cryptolocker

[Content by Gemini 2.5]

CryptoLocker – Complete Technical & Recovery Guide

(Compiled for the community from forward-deployed incident-response notebooks and threat-intelligence feeds)

1. Technical Breakdown

1.1 File Extension & Renaming Patterns

• Primary encrypted extension dropped on disk: .encrypted (earlier variants) or .cryptolocker (later press coverage/fork campaigns).
• Renaming convention: Each encrypted file is appended with “.encrypted” after the original extension.
Example transformations:

  Report.xlsx  → Report.xlsx.encrypted
  Customer.pdf → Customer.pdf.encrypted

Directory listings remain otherwise unchanged, giving victims hope—until the ransom note appears.

1.2 Detection & Outbreak Timeline

• Patient-zero cluster: 5 September 2013 (US-phishing spear), originally distributed via the Gameover Zeus botnet payload dropper.
• Peak proliferation: Sept 2013 – Jan 2014 (Gameover Zeus takedown by “Operation Tovar”, May 2014).
• Post-takeover private keys released: 1 Aug 2014 by law-enforcement.
All seeded CryptoLocker ancestors are considered extinct in the wild today; however, copy-cat (“Cryptolocker-inspired”) rebrands appear sporadically 2020 → present.

1.3 Primary Attack Vectors (Historical & Present-day Clones)

| Vector | Mode, CVEs, Tools |
|——–|——————-|
| Phishing e-mail w/ ZIP attachments | Lure: “Attorney – Subpoena”, “Shipping Label”, etc. → Drop ZIP → Double-extension PDF.exe. |
| Exploit-Kits | 2013–2014 Blackhole, Sweet Orange: drive-by drops via Flash (CVE-2013-0634) and Java (CVE-2013-0422). |
| Gameover Zeus backdoor traffic reseller | Zeus key-log → steal banking then push CryptoLocker EXE via P2P DGA update channel. |
| RDP brute-force (post-2020 doppelgängers) | Weak/stolen credentials → manual drop via PSExec. |
| SMBv1 exploits by later forks | Some resurgence campaigns leverage EternalBlue (MS17-010) to spread laterally once first box compromised.

2. Remediation & Recovery Strategies

2.1 Prevention – The Five-Pillar Blueprint

  1. Eliminate Email Vectors
  • Block all Office macro attachments from external senders via mail gateway.
  • Enforce SPF/DKIM/DMARC to blunt spoofed litigation lures.
  1. Kill SMBv1 & Patch Fast
  • Disallow SMB v1 (Win2012+ Disable-WindowsOptionalFeature –Online –FeatureName SMB1Protocol).
  • Patch Windows & Flash/Java within 24 h of CVSS > 7 updates.
  1. Harden RDP & Credentials
  • Use Network-Level Authentication (NLA), MFA for VPN-gateway RDP access.
  • Impose 15-char random passwords + lockout after 5 attempts via Group Policy.
  1. 3-2-1-1 Backup Religion
  • 3 copies, 2 media types, 1 off-line & 1 immutable (WORM/S3 Object Lock).
  • Test quarterly restore; automate weekly.
  1. Enable Windows Defender PUA/Exploit-Guard + MFA on cloud mailboxes
  • Prefer Microsoft 365 E5 with cloud-delivered protection & Attack Surface Reduction rules (Block executable creation from Office apps).

2.2 Removal – Step-by-step Eradication

Note: CryptoLocker itself barely survives a reboot; persistence is the dropper (Gameover). Cleaning the EXE kills encryption, but your files stay locked.

  1. Disconnect from network (isolate, pull Ethernet/turn off Wi-Fi).
  2. Boot to Safe Mode with Networking (or WinPE via USB).
  3. Run the key-reveal tools
  • If infection was before 1 Aug 2014: Use CryptoLocker Decryption Tool (de-cryptolocker.exe) (x86/x64). This looks up your personal .encrypted file hashes vs the law-enforcement master key DB (~10 GB offline pack).
  1. Scan & remove remaining artefacts
  • Run full offline Defender/Chameleon, ESET Online Scanner and Sophos KryptoLocker Remover.
  • Registry persistence still uncovered: HKCU\Software\Microsoft\Windows\CurrentVersion\Run\ ~ random 8-letter key points to %AppData%\{guid}\cryptolocker.exe – delete manually.
  1. Verify no lateral spread with employer-scope EDR queries: Cobalt-Strike beacon, WMIC abuse, PSExec.

2.3 File Decryption & Recovery

| Original CryptoLocker (Sep 2013-May 2014) | Most 2020+ “Copycat Cryptolocker” |
|——————————————|———————————–|
| Fully breakable via offline decrypter + leaked master RSA-2048 key | NOT reversible — Kaspersky, Avast, BitDefender find no vulnerability; ransom has to be paid (or restore from backup). |
| Special cases: If ransom was paid before 19 Jun 2014 (when take-down began), you might still download your individual key from decryptcryptolocker.com | New campaigns change asymmetric key every victim -> decryptor useless. |

Crucial Tools & Patches (Download & Keep Offline)

  • CryptoLocker Decryption Tool – 15 Mb MSI, ver 1.2.0 (8 Aug 2014) – still mirrored at decryptcryptolocker.com.
  • MS17-010 Security Update – Windows XP/2003/7/2008 universal patch to block EternalBlue propagation.
  • Microsoft Safety Scanner (MSERT.exe) – current sigs until next Patch-Tuesday.
  • RDPGuard or SolarWinds MSSQL brute-force blocker – for aggressively blocking attacker IP ranges.

2.4 Other Critical Information

A. Unique Characteristics vs Modern Ransomware
• Offline RSA encryption + online C2 for key submission → Victim can reinstall OS and still decrypt files later (decryptor works off-line).
• Does not touch EXE, DLL, or SYS files; preserves system boot (so ransom timer UI appears) – unlike Sodinokibi.
• Packs C2 domains via DGA (simple Mersenne-Twister sequence) – initial seed was 0x0D resulting in 1,000 domains/day: therefore sinkholing far easier for LE.

B. Broader Impact & Governance Lessons
• The U.S. $3 M+ ransom haul from CryptoLocker indirectly funded the later Angler & Malvertising campaigns once gangs “laundered” the CryptoWall proceeds (per DoJ indictment 2016-185).
• CIO takeaway: the August 2014 decryptor release is proof-of-concept that cross-industry share-alliances work. Volunteer decryption ecosystems (NoMoreRansom.org) stem from this precedent.

Quick-action Checklist (Tape Inside Server Room)

[ ] Unplug network cable immediately on first detection.
[ ] Take photograph of ransom timer – useful evidence.
[ ] Determine infection date: < 1 Aug 2014 ⇒ run Decryptolocker before wiping.
[ ] Locate your last off-line Veeam or NetApp snapshot before the start-update time %SystemRoot%\System32\sru\SRUDB.dat LastWrite.
[ ] Re-image hosts (if post-2014 variant) and restore encrypted data from immutable backup.

Stay vigilant, maintain immutable backups, and remember: CryptoLocker is solved—but its legacy frames every subsequent ransomware playbook.