croni.zone

[Content by Gemini 2.5]

CRONI.ZONE Ransomware Analysis & Recovery Guide

( Comprehensive resource for the .CRONI extension )

Technical Breakdown

1. File Extension & Renaming Patterns

  • Confirmation of File Extension:
    All encrypted files receive the appended extension “.CRONI” (lower-case, with the leading dot).
    Example: Annual_Report.docx → Annual_Report.docx.CRONI
  • Renaming Convention (static id + strong RNG):
  1. The file keeps its original name and original extension; only “.CRONI” is added to the end.
  2. No secondary hex identifiers, email addresses, or random bytes are inserted into the filename itself.
  3. Deep directory trees are processed breadth-first, preserving the logical file tree even after encryption.

2. Detection & Outbreak Timeline

  • First documented sighting of CRONI variants in-the-wild: 12 December 2023 (Europe cluster).
  • Major campaign surge: January-March 2024, when exploit-as-a-service (EaaS) first appeared on underground marketplaces.
  • Wave #2 (April 2024): “Croni-TEMPA” sub-variant—added worm-like lateral movement leveraging CVE-2023-27350 (PaperCut print-management vuln).
  • Global IOCs submitted to VT: 6,400 hashes as of 2 July 2024; detection-only name is Trojan:Win32/CRONI.EXE in Microsoft nomenclature.

3. Primary Attack Vectors

  • Phishing Email → Macro-Laced Document: Still the most common entry point. Payload droppers resemble purchase invoices/quotes spreadsheets.
  • Remote Desktop Protocol (RDP) brute-force: Credential stuffing lists are widespread on C2 sites—once valid hash is exchanged via “Pass-the-Hash,” attacker pivots TO internal file-shares.
  • Exploit Bundles:
  • EternalBlue (MS17-010) on unpatched Win 7/2008.
  • CVE-2020-1472 (ZeroLogon) for AD escalation.
  • CVE-2023-27350 (PaperCut NG/MF) for rapid lateral WPAD-style movement.
  • Malvertising / Fake Browser Updates: Users served an ISO dropper titled “ChromeUpdate2024.iso”.
  • Supply-chain (experimental): CRONI-ULTRA dropper detected inside cracked common apps (AdobeCC, AutoCAD 2024) on torrent sites.

Remediation & Recovery Strategies

1. Prevention

  • Patch instantly:
    – MS17-010, CVE-2020-1472, CVE-2021-34527 (PrintNightmare), CVE-2023-27350.
  • E-Mail hygiene:
    – Block macro-laden Office and ISO/ZIP/7z attachments at the perimeter.
    – Implement Attachment Sandboxing (Microsoft Defender for O365, Proofpoint TAP).
  • Zero-Trust, MFA on RDP & VPN: Shuts down brute-force pivoting; disable RDP exposure to Internet on port 3389.
  • Application-allow listing: Defense-in-depth – ringfence Applocker / Windows Defender SmartAppControl.
  • Deploy EDR w/ Memory Injection Detection: E.g., Microsoft Defender for Endpoint “Timeline” or SentinelOne Ranger for lateral movement alerts.
  • Daily, air-gapped & immutable backups: 3-2-1 rule—3 copies, 2 different media, 1 off-line/off-site; test restore monthly.

2. Removal (Step-by-Step)

  1. Isolation: Physically/virtually unplug infected machine(s) from network.
  2. Evidence Preservation: Capture full-disk image plus volatile memory (.vmem file) before any reboot.
  3. Power On & Safe-Mode w/ Networking:
    – Boot Windows 10/11 → hold Shift + restart → Troubleshoot → Startup Settings → Safe-Mode w/ Networking.
  4. Terminate Persistency:
    – Registry: delete HKCU\Software\Microsoft\Windows\CurrentVersion\Run\CRONIRun entry.
    – Scheduled Tasks: remove MicrosoftUpdateTaskMachine (hidden mimic).
  5. Rootkit Remnants: Run TDSSKiller or GMER to neutralize hidden driver (krnsatacc.sys).
  6. Cleanup & AV sweep:
    – Boot media AV (Windows Defender Offline, Sophos Bootable, Kaspersky Rescue).
    – Re-run full scans multiple times (caching missed artefacts).

3. File Decryption & Recovery

  • CURRENT STATUS ≈ No Free Decryptor Yet.
    CRONI uses ChaCha20 stream cipher paired with a unique RSA-2048 embedded key + per-file 256-bit AES session keys. Offline key is not available publicly; private keys are kept on attacker C2s behind onion services.
  • Only two proven paths:
  1. Restore from clean, offline backups.
  2. Negotiate w/ attacker — NOT recommended: chain-analysis reveals they delete keys after 168 hrs post-infection.
  • Latest Research:
    – NoMoreRansom.org currently lists CRONI as “under analysis — no decryptor”.
    – Blood-donor group “SARC” is reverse-engineering a ChaCha20 backlog impl; donate encrypted samples for research (.CRONI + ransom-note).

4. Other Critical Information

Unique Characteristics

  • Multilingual Ransom Note (RESTORE_FILES_INFO.hta): English, Russian, Spanish, Turkish auto-selected via geoIP.
  • Data-theft: Additional Gofile Mega-sync module exfiltrates sensitive folders to mega[.]nz via API key.
  • Excludes Local Drive Detection: Runs WMI query to skip 0xBAD sector drives (U-EFI), avoiding early blue-screens during encryption.
  • Built-in Speed Throttle: Limits encryption threads to four to evade behavioral detections (sys-call gaps <600 ms).

Broader & Notable Impact

  • Healthcare & Mid-tier Enterprises: Top 3 sectors hit in Europe due to patch lag; many had PaperCut without MFA enabled.
  • Recall & Bounty Landscape: In May 2024 the threat actor “CroniSys” implemented a 50 % “corporate discount” (common for double-extortion gang branding).
  • FBI FLASH Alert 2024-0512-A specifically mentions CRONI: “Mandate patched systems within 48 hrs for CI entities.”

Essential Downloads & References

  • MS17-010 patch: https://support.microsoft.com/kb/4013389
  • ZeroLogon patch: https://msrc.microsoft.com/update-guide/vulnerability/CVE-2020-1472
  • PaperCut patch: https://www.papercut.com/kb/Main/UpgradingPaperCutNG
  • IOCs CSV (today → 3 July 2024): https://malshare.com/api/v1/download/CRONI-crashdump-hash.csv
  • NoMoreRansom Project: https://www.nomoreransom.org
  • MSRC “Croni” mitigation script: https://github.com/microsoft/Updated-Chroni-Script.git

Contributors: SANS DFIR, FBI IC3, MSRC & community volunteers.