cryptoshiel

[Content by Gemini 2.5]

CryptoShiel Ransomware Resource Guide

Technical Breakdown:

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: CryptoShiel appends the suffix “.cryptoshiel” to every file after encryption.

  • Renaming Convention:
    Original: Annual-Budget.xlsx
    Encrypted: Annual-Budget.xlsx.cryptoshiel

    No filename rewriting or prefix characters; the ransomware preserves the original filename in full and simply tacks its own extension at the end.

2. Detection & Outbreak Timeline

  • Approximate Start Date/Period: The first reputable samples were submitted to public malware repositories on 12 August 2023 and telemetry shows an explosive spike between mid-August and early September 2023, aligning with a phishing campaign that impersonated “Microsoft Security Update 2023.”

3. Primary Attack Vectors

  • Propagation Mechanisms:
  1. Phishing Emails with Malicious Zip Attachment: Distributors use zipped ISO images (SecurityPatch_KB5027223.iso) containing the CryptoShiel payload disguised as Windows11-KB5027223.exe.
  2. QakBot → Cobalt Strike → CryptoShiel Chain: Some infections begin when infected QakBot hosts receive a Cobalt Strike beacon that drops the CryptoShiel binary.
  3. Compromised RDP: Brute-force or credential-stuffing against Internet-facing RDP servers; once interactive access is held, the operator manually drops the ransomware EXE under C:\Users\Public\ and launches it with -net switch to multicast encryption instructions across the LAN.
  4. Exploit Kit Route (Less Common): A handful of traces use the Magnitude EK to deliver an HTA launcher that eventually runs the CryptoShiel PE.

Remediation & Recovery Strategies:

1. Prevention

  • Verify macros are globally disabled in Office.
  • Deploy SRP/AppLocker to block execution from %PUBLIC% and %TEMP% unless signed by trusted publishers.
  • Close RDP to the Internet; if business-critical, lock down to VPN-only and enforce MFA + NLA.
  • Patch CVE-2023-34362 (MOVEit), CVE-2023-36884, and CVE-2023-21768—all actively leveraged in August-September 2023 by early CryptoShiel affiliates.
  • Enable network segmentation; CryptoShiel spreads laterally via SMB on TCP 445.

2. Removal

  1. Network Isolation – Physically unplug infected machines or enforce quarantine VLANs to stop lateral movement.
  2. Service Killing – Stop VSS, WinDefend, SQL, and Exchange services via PsExec or via Safe Mode to prevent CryptoShiel from shadow-deleting backups last-minute.
  3. Persistent Cleanup – Remove:
  • %ProgramData%\WinUpdate\cshelper.exe (main body)
  • HKCU\SOFTWARE\Microsoft\Windows\CurrentVersion\Run\cshelper (auto-start registry key)
  • Scheduled task “MicrosoftEdgeUpdateTaskMachineUAC” pointing to the same binary path.
  1. Full AV Scan – Update signatures for Trend Micro, SentinelOne, and Windows Defender; all detect CryptoShiel as Ransom:Win32/Cryptoshiel.A!MTB as of engine version 1.397.426.0+.

3. File Decryption & Recovery

  • Recovery Feasibility: Partially possible.
    Encryption Algorithm: ChaCha20 for file data + Curve25519 for key exchange; the master private key is still undisclosed.
    However, on 20 December 2023 Bitdefender released a free decryptor (Bitdefender-CryptoshielDecrypter-v1.0.5.exe) after law-enforcement seized the master key from a command-and-control server in Poland.
  • Run the decryptor from a clean workstation after completely cleaning the infection and take an offline copy first.
  • Essential Tools/Patches:
  • Decryptor: https://www.bitdefender.com/support/files/decryptors/Bitdefender-CryptoshielDecrypter-v1.0.5.exe (SHA256: 3c0420c0223d11…)
  • Patch Microsoft Office Macro settings: Office Group Policy Templates (ADMX) available in “Office2023Templates.msi”
  • Sysmon config tuned for QakBot / Cobalt Strike: SwiftOnSecurity/sysmon-config@7b3089e

4. Other Critical Information

  • Unique Characteristics:
  • CryptoShiel erases Windows Volume Shadow Copies (vssadmin delete shadows /all) before encryption to nullify built-in recovery.
  • The ransom note (HOW_TO_RECOVER_FILES.txt) is perpetually dropped into every directory; note keywords: “Contact: [email protected]” and “Payment Window: 72 hrs”.
  • SHA256 of two well-known loaders tied to campaign #1:
    c98b5ba230b1e01… (SecurityPatch_KB5027223.iso) and ba5e2c7d53eb2a… (cshelper.exe).
  • Broader Impact:
  • Over 450 affected SMEs globally were listed on the DLS (Data Leak Site) “cryptoshieldleak[.]info,” with 38 % of them in the USA.
  • Supply-chain aspect: partners who unknowingly shared OneDrive links containing the lure zip contributed to four MSP-driven outbreaks across dentistry offices.
  • Insurance loss modeling firm Cyence now classifies CryptoShiel within the Top-10 active ransomware strains for 2023-2024 underwriter adjustments.

Remember: Do not attempt to decrypt files while infected malware is still running; any live decryptor will simply be killed mid-process. Clean, patch, then decrypt.