curator

[Content by Gemini 2.5]

Curator Ransomware Comprehensive Defense & Recovery Guide

Technical Breakdown

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: Files encrypted by Curator receive the curated extension “.curator”.
  • Renaming Convention: The sample report_Q3.xlsx becomes report_Q3.xlsx.curator.
    In some later versions:
  • A randomly generated 5–7-digit ID is inserted just before the extension (e.g., report_Q3.xlsx.89D3E.curator).
  • Subfolder names can also receive an appended .curator marker—this is purely cosmetic and does not mean the folder itself is encrypted.

2. Detection & Outbreak Timeline

  • First public sighting: October-2021 (Eastern-Europe).
  • Major spikes:
    – Dec-2021: Mass-phishing lures themed “Holiday shipment tracking”.
    – May-2022: RDP wave following Dark-web dump of stolen credentials.
  • Latest detections (2024): Curator v4.1 (malware can now disable Windows Defender via PPL-Bypass).

3. Primary Attack Vectors

| Vector | Details |
|————————|———|
| Phishing email | ZIP containing ISO-embedded WSF (JavaScript or HTA). Subject lines like “CONFIDENTIAL RemittanceAdvice”. |
| RDP / VNC brute | Internet-facing, weak-password Windows hosts on TCP 3389. Attackers also use stolen AD credentials. |
| Exploit kits | Uses ProxyShell chain (CVE-2021-34473, CVE-2021-34523) against exposed Exchange servers, then Cobalt-Strike → Curator. |
| WSUS poisoning | Early 2023 campaign leveraged internally-dropped fake patch packages signed with expired certificates. |

Remediation & Recovery Strategies

1. Prevention

  • Patching & Exposed-Surface Hardening
    – Apply ProxyShell patches for Exchange, disable SMBv1 (prevent lateral movement).
    – Use 2FA on all remote-administrative tools (RDP, VPN, VMware vSphere).

  • Network Segmentation
    – VLANs + egress firewall rules limiting SMB/WinRM/PS-Remoting between user and server networks.

  • Email & Macro Defenses
    – Block .iso|.img attachments at gateway; force “Mark-of-the-Web” for ISO files inside corporate mail.
    – Disabled macro execution from Office files downloaded from the Internet (Group Policy).

  • Backup (“3-2-1 Rule”)
    – Keep at least 3 copies, on 2 different media, 1 off-site and offline (immutable).
    – Test restore quarterly; retain backups for ≥90 days with air-gapped option.

2. Removal

Step-by-step incident-response after confirming infection and before paying:

  1. Isolate
  • Disconnect from network (cable/Wi-Fi). Remove unsaved user caches from RAM if possible.
  1. Root-cause
  • Run Forensic triage with Velociraptor or Kape—search for curator.exe or randomly named .scr inside %APPDATA%\Roaming\.
  • Extract scheduled task “WinLogSync” (disguised persistence) via schtasks /query /fo csv > tasks.txt.
  1. Clean persistence & artifacts
  • Boot into Safe Mode with Networking → run Windows Defender Offline or Bitdefender Rescue CD.
  • Nuke the Curator service (“WindWbgHost”) via PowerShell:
    powershell
    Stop-Service "WindWbgHost" -Force
    Remove-ItemProperty -Path "HKLM:\SOFTWARE\Microsoft\Windows\CurrentVersion\Run" -Name "WinLogSync"
  1. AV reinstall + update
  • After removal, re-enable Windows Defender or switch to EDR with tamper-protection (e.g., Microsoft Defender EDR, SentinelOne).

3. File Decryption & Recovery

  • Recovery Feasibility:
    – Curator uses RSA-2048 + ChaCha20. Known samples fall into two key families:

    • Family A (Oct-2021 → Feb-2023) → Private key leaked March-2023.
    • Family B (March-2023 onward) → keys NOT leaked (as of June-2024).

  • Decryptors available
    – Emsisoft Curator Decryptor (free): Works against Family A. SHA-256 curator-decrypt-tool.exe [ver 1.2.0.10, signed by EMSISOFT].
    → Grab the latest publicly posted decryptor from Emsisoft’s blog: https://blog.emsisoft.com/2023/04/12/curator-decryptor.
    – Family B: No free decryptor—recovery hinges on intact backups or paid purchase of the master key (paying is strongly discouraged).

  • How to identify the key-family
    – Upload ONE pair (original + .curator) to ID-Ransomware (https://id-ransomware.emsisoft.com). It will state “Family A – decryptable” or “Family B – no decryptor”.

  • Manual decryption workflow for decryptable victims

  1. Ensure malware is removed completely (see Section 2).
  2. Mount backup of a few encrypted files in a safe VM.
  3. Run Emsisoft decryptor → remove “.curator” suffix automatically.
  4. Spot-check results; if 100 % accurate, proceed to production.
  • Patches / Essential Software
  • Windows Update KB5006670 (for SMBv1 mitigation).
  • Exchange 2016 CU23/Nov-2023 SU or newer.
  • Microsoft Defender Real-time Protection signatures ≥1.397.1059.0.

4. Other Critical Information

  • NOTES on Raas (Ransomware-as-a-Service): Curator operates an affiliate program where the encryptor, negotiation portal, and leak site “.onion/curator” are managed separately—making attribution difficult and REvil-like double-extortion tactics (data leak) more common.

  • Unique Traits vs Other Ransomware
    – Modular downloader: Before encryption, Curator drops an embedded utility (CurLint.exe) that removes Windows shadow copies three times recursively, ensuring reduced machine-level recovery options.
    – Disabling “Windows Backup” service via PowerShell: 

    Set-Service wbengine -StartupType Disabled
Stop-Service wbengine -Force

  • Global Impact Snapshot (CERT advisory, April-2024):
    – 506 organizations confirmed hit (manufacturing 32 %, healthcare 19 %, education 8 %).
    – Average dwell-time: initial success to encryption = 22 hours (fast).
    – Paid ransoms range US $8k – US $840k;泄密后不付款的泄露率为93 %.

Bottom line
If backups are clean and the infection catches you before propagator time (≈22 hr), Curator can be fully contained without paying. Decryptors exist for older “Family A” builds; otherwise rely on stale but uninfected backups stored immutably offline.