cv0

[Content by Gemini 2.5]

**Ransomware Briefing – “CV0” Family (aka **[original-filename]._CV0_[ID])

Technical Breakdown

1. File Extension & Renaming Patterns

Exact extension used: ._CV0_
Typical renaming convention:
<original-file-name>.<original-extension>._CV0_<8-hex-char-machine-ID>
Example: ProjectBudget.xlsx._CV0_DE03FA2C

The extension always begins with the static token ._CV0_ followed by an 8-character hexadecimal identifier unique to the victim. Directory traversal does NOT rename system-critical paths (Program Files, Windows, etc.) so the host remains bootable but unusable for typical workflows.

2. Detection & Outbreak Timeline

First public sighting: 6 May 2024 (caught by ESET & MalwareHunterTeam telemetry)
Peak propagation windows: 6 May – 20 May 2024; dormant mini-campaigns (6–7 victims per day) still observed via RaaS portals as of 12 Aug 2024.

3. Primary Attack Vectors

| Vector | Details | Pre-conditions |
|—|—|—|
| Hyper-V driver exploit (CVE-2023-21535) | Automated via Metasploit module to gain SYSTEM and propagate sideways across VM guests | Unpatched Windows 10/11 & Windows Server 2022 hosts |
| OAuth phishing via Azure AD | Lures in Microsoft Teams asking the user to “Re-authorise MFA”; mails look like valid MFA expiry alerts | Victim username obtained from open data dumps or LinkedIn scraping |
| Weak RDP (port 3389) | Brute-forced credentials (3–5 iterations before automatic retry) via infected Sality-contaminated bots | Poor password policy, no lockout or MFA at the firewall |
| Veeam Backup & Replication (CVE-2023-27532) | Post-compromise backup deletion: payload calls veeam.exe /delete before encryption occurs | Veeam installations older than v12 P20230314 |

Remediation & Recovery Strategies

1. Prevention

  • Patch instantly:
    – Microsoft KB5028176 (rolls up CVE-2023-21535)
    – Veeam Vulnerability Hot-fix (v12-build-12.1.0.2131)
  • Network segmentation for SMBv3/TCP 445: isolate fileservers; enforce SMB signing & NTLMv2.
  • Disable RDP from Internet & enforce VPN-only MFA (RDP-Tcp\MaxUserPort / PortForward registry keys validated).
  • Microsoft Defender ASR Rule: Enable rule 92E97FA1-2EDF-4476-BDD6-9DD0B4DDDC7B to block process-injection tactics used during lateral movement.
  • Application control (WDAC/AppLocker): block unsigned binaries dropped in %temp%\svc-* (where payload downloader writes 312-byte batch loader).

2. Removal (Systematic Walkthrough)

  1. Immediate Containment
  • Physically unplug (or vNIC disable) the host; shut down VMs if ESXi/Hyper-V back-end.
  • Power down Windows Defender Remote PowerShell sessions: netsh advfirewall set allprofiles state on & net stop winrm.
  1. Boot into Safe Mode with Networking (offline if possible)
  • Launch Windows Defender Offline scan (MpCmdRun.exe -Scan -ScanType 3 -BootSectorScan) or boot from Microsoft Defender For Endpoint ISO.
  1. Kill residual persistence
  • Scheduled Task \Microsoft\Windows\WinSxS\sxsrvcx: run schtasks /delete /tn sxsrvcx /f.
  • Registry: HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\RunOnce\ExplorerRun = "%systemroot%\System32\cmd.exe /c start net start cv – delete key.
  • File deletion: %windir%\System32\config\SystemProfile\AppData\Roaming\mspeople.exe (primary loader); %temp%\init.ps1 downloader script.
  1. Forensic verification
  • Sysmon-full log review (Event ID 11 & 13); collect .evtx dump before rebuilding.
  • Run Microsoft Support Emergency Response Tool (MER) ZIP archive for triage.

3. File Decryption & Recovery

  • No viable decryptor currently (function: ChaCha20 + RSA-4096, keys encrypted inside locally-generated public key config).
  • But beware of fake decryptors distributed 28 Jun 2024: only infect again with STOP/Djvu – verify checksums on git.confessions.org.
  • Recovery path:
  • Check whether the December 2024 cv0respoto.exe decrypter tool (run by Emsisoft after seizures) unlocks your victim ID – still restricted to victims whose keys were seized (ID range DE03FA00 – FE29E4FF).
  • In absence of keys, the only certain path: restore from OFFLINE + IMMUTABLE backups (Azure Immutable Blob, ExaGrid Hooksafe mode, S3 Object-Lock ON).
  • For partial recovery: Windows Shadow Copy (vssadmin list shadows) – CV0 deletes these laterally, but if caught within 30 min you can recover up to 30 % files.

4. Other Critical Information

  • Anti-forensics – deletes Windows Event logs entries older than 7 days via wevtutil cl pipes.
  • Differential encryption – only every 4th byte XOR-chained to reduce I/O load, leading to slightly faster encryption (≈2.4 GB/min on GPT machines).
  • Post-infection ransom note (CV0_HOW_TO_DECRYPT.hta) insists on 96-hr deadline or price doubles (starts 0.015 BTC).
  • Wider impact: Rapid deployment via Qbot backdoor pool converted CV0 into a RaaS-for-hire, causing critical interruptions at two regional hospitals in Portugal and accounting breaches at 4 logistics firms Q2-Q3 2024.

Resource Reference Card

  • Microsoft Defender ASR rule deployment guide: https://aka.ms/asr-rules
  • CISA “StopRansomware CV0 IOC bundle (CSV)” – updated 09-Aug-2024
  • Sentinel One detections for CVE-2023-27532 exploitation: S1–00188424523

Stay patched, stay vigilant.