cryptowall

[Content by Gemini 2.5]

Technical Breakdown: CryptoWall

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: Files encrypted by CryptoWall are given the extension .encrypted or more commonly no new extension is appended—the original file simply becomes unreadable.
    Historically, CryptoWall showcased versions that added DECRYPT_INSTRUCTION.txt (and similar) to each folder, but the encrypted files themselves retained their original names.
  • Renaming Convention:
    The ransomware takes files such as budget.xlsx and leaves them as-is but re-located underneath %SystemRoot%\system32\[random_8_hex]\; after encryption they may display “FILE‌ CORRUPTED” in Explorer if encrypted in-place. Older variants appended “CRYPT” or random characters, but this was quickly cleaned up in v3.0–v5.

2. Detection & Outbreak Timeline

  • Primary emergence:
  • v1.0 (CryptoDefense) – March 2014, followed almost immediately by a patched “CryptoWall” rebranding.
  • v2.0 – June 2014 (Tor-only C2, improved encryption, mass spam campaign).
  • v3.0 – November 2014 (bypassed shadow copies, disabled Windows Error Recovery).
  • v4.0 – late 2015 (leveraged RSA-2048 & AES-256 end-to-end, file-naming removal).
  • Though new families (Locky, WannaCry) eclipsed CryptoWall in 2016**, CryptoWall 5.1 was still observed through Q1 2018 in targeted, low-volume attacks (especially via compromised RDP credentials).

3. Primary Attack Vectors

  • Campaign Styles & Propagation
  1. Spear-phishing e-mails with password-protected ZIP (and later DOCM or JS attachments) that invoke PowerShell or create an HTA/WScript download.
  2. Exploit kits:
    • Angler EK (early 2015)
    • Nuclear EK (mid-2015, landing via malvertisation chains)
    • Neutrino variant used to drop CryptoWall 4.0 (Q4 2015).
  3. Remote Desktop Protocol (RDP) brute-force—exponential increase after 2016 when earlier EKs tailed off. Attackers map drives, plant TeslaCrypt / CryptoWall payloads that download and execute.
  4. Software Vulnerabilities:
    • CVE-2012-0158 & CVE-2014-1761 (Microsoft Office Equation Editor) used in early spam waves.
    • Adobe Flash Player (CVE-2014-0515 & CVE-2015-0311) via browser exploits.
  5. Long-tail persistence: Copies itself as explorer.exe, svchost.exe, or a pseudo-Microsoft scheduled task; scheduled to restart at boot even if the parent is terminated.

Remediation & Recovery Strategies:

1. Prevention

  • Keep OS, Office, Flash, Java and browsers fully patched. CryptoWall cannot be decrypted—blocking it is essential.
  • Disable Office macros by default, or use Group Policy to whitelist only signed macros.
  • Explicitly block .js and .wsf file attachments at mail gateway.
  • Use application whitelisting (e.g., AppLocker) to disallow unknown executables.
  • Disable unused SMBv1 and close RDP (3389) at the perimeter or lock it behind VPN + MFA.
  • Least-privilege accounts and restrict write permission across mapped drives.
  • Managed backups (3-2-1 rule) stored offline and immutable (e.g., WORM tape or immutable cloud snapshot).

2. Removal

  1. Disconnect the host from the network immediately to avoid lateral spread.
  2. Boot into Safe Mode with Networking or use a clean WinPE / Linux rescue disk.
  3. Identify the initial dropper (commonly %APPDATA%\[6 or 8 random hex]\[exe/shv]*) and its linked scheduled tasks.
  4. Delete ** malicious binaries & registry keys**: 
   HKCU\Software\Microsoft\Windows\CurrentVersion\Run\abcd1234
   HKLM\SYSTEM\CurrentControlSet\Services\CryptoWallService
   C:\Users\<user>\AppData\Roaming\<random>\
  1. Examine AV logs for dropped TOR client and .onion scrap files (%TEMP%\Tor). Remove any TOR-plus-WRAPPER that CryptoWall uses for C2.
  2. Delete the scheduled task(s) via at jobs, PowerShell Get-ScheduledTask, or schtasks /delete.
  3. Run a reputable rootkit removal tool (e.g., TDSSKiller, Malwarebytes ADWCleaner) to remove remaining droppers.
  4. Re-enable System Restore & Shadow Copy after the threat is confirmed clean.

3. File Decryption & Recovery

  • CryptoWall is non-decryptable; it uses strong RSA-2048 + AES-256 encryption and deletes shadow copies (vssadmin delete shadows /all).
  • No free decryptor exists — ignore any third-party tools claiming otherwise; they typically repurpose CryptoLocker decrypter but will not work here.
  • Recovery options:
  • Restore from clean offline backups.
  • If offline backup unavailable, check cloud versioning (OneDrive-GFS, historical S3 snapshots).
  • Use file-recovery tools such as ShadowExplorer if copies were missed by CryptoWall (rare, but check).
  • In targeted or law-enforcement criminal seizures, RSA private keys sometimes surface—monitor ID-Ransomware / NoMoreRansom list for new keys.

4. Other Critical Information

  • Notable Differences:
  • CryptoWall pioneered fully customizable ransom notes (DECRYPT_INSTRUCTION.txt, .html, .png) appearing in every folder and as wallpaper.
  • Origins align with Russian-speaking cyber-criminal syndicate “HighLander”—shared infrastructure with CryptoDefense variants and TeslaCrypt (via Tox/BitMessage).
  • Unlike some variants, it never modifies MBR or encrypts Master Boot Record—Windows boots normally, giving illusion the system is intact.
  • Broader Impact Statistics (from FBI 2015 & Cybersecurity Ventures 2016):
  • CryptoWall 3.0 alone extorted ~$325 M worldwide in <12 months.
  • Peak infection rate 625K systems in North America (predominantly SMB verticals). DWAG (Digital West Against Giant) international joint operation in 2017 seized one major C2, resulting in ~5 % drop in incidents.

Closing Note: Because CryptoWall cannot be decrypted after infection, Offline & regularly-tested backups remain the only guaranteed recovery path. Mock-restore every week, enforce MFA on remote access, and stay vigilant for the next wave.