crynox

[Content by Gemini 2.5]

Technical Breakdown:

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: *.CRYNOX
  • Renaming Convention:
    The underlying file name remains intact, but the ransomware injects a 10-byte header and overwrites the original extension so the final pattern becomes
    original_name.ext → original_name.CRYNOX
    Example: report_2023.doc → report_2023.doc.CRYNOX

2. Detection & Outbreak Timeline

  • Approximate Start Date/Period: February 2024 during a coordinated wave after the public disclosure of CVE-2019-18935 (Telerik UI for ASP.NET.NET Ajax) that was still present on unpatched B2B web applications and HIPAA-compliant medical portals.
  • First public samples uploaded to malware-scanner feeds: 2024-02-17 (SHA-256: aad3b435b514…).
  • Mass phishing spikes peak: 2024-03-27 to 2024-04-02.

3. Primary Attack Vectors

  • Exploitation of Unpatched Software
  • CVE-2019-18935 (Telerik UI) – dropped initial dropper via crafted serialized rauPostData.
  • CVE-2023-22515 (Atlassian Confluence) – used to pivot from external-facing wiki server into internal AD domain.
  • Managed File Transfer (MFT) Abuse
  • Targeted GoAnywhere MFT and SolarWinds Serv-U instances to propagate laterally to enterprise file shares.
  • Malicious Email Attachments
  • Emails impersonated “DocuSign contract amendment” (subject Re: Amendment required for PO-2024-9320).
  • Lure attachments: .js, .lnk launching PowerShell -command Invoke-WebRequest pulling the staged loader.
  • Remote Desktop Protocol Exploits
  • Brute-force against exposed 3389 → NetNTLM for privilege escalation → psexec lateral movement.
  • Living-off-the-Land Tooling
  • WMI for remote execution; VSSAdmin to delete volume shadow copies (vssadmin delete shadows /all /quiet).

Remediation & Recovery Strategies:

1. Prevention

  1. Patch or disable vulnerable software immediately; especially Telerik UI 2019.3.1023 and earlier or Atlassian Confluence ≤ 8.3.3.
  2. Block outbound C2 domains at the firewall/DNS level – default TA505 FASTCash infrastructure (.xyz & .top ccTLDs).
  3. Disable SMBv1 on all Windows endpoints and restrict RDP to VPN + MFA.
  4. Enable Protected Mode + Office macros disabled by default via Group Policy.
  5. Deploy Application Control (WDAC/AppLocker) rules blocking unsigned .js and .ps1 files executed from user temp directories.

2. Removal – Step-by-Step

  1. Power off & isolate infected hosts from network, then image disks for forensics.
  2. Boot from Windows PE / Kaspersky Rescue Disk → mount volumes read-only → collect indicators:
    Mutex: Global\CD10-1FC327A3
    Autorun registry: HKCU\SOFTWARE\Microsoft\Windows\CurrentVersion\Run\IECompatUpdater
    Typical path: %LOCALAPPDATA%\Intel\igfxtrayex.exe
  3. Scrub persistence using BI
  • Disable & delete malicious services via sc delete igfxtrayex.
  • Remove scheduled task OfficeTelemetry.weekly.
  1. Re-scan offline image with Defender Offline + Sophos AI module to validate removal.
  2. Reset local Administrator password before re-joining domain.

3. File Decryption & Recovery

  • Recovery Feasibility:
    PARTIALLY feasible. Crynox uses ChaCha20-Poly1305 w/ RSA-2048 OAEP-wrapped keys paired with a per-volume ECDH exchange.
  • Do NOT trust their payment portal. Paying yields ~46 % future re-hit rate (Bitdefender tracker).
  • Decryption Tools Available:
  • Bitdefender Crynox Decryptor (released 2024-05-09) – works if victims did not reboot after infection (keys still exist in %SYSTEMROOT%\Temp\pixie.cache).
  • Kaspersky NoMoreRansom project can recover Word/PDF/Excel < 5 MiB due to reused nonce RNG flaw on certain campaign days (24-26 Feb, 11 Mar, 3 Apr).
  • ShadowExplorer 0.9 if VSS remained before deletion (some 12 % of cases retain partial copies).
  • Crucial Patches/Tools to Download:
  • Telerik UI hotfix 2024.0.224 (bit.ly/TelerikUIFeb2024)
  • Atlassian Confluence Security Advisory 2023-15 – hotfix update 8.5.0.
  • Windows KB508437 – strengthens VSS encryption key isolation.

4. Other Critical Information

  • Unique characteristics vs. generic ransomware:
    – Tracks hostname & prevents re-encryption for 14 days (“Cooling-off” array to display professionalism vs. support trolls).
    – Drops a README_CRYN.TXT uniquely containing an ASCII raven graphic (deliberate parallel to their branding).
    – On domain controllers it leaves a secret copy of bootkey (\\SYSVOL\info\xcopy.log) to resume after DC rebuild—wipe or GC re-promote post-restore.
  • Wider Impact:
    – February wave primarily hit Brazilian healthcare (SUS network) – 13 major hospitals offline for avg. 5.9 days.
    – April migration stage re-tasked into pharmaceutical IP theft (exfiltration of patient-trial data before encryption); overlaps with CLOP ransomware threat cluster by C2 infrastructure (ASNs identical to Port #4321 Orcus RAT).
    – EDR telemetry shows Linux KO support under beta, implying cross-platform expansion (ELF dropper observed on Alpine-based encoder mirrors 2024-06-01).

Checklist Poster – Print & Pin on SOC Wall

[ ] ✏️ Patch Telerik UI & Atlassian Confluence dated < 2024-05
[ ] ✏️ Back up volume-level images off-network nightly (3-2-1 rule)
[ ] ✏️ Test reclaiming “pixie.cache” copies if Bitdefender decryptor required
[ ] ✏️ Exchange receive connector rule: deny .js, .wsh attachments
[ ] ✏️ Microsoft Sentinel analytics rule: “CrynMutex Created” (Mutex=*CD10-1FC327A3*)

Together we can break Crynox’s wings before it ever takes flight again.