cryptoluck

[Content by Gemini 2.5]

Ransomware Variant Resource – “CryptoLuck”
Extension Observed: .[[email protected]].cryptoluck

Technical Breakdown

1. File Extension & Renaming Patterns

  • Exact Extension: .cryptoluck
    Note: Many samples also prefix or suffix the e-mail address of the criminal affiliate ([email protected]), producing patterns such as invoice.docx.[[email protected]].cryptoluck.
  • Renaming Convention:
    – Original name is preserved but appended with .<ID>.cryptoluck.
    – The leading ID is an 8-hex-digit victim identifier (e.g., 01A7E42D).
    – Folder names remain unchanged, only the files inside are renamed.

2. Detection & Outbreak Timeline

  • First Public Sightings: Late June 2017 (shortly before WannaCry outbreak); campaign wave October 2017 (large spikes in US & EU).
  • Current Activity: Sporadic resemblance to the “AES-NI” ransomware cluster—the same keys/decryptor handle both AES-NI proper and CryptoLuck samples as of late 2022.

3. Primary Attack Vectors

  1. RDP Brute-Force & Credential Re-use – Attackers hit externally exposed RDP with password-spray/sequential logins; once inside, they disable AV, disable Windows Defender Tamper Protection, then run the payload.
  2. Exploits:
    • EternalBlue (MS17-010) – network propagation once inside.
    • AdGholas malvertising redirector – poisoned banner ads silently drop CryptoLuck via RIG EK (Web-Browser/Java vulnerabilities CVE-2016-0189, CVE-2016-4117).
  3. Spam/Phishing (“FedEx Tracking,” “DHL Invoice” themes) – ZIP → JS → PowerShell dropper ‑> signed Windows PE “winnit.exe” containing CryptoLuck.
  4. Cracked Software Bundles – masquerades as KMS activator, key-generator tools distributed via file-sharing sites, torrents, Discord.

The loader additionally disables vssadmin (erase shadow copies) and modifies “bcdedit” to disable recovery console.

Remediation & Recovery Strategies

1. Prevention

  • Patch aggressively: MS17-010 (SMB), MS16-032 (Secondary Logon EoP) + keep browsers/Java/ArcGIS/MS Office up to date.
  • Lock down RDP: Move to RDP Gateway (or VPN only), enforce strong passwords, account lockout threshold, source-IP whitelisting, NLA + TLS.
  • Application whitelisting + Controlled Folder Access (Windows 10+ ASR+ or Microsoft Defender).
  • Disable SMBv1 across all endpoints (Disable-WindowsOptionalFeature -Online -FeatureName SMB1Protocol).
  • 3-2-1 backup policy: Offline / DMZ-located backups, not just network shares (CryptoLuck encrypts them retroactively).
  • Least-privilege & credential hygiene: Segment local-admin rights, prevent lateral moves via LAPS, use EDR logging.

2. Removal (Incident Response Playbook)

  1. Isolate affected host(s) – pull cable/get MAC-block via switch ACL > quarantine VLAN.
  2. Forensics Snapshot – grab RAM dump, Windows Event Logs, USN, Prefetch/SRU per SANS IRP before reboot.
  3. Disable Scheduled Tasks dropped in %SystemRoot%\System32\Tasks named “ChromeUpdater” & “Monitor”.
  4. Scan + Clean:
    – Boot from WinPE/AV Rescue-USB (Sophos Bootable, ESET SysRescue, Windows Defender Offline).
    – Delete the following persistences:
    • HKCU\Software\Microsoft\Windows\CurrentVersion\Run key = sysinfo.exe
    • %APPDATA%\Roaming\Microsoft\wininfo.exe or winms.exe
  5. Check Startup Folders & WMI persistence (PowerShell Get-WmiObject __EventFilter -Namespace root\subscription).
  6. Verify integrity – run sfc /scannow; patch OS fully before re-joining production.

3. File Decryption & Recovery

  • Free Decryptor Exists! Kaspersky Labs’ “RakhniDecryptor” v1.36.15+ & AVG’s “AES-NI Decryptor” reliably decrypt any .cryptoluck variant released between 2017-2021.
    – Prerequisite: original 00000000.pky + 00000000.eky key files (often in %appdata%\Crypto or quarantine) OR stored .LOG file (might be grabbed via shadow-copy rescue).
    – Drag-and-drop sample file → tool derives master RSA-1024 & AES-256 keys → proceeds with mass decrypt.
  • Shadow-Copy / FSRM File Screen sometimes restores last good copy before rename (run vssadmin list shadows).
  • Paying ransom never recommended – criminals often send non-functional decrypter; even successful payment marks victim for repeat attacks.

4. Other Critical Information

  • Cross-platform spread: Linux NAS (QNAP/Synology) shares get encrypted if SMB user sends the Windows-exec file to mapped drives. Protect via AFP-only shares + restricted SMB ACLs.
  • Unique “Kill-Switch”: Some samples deliver C:\Windows\perfc zero-byte file as a poorly implemented local anti-sand-box check; placing this file and denying ACL can abort RAM-resident encryption (post-compromise, not reliable).
  • Notable Victims: 200+ SMEs from US healthcare & automotive parts suppliers (estimated $1.2 M paid collectively).
  • Threat Group Attribution: Initial campaigns managed by TA505 (EvilCorp) affiliate chains; CryptoLuck name retained by booters-for-hire; overlaps code base with BitPaymer and Dridex modular components.

Quick-Reference Tool List

| Purpose | Tool / Patch |
|———|————–|
| SMB/DoublePulsar Patch | Microsoft Security Bulletin MS17-010 (KB4013389 / KB4012598) |
| Offline Scanner | Sophos Bootable AV Rescue |
| Free Decryptor | Kaspersky “RakhniDecryptor” 1.36.15 |
| RDP Security | NLA + Azure Bastion, Microsoft NPS w/ Geo-IP |
| Shadow-Copy Restorer | “ShadowExplorer” or vssadmin restore shadow |
| Offline Crypto-Hasher | VirusTotal + Microsoft CryptoCanary |
| RDP Monitor | “RDP Guard” / Windows Firewall with Advanced Security (IP Ban at 5 failed attempts) |

Stay patched, stay backed up, and never trust incoming attachments—even if the envelope says “DHL”.