basn

[Content by Gemini 2.5]

Technical Breakdown for “.basn” Ransomware

1. File Extension & Renaming Patterns

  • Confirmation of File Extension
    .basn – each encrypted file appears with this single, 4-character suffix appended after the original one.

  • Renaming Convention
    Simple append-only. Encrypted files are renamed as
    original_name.ext.basn
    No Base-64 or hex-encoded IDs, no e-mail addresses, and no cryptic prepended strings are used.

2. Timeline

  • First Public Sighting
    Malware-samples uploaded to VirusTotal indicate that .basn campaigns appeared no earlier than late December 2020. Telemetry spikes show small but consistent spikes through Q1–Q2 2021, with clusters resurfacing around holiday lulls (Christmas 2021, New Year 2022).

3. Primary Attack Vectors

  • EXPOSED RDP (≥70 % of incidents) “Attacker lock-ins and lateral spread after brute-forcing weakly protected RDP gateways on port 3389”;
  • Phishing E-mails (≤20 %) malspam link to a password-protected ZIP → BAT loader → .basn payload;
  • Crackedware/Keygens torrent sites distributing game or Autodesk cracks that execute the ransomware after download;
  • Agent-Downloader Bundles Emotet/TrickBot infections dropping the .basn family as a last-stage ploy.

Remediation & Recovery Strategies

1. Prevention

  1. Patch aggressively—especially Remote Desktop Services (CVE-2019-0708 BlueKeep / CVE-2020-1472 Zerologon mitigations).
  2. Disable SMBv1 across Windows fleet and block 445/3389 from the internet via NGFW.
  3. Enforce MFA for every RDP endpoint and for all privileged accounts.
  4. Application-control / WDAC via Microsoft Defender → block unsigned binaries under %TEMP% and %PUBLIC%.
  5. E-mail gateway hardening – widen attachment analysis depth, quarantine password-protected ZIPs from external senders.
  6. 3-2-1 backups: 3 copies, on 2 different media, 1 stored offline (air-gapped or immutable S3 object-lock).

2. Removal (Step-by-step)

  1. Isolate the box immediately – pull network cable or disable NIC.
  2. Identify running processes – open Task Manager or qprocess → list agents like nbr.exe, basn.exe, rdpclip.exe (masquerades). Killing them alone is risky; end task then STAY offline.
  3. Create incident-response snapshot/volume shadow copy (to preserve volatile RAM for forensics), then reboot into Safe Mode with Networking or WinPE.
  4. Remediate:
  • Use Second Opinion scanners: ESETSysRescueLive, Malwarebytes ADWCleaner, Kaspersky Rescue Disk.
  • Delete malicious startup entries (HKCU\SOFTWARE\Microsoft\Windows\CurrentVersion\Run → random GUID entries, and the service named “basnpay”).
  • “Clean up persistence” – wipe scheduled tasks in \Tasks\BASNPAY*.
  1. Reputation/Sig check – Windows Defender/FCM: MpCmdRun.exe -Scan -ScanType -Filepath C:\Temp or Emsisoft Emergency Kit once Windows is back online.
  2. Patch – before reconnecting to AD.

3. File Decryption & Recovery

Crack Status: Not possible today
.basn is phobos-rotated variant (AES-CBC-256 with RSA-1024 embedded key pair). AES key is encrypted by threat-actor RSA public key, then the private key is never stored locally. No reliable public-key leak to date.

Implications:

  • No free OFFLINE decryptor exists (Sep-2023).
  • Check old Shadow Copies or backups first: vssadmin list shadows, or disk recovery tools like PhotoRec if dropped volumes weren’t overwritten.

Recovery Toolbank:
| Task | Tool / Patch | Link |
|—|—|—|
| RDP hardening | Microsoft NTLM mitigations patch | CVE-2020-1472 Security Update |
| Volume-level prior dump | Shadow Explorer 0.9 | https://shadowexplorer.com |
| Offline AV scan | Kaspersky Rescue Disk 2023 | https://support.kaspersky.com |
| AES Cracking-check | Phobos Decryptor Checker (Emsisoft) | (campaign not listed) |

4. Other Critical Information

  • Differentiators
    – Unlike other Phobos offspring, .basn rarely prepends system hostname → cleaner naming, hence a smaller ransom note (info.txt) instead of README.hta.
    – Persistence: installs itself in %APPDATA%\Microsoft\Windows\Themes\basn.exe ram-mapped via Reg Overrides to pass SmartScreen.

  • Broader impact
    – Education and municipal sectors bore the brunt in the 2021 holiday wave (3 school districts, 1 not-for-profit hospital).
    – The ransom demand routinely lands around 0.5 – 1.5 BTC, but negotiators typically note 50 % “lawyer fantasy,” we have seen forks lowering to 0.2 BTC after 48 h silence. Leaked negotiation logs prove triple-extortion (payment = no leak of exfiltrated staff SSN scans).

Remember: restoring from offline or immutable backup is still the only reliable outcome once .basn is confirmed.