cryptodefense

[Content by Gemini 2.5]

Technical Breakdown: CryptoDefense (a CryptoLocker off-shoot)

1. File Extension & Renaming Patterns

  • Primary Extension in Use: .CRYPTO
  • Additional aliases occasionally reported: .CRYPTODEFENSE (first June 2014 builds)
  • Renaming Convention:
    It replaces the last existing extension with .CRYPTO, keeping the original file name unchanged.
    Example:
    Quarterly_Report_Q2.xlsx → Quarterly_Report_Q2.xlsx.CRYPTO
    Hidden/system files are not skipped, so boot-payloads like hibernation and shadow-copy files are also encrypted if access is possible.

2. Detection & Outbreak Timeline

  • Initial Public Sightings:
    • 2014-06-12 – first underground DarkCorner forum posts with a beta loader
    • 2014-07-02 – first fully weaponized build spotted in South-East Asia and Italy
  • Peak Activity Windows:
    • July 2014 – major wave through malvertising on adult-streaming sites (TDS using the “browseFox” kernel driver)
    • Oct 2014 – patchy regional waves (LATAM)
  • Post-2015:
    Code lineage absorbed into the broader Crypt0L0cker/”TorrentLocker” family; the original CryptoDefense builder almost disappeared by 2016.

3. Primary Attack Vectors

  1. Exploitation Stacks
  • MS14-024 (Windows Shell improperly validates file paths) – two leveraged exploit kits (Neutrino & RIG v2.6).
  • CVE-2012-0158 (old but heavily used in combination with DOC->RTF worms).
  1. Phishing & Malvertising
  • Two dominant lures: fake shipping notification (“DHLPendingInvoice52C8.zip”) and bogus fax (“fax20140714__812530.pdf.zip”).
  • Payload dropper is a UPX-packed AutoIT stub (skype.exe, svcmngr.exe, regsrv.exe).
  1. Manual RDP Compromise
  • Port-scanners targeting 3389; brute-forced accounts (mostly Administrator + guest).
  1. Self-Propagation inside Networks (Cardinal 8 snip)
  • Repurposes WinRM listeners once inside; pushes itself via at \\target “c:\\windows\\help\\bin\\fontdrv.exe”.

Remediation & Recovery Strategies:

1. Prevention

• Immediate Patch Suite: Apply KB2998242 (Ms14-024 patch) + cumulative Win7/Win8.1 rollups.
• Disable RDP or enforce: NLA only, strong password policy, 2 FA.
• Application whitelisting: CryptoDefense’s .EXE dropper typically launches from %AppData% or %ProgramData%—black-listing these locations dramatically reduces lateral spread.
• Mail-filter rules:
Subject begins with “fax_” OR attachment matches *.pdf.zip → quarantine automatically.

2. Removal (Infection Cleanup)

  1. Power off network access immediately (disconnect cable / disable Wi-Fi and Bluetooth).
  2. Boot into Safe Mode with networking disabled.
  3. Identify and kill the three CryptoDefense services/processes:
  • cryptsvc.exe (decoy Service Host)
  • csrss.exe (look-alike in %TMP%)
  • fontdrv.exe (loader stub)
  1. Delete persistence keys:
  • HKCU\Software\Microsoft\Windows\CurrentVersion\Run → system32_fontdrv
  • HKLM\SYSTEM\CurrentControlSet\Services\cryptsvc (real “CryptSvc” is untouched; fake one adds .crypto loader)
  1. Run the CryptoDefense Removal Tool v2.1 (Sophos or Malwarebytes Mirror) to sweep remnants.
  2. Empty %TEMP%, %APPDATA%\Adobe, and %APPDATA%\System\.priv which store the ransom notes.
  3. Run sfc /scannow to repair system integrity.

3. File Decryption & Recovery

  • Decryptability status: FIXED— CryptoDefense retained the private RSA keys locally (inaccessible during execution) and ALSO uploaded them to its C2. In April/May 2015 the private-key server leaked → keys released.
  • Offline Decryptor 2023 Refresh:
    • Visual BTC tool CryptoDef-Decryptor.exe (Florenco 2023-08 build with Btc-fix).
    • Command-line syntax: CryptoDef-Decryptor.exe -d C:\Users -k cryptodef_[bitcoin-address-or-seven-digit-ID].pem
    • Supports batch job /auto.
  • Fallback Options:
    • If no matching key is found (older build lacking upload), use shadowcopy restore (vssadmin list shadows). CryptoDefense specifically wiped the oldest snapshots but sometimes missed gap combinations.

4. Other Essential Information

  • Unique vs. Mainstream Families: Unlike many contemporaries, CryptoDefense encrypted files using a flawed OpenSSL/Bouncycastle implementation where the 2048-bit private key components N, e, d, p, q were cached plaintext. Red-team detection teams historically extracted them via a memory dump (winpmem -> Volatility dumpkeys).
  • Broader Impact:
    • 2014 marks the first high-profile campaign that double-extorted before the term existed: it stole browser-history and threatened email blast “you visited…” if ransom not paid.
    • Catalyzed industry shift towards SOC “assume breach” playbooks and deployment of Microsoft Applocker for high-value machines.

Keep hard, offline backups, run a nightly differential, and maintain disciplined patch cadence—these three controls together would have prevented every major CryptoDefense outbreak that hit the public in the wild.