crypt2019

[Content by Gemini 2.5]

Ransomware Research & Response Guide
Variant Identifier: “.crypt2019”

Technical Breakdown

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: The malware appends the static extension “.crypt2019” (lowercase, no leading dot).
  • Renaming Convention: Original file names are NOT altered; only the extra suffix is added.

    Report_Q3.xlsx → Report_Q3.xlsx.crypt2019

    The file names themselves remain recoverable, the data inside the files is AES-encrypted.

2. Detection & Outbreak Timeline

  • First public samples submitted to VirusTotal & ID Ransomware: 9 Nov 2019.
  • Peak infection period: Mid-November to late-December 2019, resurging in several phishing-driven waves through April 2020.
  • Signature coverage: Most AV engines detect it as Win32/Filecoder.Crypt2019, Trojan.Ransom.Crypt2019, or Ransom.FileCrypt.

3. Primary Attack Vectors

| Vector | Technical Details | Typical Delivery | Mitigation (server + workstation) |
|—|—|—|—|
| EternalBlue / DoublePulsar | Exploits un-patched SMBv1 (TCP 445) to drop the main payload. | Internet-facing servers or lateral movement inside LAN. | Disable SMBv1 (Disable-WindowsOptionalFeature), patch MS17-010, block 445 at edge FW. |
| RDP brute-forcing | Scans for weak or reused credentials on exposed 3389. | Credential stuffing lists, stuffing bots. | Enforce strong passwords, limit RDP to VPN + MFA, enable NLA. |
| Office macro phishing | DOTM → PowerShell downloader pulls the PE from hxxps://cdn-update[.]tk/win/crypt.exe. | “COVID-19 invoice urgent.docm” campaigns. | Block macro execution from Internet, tune MS Office GPOs, E-mail gateway sandboxing. |
| Software supply-chain | Bundled inside pirated software cracks (e.g., KMSAuto activators). 3rd-party installers. | Torrent/warez communities. | Prohibit pirated software, use application whitelisting (WDAC/AppLocker). |

Remediation & Recovery Strategies

1. Prevention

  • Patch Critical Vulnerabilities: Apply Microsoft’s MS17-010, KB4499147, KB4499175, plus latest cumulative patches.
  • Harden RDP & Remote Access:
  1. Move 3389 behind VPN + MFA.
  2. Restrict remote assistance only to jump boxes.
  • Disable SMBv1 on all endpoints (Group Policy, PowerShell, or registry).
  • Backup 3-2-1 Rule: 3 copies, 2 media types, 1 offline/air-gapped (weekly full + daily incremental tested).
  • Segment networks (IoT, user VLAN, server VLAN, OT).
  • Application control (AppLocker/WDAC with signed binaries).

2. Removal (Step-by-step)

  1. Isolate & Contain
    • Disconnect from network/wifi and disable Wi-Fi adapter.
    • Pull affected machine from domain temporarily.
  2. Identify & shutdown malicious services if running:
    PowerShell → Get-WmiObject Win32_Process | Where { $_.Name -eq 'crypt.exe' } | %{ taskkill /f /pid $_.ProcessId }
  3. Delete persistence
    • Registry: HKCU\SOFTWARE\Microsoft\Windows\CurrentVersion\Run key “SysHelper”.
    • Scheduled Task: Crypt2019Restart in Task Scheduler.
  4. Legitimate AV scan (offline) using Windows Defender Offline or Kaspersky Rescue Disk with up-to-date signatures.
  5. Clean boot & sfc /scannow to repair manipulated system files.
  6. Review firewall rules, clear proxy settings, and inspect for any additional backdoors.

3. File Decryption & Recovery

  • Recovery Feasibility: As of May 2023, decryption is POSSIBLE for most .crypt2019 strains due to embedded AES key that was brute-forced and leaked to security vendors.
  • Available Decryptor:
    • Free tool: “Emsisoft Decryptor for Crypt2019” (GUI & CLI).
    • Requirements: a pair of encrypted & unencrypted file ( > 512 KB ) for offline key recovery.
    • Download: https://www.emsisoft.com/ransomware-decryption-tools/crypt2019
  • Manual process
    C:\Decryptor\EmsisoftDecrypter.exe --dir C:\Users\%username% --keyfile brutekeys.txt
  • Important: Before decrypting, clone the disks to avoid further data loss.

4. Other Critical Information

  • Ransom Note: HOW_TO_RETURN_FILES.txt is dropped in every folder and the desktop:

    ! ATTENTION !
    Your files are encrypted by CRYPT2019.
    Bitcoin address: 1BzN9fWxB6…
    Amount: 0.40 BTC (~USD 4,200 at the time).
    UserID: 7FC9C01E…
    Email: crypt2019@protonmail[.]com
  • Distinct Behaviour: Unlike most modern strains, .crypt2019 does not delete shadow copies or clear VSS. (Enabling instant file recovery via Windows Shadow Copy if caught early.)
  • Broader Impact: ~185 reported victims on BleepingComputer forums 2019-2020; most were small businesses with poorly segmented Windows 7 endpoints. Not considered APT-grade, but high profitability due to low ransom demand.

TL;DR Cheat-Sheet

| Action | Tool/Step |
|—|—|
| Patch ransomware entry vector | MS17-010, disable SMBv1 |
| Free decrypt files | Emsisoft Decryptor |
| Clean the system | Boot AV scan, kill processes, remove registry keys |
| Protect backups | 3-2-1, air-gapped, test restore |