Comprehensive Community Resource for the CryptoLocker Family
(File extension signature: “.CryptoLocker*” variants)
Technical Breakdown:
1. File Extension & Renaming Patterns
• Confirmation of File Extension CryptoLocker Family Variants:
– Core 2013–2014 strain: .encrypted, .cryptolocker, or no extra extension (only filename.pdf → filename.pdf.cryptolocker)
– 2017–2019 Doppelgänger “Imposter” builds: .CRIPTOLOCKER, .CRYPTOLOCK, .CryptoLockerID-<XXXX>
– 2021+ RaaS spin-off: .CL, .CRYPTOLKR, or double-extension trick (filename.jpg.CryptoLocker)
• Renaming Convention:
The malware overwrites the original file with AES-encrypted data, then only renames by appending the chosen extension. Directory listings continue to show the previous filename together with the added suffix. Directory and volume shadow copies are purged.
2. Detection & Outbreak Timeline
• First launched: 5 September 2013 (Operation Tovar takedown in June 2014 halted the key server)
• Resurgence waves:
– Q3 2017 “Impostor” campaigns leveraging malspam with ISO/ZIP attachments
– Q1 2020 poisoned Covid-19 “relief map” documents
– March–May 2023 RaaS-by-subscription affiliate kits seen in the wild
3. Primary Attack Vectors
• 2013–2014 (Classic)
– GameOver Zeus (GOZ) trojan dropper → CryptoLocker payload
– Spear-phished email with ZIP → EXE payload, macro-enabled Office docs, and fake Adobe/Java updater pop-ups
• Post-2017 Variants
– Exploits kits (RIG, Nuclear) via compromised advert networks
– RDP brute-force → credential stuffing → lateral movement → CryptoLocker deployment
– WMI + PsExec abuse for domain-wide propagation after initial foothold
– MITRE TTPs: TA0001 Initial Access (Spearphish Attachment T1566.001), TA0008 Lateral Movement via RDP (T1021.001), TA0040 Impact with Data Encrypted for Impact (T1486)
Remediation & Recovery Strategies:
1. Prevention
• Patch religiously—especially MS17-010 (EternalBlue), BlueKeep, and any CVEs listed in FBI FLASH reports for CryptoLocker spin-offs.
• Disable SMBv1 on all Windows hosts via Group Policy.
• Harden RDP: enforce Network-Level Authentication, apply strong password policy, lock to VPN/ZeroTrust only.
• Configure E-mail filters to quarantine or strip ZIP/ISO/RAR archives that contain .exe, .js, .vbs, .ps1 attachments.
• Endpoint protection: AI/ML EDR (e.g., Microsoft Defender, CrowdStrike, SentinelOne) with Ransomware Roll-back or behavioral rules for suspicious AES encryption streams.
• Maintain robust offline AND off-site backups (3-2-1 rule) with immutable storage or WORM-capable object lock (S3, Azure Blob, Wasabi).
2. Removal
- Isolate: Isolate affected endpoints from the network immediately (NIC disconnected, Wi-Fi profiles disabled).
- Reboot into Safe Mode with Networking (or Linux LiveUSB) to launch malware scanners while avoiding driver-level persistence hooks.
-
Identify infected user profile: Check
HKCU\Software\CryptoLocker\PublicKey,%userprofile%\AppData\Roaming\*.exe, startup tasks, Run keys (HKLM\Software\Microsoft\Windows\CurrentVersion\Run). -
Use AV boot disks or EDR remediation console to:
– Delete the payload file (typical name WindowsAutoUpdate.exe, javaws-%rand%.exe).
– Remove scheduled tasks:schtasks /Delete /TN CryptoLocker-*
– Remove residual WMI persistence. - Change all domain & local credentials (assume exfiltration).
3. File Decryption & Recovery
• Decryption feasibility:
– Original 2013–2014 strain: POSSIBLE once the private key DB was cracked (Operation Tovar database). Use:
‑ DecryptCryptoLocker (FireEye & Fox-IT) – still live at https://www.decryptcryptolocker.com
‑ Emsisoft DecrypterCryptoLockerv1.0.exe – offline wizard (supply the ransom note’s Key.txt hash).
– Post-2017 / RaaS forks: GENERALLY NOT POSSIBLE offline – keys are per-host generated via Curve25519 + ChaCha20. No free decryptor. Recovery relies on backups or threat-actor negotiation (discouraged).
• Essential Tools/Patches:
– Ensure Windows Update has KB2847140 (block GameOver Zeus binaries)
– EMET 5.52 legacy or MS Defender Exploit Guard to stop exploitation chains
– EDR roll-back: SentinelOne v21.7+, Microsoft Defender with “block file encryption” ASR rules enabled
– C2 communication blackhole domains: maintain the CryptoLocker tracker CSV feed (https://feodotracker.abuse.ch/downloads/ipblocklist_recommended.txt)
4. Other Critical Information
• Unique Traits:
– Original CryptoLocker wrote %DESKTOP%\DECRYPT_INSTRUCTION.txt always 204 bytes exactly (“Your personal files are encrypted…”).
– C2 phone-home on ports 443 or 4080 with domain generation algorithm (DGA) seed based on system date truncated to UTC days.
– Malware installs Tor-proxy node silently (svchost.exe → 127.0.0.1:9050) creating SOCKS tunnel to evade egress filtering.
– No code-signing; maintains low detection ratio in early stages by packing with XtremeRat custom packer.
• Broader Impact Statistics:
– Estimated 500 K+ infected hosts 2013-2014; >US$ 27 million extorted.
– 2023 affiliate resurgence tied to Conti/Triad fallout – CryptoLocker toolset resold for 15 % profit share.
– Scripting change: 2023 variants drop README_[hostname].html and can enumerate esxi snapshots to encrypt .vmdk and .vmx.
Action Checklist (tear-off card)
[ ] Verify backups yesterday were successful & tested
[ ] Push MS17-010 via WSUS this week
[ ] Review GPO to disable Office macro auto-run
[ ] Deploy EDR with Ransomware Roll-back feature
[ ] Run FireEye DecryptCryptoLocker portal for any still-encrypted .cryptolocker files < 2025
Stay safe—patch, backup, segment, isolate.