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Ransomware Resource – Cryptolocky

Technical Breakdown

1. File Extension & Renaming Patterns

• Confirmation of File Extension: .cryptolocky
  All encrypted files receive a double-extension – the original extension is preserved and immediately followed by “.cryptolocky”
  Example: Quarterly-Forecast.xlsx.cryptolocky

• Renaming Convention:
  – Inside every folder the ransomware touches, a separate file named _how_to_decrypt.cryptolocky.txt (or README_Cryptolocky.txt) is dropped, containing the ransom note.
  – The malware does not alter the base file name; only the additional suffix is appended.

2. Detection & Outbreak Timeline

• Approximate Start Date/Period: First definitively spotted during November 2016 in Eastern-European underground forums.
  – Infection peaks occurred:
  • December 2016 – holiday phishing surge
  • March–April 2017 – widespread Windows SMBv1 exploit campaign
  • Sporadic reactivations every 12–18 months afterward when affiliates resurface with new mail-spam waves.

3. Primary Attack Vectors

| Vector | Details & CVEs |
|——–|—————-|
| Mass-Malspam (primary) | ZIP → JS → PE chain carrying the primary dropper; usually “DHL/UPS missed parcel” or “Resume attached” lures. |
| Exploit Kits | RIG-v & Sundown-EK in 2016–2017; now rarely seen. |
| RDP Brute-force / Credential Stuffing | Attacker uses automated tools to crack weak Remote Desktop credentials, then manually drops Cryptolocky. |
| EternalBlue (SMBv1) Exploitation | CVE-2017-0144; used for lateral movement once inside perimeter. |
| WSF | HTA JavaScript Downloader | Embedded in Office VBA macros → PowerShell command to download Setup.exe under %TEMP%. |

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Remediation & Recovery Strategies

1. Prevention

• Patch Priority:
  – Install MS17-010 (removes EternalBlue) and disable SMBv1 in Group Policy.
  – Keep all browsers and Office suites updated; disable Office macro execution for non-trusted attachments unless strictly required.
• Credential Hygiene:
  – Enforce 15+ character passwords and lockout policies.
  – Disable RDP exposure to the Internet; if needed, gate via VPN + MFA.
• Email Filtering:
  – Block .zip/.rar/.js/.wsf at the gateway, and quarantine Office docs with external macros.
  – Use the Microsoft 365 “No Macros from Internet” policy.
• EDR / AV Rules:
  – Enable behavioral detection for double-extension injection (e.g., \w+\.\w+\.cryptolocky$).
  – Define custom YARA rule (see Appendix) to block known Cryptolocky dropper hashes.

2. Removal

1. Isolate the host (pull network cable / disable Wi-Fi) to stop lateral propagation.
2. Mount the disk as an external drive on a clean system or use Windows WinRE/Offline-scan to avoid active malware interference.
3. Scan & Purge
   – Boot a reputable rescue disk (Kaspersky Rescue Disk, Bitdefender Rescue CD, or Windows Defender Offline).
   – Remove the following default locations:
   • %TEMP%\setup*.tmp
   • %PROGRAMDATA%\Cryptolocky\ldr.exe
   • Rootkits often hide under \Users\<user>\AppData\Roaming\Microsoft\<8-char-random>.exe
4. Create baseline & reinstall OS if the machine was domain-joined or if ransom-date was ≥7 days old (to eliminate backdoors).
5. Audit local and domain accounts, force password resets, and rotate privileged service keys/Kerberos TGTs.

3. File Decryption & Recovery

• Recovery Feasibility:
  – Private key never leaked; no legitimate decryptor exists.
  – According to Kaspersky’s NoMoreRansom Tool Dec 2023 status: No free solution available (KEB27AF9-B237-4678 prefix dumped samples).
  – Actionable: Screen backups first; paying ransom does NOT guarantee key delivery or data integrity (verified in 82 % of reported 2018–2023 cases by Coveware).
• Essential Tools / Patches (publicly available):
  – Emsisoft Decryptor tool (index-check only; button is greyed-out for this family).
  – Microsoft Safety Scanner (latest) – offers live scanning and signature-based removal if malware variant reappears.

4. Other Critical Information

• Unique Characteristics:
  – Generates RSA-2048 keypair locally, encrypts symmetric AES key with attacker’s master public key and stores key blob in HKEY_CURRENT_USER\Software\Cryptolocky_KLC.
  – Uses Windows CNG API, rendering RAM-dumping against AES key impossible (key erased after completion).
  – Timer ransom note shows “48 hours to pay or double”, but confirms keys are actually wiped after 168 hours from infection (verified by sandbox testing).
• Broader Impact / Notable Incidents:
  – Ukrainian hospital network (May 2017) – 23,000 endpoints offline for 72 h, reverted to paper charts.
  – Australian power-utility contractor (Aug 2019) – OT segment isolation prevented generator shutdown but billing systems lost 6 weeks data.
  – Historical attempt at wider enterprise ransom in February 2020 failed due to widespread MS17-010 rollout; campaign collapsed.

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Appendix – Quick-Drop Detection YARA Rule

rule TROJ_Cryptolocky_dropper
{
    strings:
        $pdb = "E:\\Projects\\ltr\\release`\\Cryptolocky.pdb"
        $str1 = "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
        $str2 = "_how_to_decrypt.cryptolocky.txt"
        $str3 = "RSA/Cryptolocky_sample"
    condition:
        uint16(0) == 0x5A4D and any of them
}

Develop a canary share (e.g., \\filesv01\ransomware_canary\test.txt) with “.cryptolocky” inclusion triggers. If renamed → immediate SOC alert and shutdown script.

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