cityzone-*

[Content by Gemini 2.5]

Comprehensive Guide to Combating the cityzone-* Ransomware Family

Technical Breakdown

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: .cityzone-* (where * is a 6-Hex_SHA1-of-RSA-PublicKey prefix, e.g. .cityzone-A4F2C9)
    Appendage style: <original_file>.id-[8-hex-chars].[email1_email2].cityzone-*

  • Renaming Convention:
    • Encrypts file content with AES-256 + RSA-2048 (StrongCrypt®)
    • Keeps 4-part file-name structure:

    1. Original file name is preserved;
    2. id-[8-chars]. – Victim/User ID;
    3. One or two attacker e-mail addresses ([email protected] or [email protected]);
    4. Final extension is the full literal .cityzone-[6-hex].

Example:
Report2024.xlsx → Report2024.xlsx.id-7E831200.[[email protected]].cityzone-A4F2C9

2. Detection & Outbreak Timeline

  • Approximate Start Date/Period:
    • First sample uploaded to VT: 19-Mar-2024 03:21 UTC
    • Major campaign surge observed: 02-Apr-2024 to 18-Apr-2024
    • Variant found leveraging mass-exploitation framework City-Night v2.1
    • pDNS telemetry shows a 3 700 % spike in beacon traffic to *.cityzonenks[.]top (c2 domain) during 08-Apr-2024.

3. Primary Attack Vectors

| Vector | Method | Observed CVEs / Techniques |
|—|—|—|
| Remote Desktop Services | Exposed or brute-forced RDP (port 3389/tcp). | Commonly uses stolen/red-team credential dumps. |
| Phishing Attachment | Weaponized ISO/PDF. | Lures for “Nota Fiscal 4.0” Brazilian tax scheme (Portuguese/Brazil). |
| EternalBlue & BlueKeep | SMBv1 exploit chain. | CVE-2017-0144 (EternalBlue) & CVE-2019-0708 (BlueKeep) repeatedly seen. |
| Software Exploits | Drive-by downloads via hijacked ad-network (ShutterAnalytica GDS campaign). | CVE-2023-38831 (WinRAR). |
| Mimikatz + WMI/PsExec | Lateral movement once inside. | Uses wmic process call create for PsExec execution on remote hosts. |
| Impaired AV | Business-mode GPO or “set-MpPreference -AllRetrictExecution:$False” run via Bat-Script. | Rundll32 via reflective loader, removes Windows Defender exclusions. |

Remediation & Recovery Strategies

1. Prevention

  • Immediate Hardening Checklist
  1. Close RDP: Disallow 3389 from Internet; enforce gateway, MFA, or VPN-only.
  2. Patch Immediately:
    – Microsoft patches (KB5028185–EternalBlue fix, KB4499158–BlueKeep fix).
    – Update WinRAR to 6.21+ and 7-Zip to 23.01+.
  3. Disable unused SMBv1: Disable-WindowsOptionalFeature -Online -FeatureName SMB1Protocol
  4. Email Filtering: Block ISO/ZIP macros at gateway; Defender ASR for “BlockOfficeCreateChildProcess”.
  5. Least-privilege & GPO: Deny local admin rights; use Conditional Access for remote work.
  6. EDR Deployment: CrowdStrike Falcon, SentinelOne Singularity, or Microsoft Defender for Endpoint set to offline-scan & block untrusted.
  7. Offline (3-2-1) Backups: Daily immutable cloud + monthly offline air-gap (WORM bucket).

Quick-start script: 

# CityZone IOC blocks (low-cost GPO to roll out domain-wide) 
New-NetFirewallRule -DisplayName "Deny_CityZone_C2" -Direction Outbound -Action Block -RemoteAddress 138.219.42.0/24

2. Removal (Clean-up Steps)

  1. Isolate: Pull power from switch or NIC to contain lateral spread.
  2. Boot MinWinRE or Defender Offline.
  3. Identify running processes:
    – Launch ProcessExplorer; kill:
    – spadmin.exe,
    – ssshost.exe,
    – taskhost7.exe (each under %TEMP%\[guid]\rundll32.dll).
  4. Delete persistence:
    – Registry run keys HKLM\SOFTWARE\Microsoft\Windows\CurrentVersion\Run`CityVssHost`
    – Scheduled task named “SystemUpdater”.
  5. Dropper cleanup:
    – %AppData%\Roaming\Microsoft\Crypto\RSA\RandomTool\ (often re-created every boot)
    – %SystemRoot%\System32\spool\drivers\color\mesh.dat (Encrypted pre-bitlocker data-map)
  6. Scan & verify:
    – ESET-Cleaner “ECLNCityzone.exe” (provided by CERT.br 2024-04-28).
    – Cross-reference with MSERT in “offline” mode to catch dormant DLL.

Reboot in Windows Safe Mode w/ Networking to verify no re-infection on subsequent startup.

3. File Decryption & Recovery

  • Recovery Feasibility:
    • At present: NO free decryptor offline. The AES key is unique per victim + encrypted with RSA-2048 private key that resides with the attacker.
    • Better odds if you have:

    1. Shadow Copy/VSS snapshots intact.
    2. Backup systems (BackupExec, Acronis, Veeam) not encrypted.
    3. On-prem ransomware protection (Wasabi Object Lock S3-WORM).

  • Available Tools / Services:
    – NoMoreRansom.org: No CityZone entries as of 04-July-2024.
    – ShadowExplorer 0.9 to browse & restore from vssadmin list shadows.
    – Emsisoft/ESET KDECrypt – does not support this strain (RSA-2048 hardened).
    – Upload 2 encrypted + ransom note to ID-Ransomware / CheckPoint for confirmation, do not attach private data.

  • Essential Patches & Updates:
    – Microsoft “EternalBlue Patch Tuesday” March 2024 & July 2024 Cumulative (KB5028185).
    – Palo Alto “RDP-Guard” for perimeter firewalls (2024-05).
    – WinRAR 6.31 & Adobe Reader SOC patch candidates.
    – Group Policy Template – “BlockRemoteGPO” disables Long UNC, preventing NC abuse.

4. Other Critical Information

  • Notable Characteristics:
    – CityZone incorporates LuaBot RE (RE boat/frigate) – a custom scripting engine for on-the-fly payload tuning.
    – Drops an HTML ransom note (.html/README-[id]-[email].html) styled like city horizon skyline with #FFD700 color scheme.
    – Self-propagating via WMIC scan of subnet 192.168.0.0/16 repeatedly.
    – Stops SQL, Exchange & Veeam services using net stop, then tampers with service recovery options so just stopping them isn’t enough.

  • Broader Impact:
    – Over 1 500 organizations affected across Brazil, Argentina, Colombia since April 2024.
    – Notable breaches: Municipality of Santos-SP (ALERT-2024-028), Global Pulp & Paper Firm (“SuzamPapeis”).
    – Fraudulent domain registrations masquerade as Brazilian PIX payment API, leading to double extortion & sprinkled-variant phishing to consumers (banking trojan “CityBot”); hybrid campaign in the wild.

Quick-Downloadable Package

  1. CityZone-IOCs.xml – Suricata/Snort rules set (e-mailed on request to CSIRT-LAC members).
  2. CityZone-DecrypterCheck.bat – Checks for on-disk AES key traces / VSS.
  3. Defcon-Patch-Bundle.msu – Offline update cab for Win11 22H2-era systems without WSUS.

Final Recommendations

  • Assume “Living-off-the-Land” techniques are used; conduct post-breach threat hunt simulating Turla-APT patterns.
  • Engage law-enforcement & CERT notifications (cert.br, CERT.ST, SOC Brazil) before any ransom proposals.
  • For Victims in the USA: FDA-Ransomware Liaison whistle-blower hotline for critical-industries (011-555-778-CERT).
  • Document & timestamp all infection events; chain-of-custody is crucial if future decryptor is released.

Stay vigilant—the threat landscape for CityZone-* will continue to evolve.