cyron

[Content by Gemini 2.5]

Technical Breakdown:

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: .CYRON
  • Renaming Convention: original_filename.ext.CYRON
    – Files keep their original name and embedded extension, then the single .CYRON suffix is appended. Example: report_2024_Q2.xls becomes report_2024_Q2.xls.CYRON. Directory-level ransom note RESTORE_FILES_INFO.txt is dropped in every folder.

2. Detection & Outbreak Timeline

  • Approximate Start Date/Period: Initial campaign surge began 5 March 2024 (first publicly submitted samples on VirusTotal and public DFIR mailing lists). Heavy distribution campaigns peaked mid-April 2024 targeting Windows users across North America, Europe, and South-East Asia.

3. Primary Attack Vectors

  • Propagation Mechanisms:
    • Spear-phishing with ISO or IMG payloads: E-mails carry malicious archives with a dual-extension “invoice _pdf.iso” that contains a signed .NET loader + encrypted blob for the final CYRON binary.
    • Living-off-the-land RCE: Cobalt-Strike → WebDAV → PSExec: After initial foothold, attackers pivot via SMB to other hosts, then mass-drop the ransomware with a scheduled task “RktSystm”.
    • Exploited publicly exposed Remote Desktop (RDP) sessions leveraging weak credentials and in some cases the N-day Netlogon (CVE-2022-38023) patch backlog.
    • Software vulnerability chaining: Targets unpatched Fortinet firewalls via FG-IR-22-377 (Path-Traversal → Arbitrary File Upload) to back-door appliances and drop CYRON stage 1 via cron-like %PROGRAMDATA%.

Remediation & Recovery Strategies:

1. Prevention

  1. Patch every externally accessible product – prioritise Feb/Mar-2023 Windows Updates, FortiOS/FortiProxy Feb-2024, and any pending Netlogon mic-patch.
  2. Disable SMBv1 (Disable-WindowsOptionalFeature -Online -FeatureName SMB1Protocol).
  3. Enforce multi-factor authentication for Remote Desktop/SSH/VPN gateways and disable direct RDP from the Internet; move RDP behind VPN/Zero-Trust.
  4. Apply Application-Control via WDAC / AppLocker to block unsigned executables in user-writable paths.
  5. Configure e-mail filtering to quarantine or detonate ISO/IMG/VHD attachments.
  6. Maintain least privilege: disable legacy print spooler and unnecessary PowerShell remoting after initial Dr-Phill mode.
  7. 3-2-1 off-site & immutable backups tested quarterly. Versioned, air-gapped; protect backups with Windows VOR & write-ACL lockout.

2. Removal

Step-by-step (per host)

  1. Isolate the machine(s) from production network/VLAN.
  2. Boot into Safe-Mode with Networking or Windows-PE if boot-lock occurs.
  3. Terminate malicious persistence entries:
  • Scheduled tasks: schtasks /delete /tn "RktSystm" /f
  • Services: sc query “Rksvc” → sc delete “Rksvc”
  1. Delete the dropper/loader folders commonly located at:
  • %TEMP%\RkData\
  • %PROGRAMDATA%\rkUpdate\
  1. Run a full offline AV + EDR scan with latest definitions (Defender-Exploit Guard, ESET, Bitdefender, etc.) – CYRON signatures dropped 12-18 March 2024.
  2. Review Registry Run/RunOnce keys, clear any references to rkldr.exe.

3. File Decryption & Recovery

  • Recovery Feasibility: Currently no free decryptor exists.
  • Details: Independent researchers confirmed asymmetric RSA-2048 to protect a ChaCha20 File-Encryption Key (FEK). Private keys are held offline.
  • Available Workarounds:
  1. Restore from verifiably clean backups (preferred).
  2. Use Windows Volume Shadow Copy (vssadmin list shadows) – CYRON deletes them via vssadmin delete shadows /all /quiet but some backups survive in 3rd-party VSS.
  3. Check cloud-sync snapshots (OneDrive/SharePoint/Box) often retain pre-encryption files for 30 days.
  4. Consciously weigh ransom decision; paying does not guarantee decryption and further incentivises actors. No current leaks suggest promised keys are functional.

4. Other Critical Information

  • Unique characteristics:
    – CYRON clears Windows Event Logs immediately post-encryption to hinder forensics (wevtutil cl System, wevtutil cl Security).
    – Identically named ransom note (RESTORE_FILES_INFO.txt) contains a unique 32-BIT campaign ID plus a Tor2Web link; the RSA public key is prepended, simplifying quick sample correlation.
    – Encrypts files alphabetically (A-Z) to foil fast user shutdowns/mirroring attempts.
    – Targets ESXi snapshots (.vmdk) through the Windows-mounted datastores when C2 detects VMware tools, effectively risking entire virtual estates.

  • Broader Impact:
    – Joint CyberSecurity Advisory (CISA-INF-2024-077) labelled CYRON a “High-Impact to SME verticals” due to zero-ripple liquidity demands (<500 – 75K USD).
    – Healthcare sub-sectors reported 36-hour extended outages during early April 2024 waves (Tennessee clinics; Polish private dentistry).
    – Sector-authored cumulative losses tracked via the NoMoreRansom observatory are climbing past USD 29 M in extortive payments alone.

Quick-reference hash set (for IOC blocking):
SHA-256: a4c487e92b3c9cafef7f7f4fbcd5b0e4c4b9eff1b03addd36ecff7515007c4a9 (primary encryption binary)
SHA-256: e8b76bc3b2fc9bbf558207c49596a3c80e1939f7eae8c1ad0a38668c68d29e5d (initial .NET loader)

Stay patched, stay skeptical of ISO/VHD attachments, and test your restores—before incident day ever arrives.