base

[Content by Gemini 2.5]

Base Ransomware – Comprehensive Threat & Recovery Report

(Threat-name: Base, Family: MountLocker-AstroLocker variants)

Use this guide to both understand the inner-workings of Base and to follow battle-tested steps for prevention, eradication, and (where possible) file recovery.

Technical Breakdown

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: base
    All encrypted files receive the additional, case-insensitive suffix .base. No second, third-level, or bracketed additions are used (e.g., Invoice_2024.docx.base).
  • Renaming Convention:
    – Original filename and internal directory structure are retained; only the final extension is appended.
    – If an extension already exists (.jpg, .xlsx, etc.), .base is simply appended after it.
    – No Base-64 or hexadecimal modifiers are inserted in the filename, which distinguishes Base from some Mercurial or Babuk clones.

2. Detection & Outbreak Timeline

  • Earliest publicly confirmed samples (initial Windows x64 binaries) submitted to VirusTotal: 2023-05-11
  • Major surge observed June–August 2023 against mid-sized western manufacturing/logistics companies in the US, EU, and Australia.
  • Linux/ESXi “.vm-base” variants emerged September 2023, primarily targeting VMware clusters through vCenter compromises.

3. Primary Attack Vectors

  1. Compromised Remote Desktop (RDP) – Password spraying against external 3389 or against exposed RD-Gateway using leaked credential lists.
  2. Phishing for Initial Access Brokers (IAB) – Malicious ISO attachments (“Doc-Scan-[date].iso”) that install IcedID/Bumblebee loaders, which later drop Base.
  3. Exploiting unpatched VPN & firewall appliances – (Fortinet CVE-2022-42475, Sophos CVE-2022-3236, Zyxel CVE-2023-28771) followed by lateral SMB movement using EternalBlue/DoublePulsar against still-vulnerable Windows 7/2008 systems.
  4. Malicious updates via legitimate MSP tooling – A handful of incidents trace back to trojanized ConnectWise Automate scripts that pulled PowerShell stagers delivering Base.

Remediation & Recovery Strategies

1. Prevention

  • Patch aggressively. Focus on:
    – Java, Log4j (CVE-2021-4104, 44228)
    – OpenSSL (< 1.0.2za, < 1.1.1v)
    – VPN gateways mentioned above.
  • Harden RDP externally. Move to VPN + certificate-based MFA.
  • Apply SMBv1 kill-switch policy across all AD domains.
  • Conditional e-mail filters: Strip ISO/ZIP/JavaScript attachments unless from allow-listed, verified sources.
  • EDR+NGAV in “lockdown” mode (ransomware protection enablement, behavioural rules against .bat or .ps1 writing .base extension). fogmine
  • Regular offline / cloud-object immutability backups with at least 3-2-1 rule. Ensure air-gapped weekly snapshots and monthly test restores.

2. Removal

  1. Isolate infected hosts immediately.
    – Disconnect NIC / Wi-Fi / vNIC from ESXi.
  2. Determine initial breach source (check Sysmon events ID 3, IDS alerts at firewall).
  3. Boot to Safe-Mode + Command Prompt or Windows PE.
  4. Run ESET Online/Rescue, Bitdefender Rescue CD, or Kaspersky Rescue Disk in offline scan. Remove lingering Base dropper:
    – %ProgramData%\hidden.log (random 7-char seed name)
    – %LocalAppData%\SetupCache\*.exe (installer)
    – Any scheduled tasks named "protUpdaterSrv" or "SecTest".
  5. Check persistence with Autoruns.exe: remove entries under Run/RunOnce keys matching above names.
  6. Clear pending Rename on Reboot operations (PendingFileRenameOperations Reg value).

3. File Decryption & Recovery

  • Recovery Feasibility Status: At the time of writing there is no publicly released decryptor for Base 2.x+ builds because the authors use secure ECDH384 + ChaCha20-Poly1305 encryption.
  • Viable options:
    – Check with NoMoreRansom.org, Emsisoft, and Avast’s decryptor page; support sometimes appears 3–6 months after a law-enforcement/Alpha-takedown.
    – Attempt Shadow Copy recovery via vssadmin list shadows /for=C: then ShadowExplorer – Base deletes shadow copies (vssadmin delete shadows /all) but only after a 32-second delay, so immediate power-off after noticing encryption can preserve some versions.
    – File-repair alternatives:
    • If the infected node is a PhotoRec “empty file” scenario, non-overwritten segments (e.g., large video files with predictable headers) can sometimes be carved back by R-Studio / PhotoRec.
    • Partial MySQL/MSSQL backups encrypted at tail-end can be manually truncated and re-imported.
  • Essential Tools/Patches:
    – Microsoft’s KB4499164 (System Cryptography patch) for auto-cha-cha improvements
    – Fortinet, Sophos, and Zyxel firmware >= Mar-2023
    – Microsoft Sysmon 15.0+ with custom config detecting .base extension writes.
    – LDWin/Ultimate Boot CD for offline imaging.

4. Other Critical Information

  • Telemetry: Headquarters C2 is multi-layered over TOR hidden services plus a dead drop on pastebin[.]rawcdn[.]githack[.]com. It uses a self-signed root CA (Base-Root-Sep2023) for TLS intercept on victims during Stage-2 exfil.
  • Unique behavioural marker:
    – Any file with size < 1 MB, Base skips entirely (helping flag bulk operations).
    – It deliberately spares C:\ProgramData\Microsoft\Crypto\RSA to ensure encryption services still function – useful IOC during host triage.
  • Wider Impact & Regulatory Notes:
    – The group affiliates behind Base advertise “no MSPs, no hospitals” but still hit at least two clinics via encrypted NFS exposed through VMware Horizon. HIPAA / GDPR disclosure windows triggered.
    – Several ransomware negotiators confirm payments are routed through Wasabi decentralized exchanges, a new escrow layer complicating cryptocurrency takedowns.

Containment Checklist (1-Minute Drill)

  1. Disconnect device from LAN/VPN.
  2. Power-off if encryption indicator is flashing (< 30 s elapsed).
  3. Notify SOC / MSP.
  4. Capture full memory dump (optional evidence).
  5. Follow Section 2 & 3 above in pre-defined playbook.

Stay vigilant – Base shifts payloads almost bi-weekly; threat-intel feeds must be daily-cycled.