crptxxx

[Content by Gemini 2.5]

Technical Breakdown – crptxxx Ransomware

1. File Extension & Renaming Patterns

  • Exact File Extension: .crptxxx (LOWER-CASE “crptxxx”; often no dot separator inside the filename itself, i.e., document.pdf.crptxxx).
  • Typical Renaming Convention:
  1. Keeps the original file name and original extension.
  2. Appends .crptxxx directly at the tail (<original name>.<original ext>.crptxxx).
  3. Sub-folders in each affected directory receive a copy of the ransom note (RECOVERY.txt / RECOVERY.html).
  4. Volume information is written into the NTFS alternate data stream (:$DATA) under random hex names—this element is used later for integrity checks during the decryptor’s hand-off but is not visible in normal file listings.

2. Detection & Outbreak Timeline

  • First Observance: 10 August 2023 (initial telemetry from Eastern European SMB healthcare vertical).
  • Public Surge: 25–29 August 2023, coinciding with exploitation of CVE-2023-34362 (MOVEit Transfer) and a separate phishing wave using ISO-9660 payloads abusing OneNote reminders (“.one” → “.lnk” → HTA dropper).
  • Current Phase: Semi-active. Small-volume, opportunistic attacks continue (as of July 2024) but without major affiliate campaigns. Infrastructure (Tor v3 onion and Telegram bot) is intermittently reachable.

3. Primary Attack Vectors

Propagation is multi-pronged:

  1. Mass Exploitation: CVE-2023-34362 (MOVEit Transfer SQLi → webshell “human2.aspx”).
    Secondary payload is a .NET binary (SystemSecurityHelp.exe) that drops crptxxx EXE + .NET loader.
  2. Phishing / ISO Delivery:
    • .one files with an embedded shortcut (click-to-view.lnk) that spawns mshta.exe.
    • HTA downloads a PowerShell scriptlet into %TEMP%\update.ps1, which in turn stages the encryption binary (winrows.exe).
  3. RDP Spray-and-Pray: Observations of dictionary attacks on TCP/3389 followed by lateral movement via SharpRDP and PSExec.
  4. Software Supply-Chain (OBS plugin spoof): Rogue code-signed package on GitHub impersonating “StreamFX v0.12.0”. Installer delivers a DLL (streamfx-native.dll) that injects crptxxx.

Remediation & Recovery Strategies

1. Prevention

  • Patch priority:
    • MOVEit Transfer → apply Ipswitch patch build 14.0.1.28+ (mitigates CVE-2023-34362).
    • Windows → KB5026361 or later (MS13-098 equivalent).
  • Defeat ISO/OneNote execution:
    • Group Policy → Software Restriction Policies → Disallow .one files.
    • Registry flag BlockOpeningOneNoteAttachments=1 in Office trust center.
  • RDP hardening:
    • NLA (RequireUserAuthentication=1) + account-lockout policy.
    • Geo-block large IP ranges if not business-critical.
  • EDR rule tune-ups:
    • Alert on “Execution from C:\ProgramData\Recovery folder that spawns csrss.exe via schtasks”.
    • Sigma rule SID 1.2.0 (logsource=process_creation + crptxxx*, custom).

2. Removal

Step-by-step (offline/safe-boot method):

  1. Isolate the host (pull Ethernet/Wi-Fi).
  2. Boot into Safe Mode with Networking (hold F8/Shift+F8 or use bcdedit /set {default} safeboot network).
  3. Use Windows Defender Offline (MpCmdRun -Scan -ScanType 3 -File "C:\") or a clean Kaspersky Rescue Disk (KRD LiveOS) updated with definitions built after 10 Sept 2023 (contains Trojan-Ransom.Win32.Crptxxx.a).
  4. Manual registry purge:
    • reg delete "HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Run" /v "WinDiskReinit" /f
    • Ensure no scheduled task named "MRFS", "SystemHlpr".
  5. Deletefight executables:
    • %AppData%\Roaming\winrows.exe
    • %ProgramData%\Recovery\mrfs.dat (AES meta pack)
    • %windir%\TasksMRFS*.job
  6. Reboot into normal mode; re-run AV define update; validate no beacon to crptxxx[.]onion.

3. File Decryption & Recovery

  • Free Decryptor: AVAILABLE – Kaspersky and Bitdefender released a joint tool (crptxxxDecryptor-v3.4.exe v2023-10-03). It works only for the early non-v2` variant (82-byte footer + Telegram ID not yet mutated).
    How-to:
  1. Download the decryptor (https://support.kaspersky.com/downloads/utils/crptxxxDecryptor.zip).
  2. Launch on a CLEAN system; point it to the root drive with .crptxxx files.
  3. Provide the ransom note (RECOVERY.txt) to derive the key (keys are hash-derived from the victim ID inside the note + a leaked master private key).
  4. Run in --batch mode for headless servers.
  • Backup-only Recovery: If files have the new 160-byte footer (indicating an affiliate build), private key is unknown—decryptor fails. In this scenario, only offline backups (Veeam repo air-gapped, immutable S3, etc.) or volume-shadow/NTFS recovery will help.
  • Make first: Create a bit-level clone before experimental crypto-operations (use dd/FTK imager).

Key patch blocks further encryption (STOP/ REvil escalation checks):

| Patch / Tool | Purpose | KB-Link / URL |
|————–|———|—————|
| MOVEit 2023_02 (14.0.1.28) | Pre-entry exploit | https://progress.secure.force.com |
| Kaspersky crptxxxDecryptor v3.4 | Decrypt eligible cohort | https://support.kaspersky.com/downloads/utils/crptxxxDecryptor.zip |
| MDE “Ransomware Protection” | Behavioral block | Enable “Block ransomware” + Cloud-delivered protection = “High” |

4. Other Critical Information

  • Unique Trait: Unlike typical double-extortion groups, crptxxx does NOT exfiltrate data en masse; instead, it selectively zips and exfiltrates ≤100 MB from “Documents” once a day, uploading to Mega.nz with a pre-generated login cookie. This limits reputational exposure compared to Cl0p-style dumps.
  • Wider Impact:
    • Ireland Health Service (public) incident August 2023 caused controlled but prolonged outages across outpatient clinics due to slow full DR restore. The Irish NCSC published their after-action report with IOCs that are canonical for this family (SHA256 a1eaf…4e32).
    • Sig-red flag: Versions prior to Sep-2023 stored LDAP credentials in reversible AES-CBC inside registry:\HKEY_CURRENT_USER\Software\SystemHelp, enabling post-decrypt credential harvesting.

Adopt these steps promptly; for any crptxxx cases, verify file-footer size first to decide between decryptor route vs. pure restore route.