eradication; attackers frequently install credential-scraping tools such as Mimikatz alongside the ransomware.

3. File Decryption & Recovery

  • Recovery Feasibility: Since CryptoMix 2.0 (appearing late 2016), the threat actors switched to RSA-2048/AES-256 in CBC mode with keys generated and kept offline; free public decrypter does not presently exist.

  • No known flaw: Encrypted blocks are distinct per file and salt, invalidating previous volume-shadow copy tricks used by earlier families.

  • Mitigation possibilities:
    – Offline backup restore remains the only method proven to yield 100 % file recovery.
    – If Volume Shadow Copy Service (VSS) was not wiped, you can attempt vssadmin list shadows and shadow-copy recovery via Shadow Explorer. CryptoMix variants try to vssadmin delete shadows /all; success rate is low if the variant reached full maturity.
    – Third-party data-recovery firms may rebuild some files from slack space if AES-256 CBC re-encryption was not fully completed before the process was interrupted. Success is marginal and very expensive.

  • Essential Tools/Patches:
    – Microsoft patches: KB4013389, KB4012598, KB2919355.
    – Baseline scanner: Kaspersky Virus Removal Tool, ESET Online Scanner.
    – Decrypter: Currently None; beware of scam sites claiming to sell a CryptoMix decryptor.

4. Other Critical Information

  • Unique Characteristics:
    – E-mail pattern (indicator of a subsequent strain) helps identify the wave.
    – CryptoMix drops a ransom note named _HELP_INSTRUCTION.TXT, _HELP_HELP_HELP.TXT, or (DECRYPT)_[extension].TXT in every encrypted folder and localizes the message based on system language (EN, DE, RU, CN).
    – Network aware: Will enumerate mapped drives, DFS, and accessible network shares including SAMBA via SMBv1/SMBv2.
    – Attribution: Linked to the “GandCrab/Revil affiliate group”; some decrypt keys discovered in 2019 leaks hint shared infrastructure.
  • Broader Impact:
    – In US healthcare environments (2017–2018), CryptoMix led to downtime costing millions; HIPAA settlements recorded > USD 1.5 M per incident.
    – City of Leeds, AL (2018) public safety dispatch crippled, forcing manual 9-1-1 routing.
    – Manufacturing & SMB sectors still report new infections via exposed RDP documented in VERIS and ICS-CERT incident tracking.

Immediate Action Checklist

  1. Confirm extension matches CryptoMix pattern.
  2. Quarantine affected unit(s), log everything.
  3. Do NOT reboot the machine left untouched—police evidence forensics if required.
  4. Restore from verified, offline, password-protected backup.
  5. Patch, refirewall, and roll out GPO hardening settings.
  6. Raise staff awareness—CryptoMix continues because phishing and RDP remain the weakest links.