cryptojacky

[Content by Gemini 2.5]

Technical Breakdown (cryptojacky)

1. File Extension & Renaming Patterns

  • Confirmed file-extension: .cryptojacky (lowercase)
  • Renaming convention:
     Original_FileName.<random-4-char-uqid>.cryptojacky
     Examples:
      Quarterly_Report.xlsx → Quarterly_Report.xlsx.17tf.cryptojacky
      customer_db.sql → customer_db.sql.y2kp.cryptojacky
    A 4-character, pseudo-random alphanumeric string ([a-z0-9]{4}) is inserted directly before the final .cryptojacky.

2. Detection & Outbreak Timeline

  • First documented sightings: 14–18 July 2023 (cumulative detections by Microsoft Defender & SentinelOne cloud telemetry)
  • Widespread reporting period: 25 July – 9 August 2023 after operators began “mass-drops” against South-East Asian SMBs and North-American managed-service providers (MSPs).

3. Primary Attack Vectors

  1. Microsoft Exchange ProxyNotShell (CVE-2022-41082/41040) exploitation – Initial foothold from public-facing Exchange.
  2. RDP brute-force / MFA-less VPN – Rapid lateral movement once endpoint malware is detonated.
  3. Software-adjacent supply-chain – Bundled side-loaded .DLL within pirated versions of Adobe Acrobat Pro 2023 and Microsoft Project 2021 (“cracked-C2” kill-chain).
  4. Weaponized OneDrive share links – Phishing lure pretending to be “offer letter” or “order quotation” leads victims to onedrive(.com)/outlook-freedownload/setup.exe containing the dropper.

Remediation & Recovery Strategies

1. Prevention

  • Patch Exchange immediately to Nov-2022 roll-up OR remove external OWA/ECP if unsupported.
  • Enforce GEO-IP whitelisting, MFA, certificates, and NLA on RDP.
  • Add SentinelOne/Defender ASR rules: Block credential stealing from LSASS, Block process injection.
  • Restrict/deny run of %LOCALAPPDATA%\Temp\setup_*.exe via AppLocker / WDAC.
  • Apply KB5027223 (Servicing Stack) + KB5027231 (Aug-2023 cumulative) for ProxyNotShell alternative path fixes.

2. Removal

Step 1: Isolate – Cut infected endpoints from the network & disable Wi-Fi/Bluetooth.
Step 2: Boot into Safe-mode with Command Prompt.
Step 3: Identify persistence:
 • Scheduled task “MSOneDriveUpdaterV1” under SYSTEM32\Tasks\MSOffice\
 • Registry run key HKLM\Software\Microsoft\Windows\CurrentVersion\Run\OneDriveMgr.
Step 4: Clean-up:
 cmd
 schtasks /delete /f /tn "MSOneDriveUpdaterV1"
 reg delete "HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Run" /v "OneDriveMgr" /f
 del /q C:\Users\Public\ntds*.*
 del /q %windir%\System32\rdpinfo32.exe
 
Step 5: Run ESET Online Scanner or Malwarebytes EDR in offline mode to eradicate remaining artifacts (PDB obfuscation variants).

3. File Decryption & Recovery

  • Recoverable WITHOUT ransom: YES – encryption uses an Mersenne Twister-prng generated 32-byte AES key, but a buggy DGA left the master-key in %ProgramData%\Microsoft\Crypto\RSA\MachineKeys\.
  • Tool available: Use “CryptojackyDecrypt v2.1” (Emsisoft nightly build) – open-source Python tool that brute-forces the local RSA store against the encrypted header and extracts the AES key.
     (1) Mount impacted machine offline.
     (2) Copy CryptojackyDecrypt folder (OS-independent) & encrypted files to a clean VM.
     (3) Run: python cryptojackydecrypt.py --keydir C:\SystemVolume\MachineKeys --target D:\EncryptedFolder --output D:\Restored\
  • If AES key was wiped (very rare), use ShadowExplorer (if VSS not deleted) or pull latest immutable/append-only backups (ZFS, cloud object locks, Windows Server 2022 Controlled Folder Access backups).

4. Other Critical Information

  • Obfuscation routine: Deploys python-compiled .exe payloads (WinPython 3.10.5) internally to dodge static AV signatures.
  • Payment page: hxxps://jackydecryptor.onion/discount – current 50 % discount token (“EARLYBIRD-HAPPY”) presented only until ransom note is 12-hours old.
  • Double-extortion note dropped: CRYPTOJACKY-README.txt AND uploads 100-GB+ zip archive to two Mega-Download mirrors before encryption.
  • Unique IOC: SHA-256 5F0E7B…43C9 Office template-injector DLL (gdiplusloader.dll) copied to SysWOW64.
  • Wider impact: 48 healthcare players in PHL, 33 law firms in U.S. – HHS & FBI issued Flash alert A-000092-23B on 30 Aug 2023.

Stay secure—patch early, segment networks, and always maintain immutable, offline backups.