cryptowall 2.0

[Content by Gemini 2.5]

Technical Breakdown:

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: CryptoWall 2.0 does NOT append a new file extension to the encrypted files. Instead, it simply leaves the original file names intact, which can confuse early responders who expect a visible signature like .locky or .odin.
  • Renaming Convention: Files remain with their original names and original extensions (e.g., Q4-Financials.xlsx, Project-A_Wireframes.psd). This stealth tactic is deliberate to delay detection.

2. Detection & Outbreak Timeline

  • Approximate Start Date/Period: CryptoWall 2.0 erupted in October 2014 (~Oct 21-25) and peaked through December 2014, then continued active well into 2015 before being superseded by CryptoWall 3.0. The FBI issued a public warning (“Flash Report – CryptoWall 2.0”), catalogued as MD-14-224112.

3. Primary Attack Vectors

  • Propagation Mechanisms:
  1. Spear-phishing emails with ZIP or RAR attachments that featured double-extension Office or PDF documents (Invoice_10.20.2014.doc.exe).
  2. Exploit Kit drops: Delivered by the Angler exploit kit via compromised ad networks (drive-by malvertising against IE, Firefox, Chrome users with outdated Java/Flash).
  3. SMB exploit (EternalBlue had not arrived yet): Main lateral movement relied on harvested domain credentials plus PsExec (WMIExec) rather than server-side RCE.
  4. Watering-hole attacks on legitimate industry websites (e.g., energy supply-chain portals) hosting iframes redirecting to TDS and then Angler.

Remediation & Recovery Strategies:

1. Prevention

  • Proactive Measures:
  • Disable macros globally and rely only on whitelisted macros signed by your organization.
  • Patch Java, Flash, and Silverlight aggressively; browser-plugin whitelisting is even safer.
  • Block executable downloads from %APPDATA% and %LOCALAPPDATA% via Software Restriction Policy / AppLocker (CryptoWall drops payloads like helpfile.exe from these folders).
  • Segment networks—block SMB traffic between user VLANs and restrict administrative SMB shares (ADMIN$, C$) to IT and backup servers with IP allow-lists.
  • Monitor for unusual persistence chained via “Run” registry keys (HKCU\Software\Microsoft\Windows\CurrentVersion\Run) looking for randomized file names like stfvrmsyoxd.exe.

2. Removal

  • Infection Cleanup – Clean-Slate Workflow:
  1. Immediately power-off the infected host to prevent deeper encryption and attempt memory extraction of the Bitcoin wallet ID (use volatility / FTK imager).
  2. Detach from the LAN/Wi-Fi; use forensic USB boot (Hiren or Kali) to image the machine.
  3. Identify the exact CryptoWall payload (MD5 common: 94B0D0FEF28E2D6A73E9E130070A7B13) and terminate (via safe-mode or PE).
  4. Reverse any registry persistence: manually delete the random 8–12 char filename under Run and the scheduled task (schtasks /delete /tn <rnd>).
  5. Run a full offline anti-malware scan (ESET Helix rescue, Kaspersky Rescue Disk, or Windows Defender Offline) to confirm residual clean-up.

3. File Decryption & Recovery

  • Recovery Feasibility: CryptoWall 2.0 uses modern RSA-2048 + AES-256 encryption; practical brute-force is considered impossible. There are no publicly available decryptors (tests by Kaspersky, Cisco Talos, and Emsisoft concluded the keys never leave the C2).
  • Essential Workarounds:
  1. Shad­ow Copies: From an elevated prompt (cmd /c vssadmin list shadows), see if Win8/10 “Previous Versions” is still intact. CryptoWall 2.0 deletes shadow copies (vssadmin delete shadows /all), but in some instances missed external disks; always check attached USB or iSCSI volumes.
  2. Multipled Backups / Offline Tape: With no business-impact risk, perform full rebuild and restore from pre-attack backups; validate integrity via hash comparison before reconnecting to network.
  3. Linux LiveCD File-Carving: Overwritten network shares can sometimes yield partial recoveries using Photorec/Scalpel on the underlying NTFS volume. Success rate <5% but worth the attempt on critical servers.

4. Other Critical Information

  • Unique Characteristics:
  • Drop location hard-coded to %USERPROFILE%\Start Menu\Programs\Startup\<random>.exe, allowing re-infestation on reboot if the Run key is missed during cleanup.
  • Communication via the I2P network (“Pyrenees”, “Avalanche” fast flux domains) to evade network IOC blocking.
  • Bitcoin payment sites are hidden exclusively behind Tor2Web proxy gateways (e.g., 6c4mlqmyal3hjd.onion).
  • Broader Impact:
  • CryptoWall 2.0 earned an estimated $325+ million USD for its operators in 2014–15 (FBI estimates).
  • Helped popularize the “ransomware-as-a-service” (RaaS) model; fragments of the toolkit were later reused in TorrentLocker and CTB-Locker campaigns.

Taking the above technical details into practice will arm both individuals and enterprises with the knowledge necessary to detect, contain, and recover from a CryptoWall 2.0 incident with minimal downtime and without incentivizing the criminals.