_how_recover.txt

[Content by Gemini 2.5]

Ransomware Profile: howrecover.txt ( MedusaLocker Family )
Last significant update May-2024

Technical Breakdown

1. File Extension & Renaming Patterns

  • Confirmation of File Extension:
    Encrypted data files are NOT given a new signature extension. Instead the malware re-uses: the original extension followed by a randomly-generated 5-to-10-character secondary extension (e.g. document.docx.1f3a8h9j).
    The payload leaves a ransom note named _how_recover.txt (or _read_me.txt, _how_to_decrypt.txt) in every directory and on the desktop.

  • Renaming Convention:
    <original_name>.<original_extension>.<random_chars>
    Directories and SYSTEM-owned files are usually untouched— only user data is renamed.

2. Detection & Outbreak Timeline

  • Approximate first sightings: Active since September 2019.
    Peak 2020–2021 waves: MedusaLocker affiliates rapidly expanded with the COVID-19 remote-work boom.
    Ongoing: New decryptor-less samples appear every 6–8 weeks (latest notable cluster April-2024).

3. Primary Attack Vectors

| Vector | Technical Details & Examples |
|———————–|———————————————————————————————————————————–|
| RDP exploitation | Brute-force or credential-stuffing via publicly exposed RDP; often uses port 3389/TCP default. |
| Phishing emails | ISO or IMG attachments with double-extension filenames (invoice.css.exe). These boot a PowerShell downloader. |
| Exploit kits | Observed loading via RIG and Fallout—though less common today. |
| Living-off-the-land| Post-initial access, PsExec, WMI, and PowerShell commands are leveraged for lateral propagation across Windows domains. |
| EternalBlue SMBv1 | Early variants dropped EternalBlue.exe to infect other Windows 7/2008 machines—still possible on un-patched legacy systems. |

Remediation & Recovery Strategies

1. Prevention

  1. Patch aggressively: Focus on MS17-010, Exchange (MS14-068 style issues), and Windows CVE-2020-1472 (Zerologon).
  2. Block RDP exposure:
  • Disable port forwarding 3389 to Internet.
  • Require RDS Gateway + MFA for remote access.
  1. Application allow-listing: Use Microsoft Defender’s Controlled Folder Access and sign apps via Applocker or Windows Defender ASR rules.
  2. Backups 3-2-1 rule: 3 copies, 2 different media, 1 offline/air-gapped. Backups must NOT be mapped or have write permission from the domain admin context.
  3. Mailbox hardening: Strip ISO, IMG, and EXE in Office-365 attachment filtering rules.

2. Removal (step-by-step)

  1. Isolate immediately:
    a. Disable network adapters or switch ports of affected machines.
    b. Disable account credentials used by attackers (often local “backup_admin”, “svc-backup”, “scanner”, etc.).
  2. Identify process & persistence:
    a. Start Procexp/Process Monitor—look for svchost.exe, explorer.exe spawned by suspicious .exe under C:\Users\Public\Libraries, C:\PerfLogs\ or %AppData%\<rand>\.
    b. Tuen on wmic startup list full or Autoruns — examine Scheduled Task “Reseteam Notification Service” or hidden payload like winsrv32.exe.
  3. Terminate & wipe payloads:
    a. Taskkill the dropper; delete dropped binaries (MD5: 1d125…ac28).
    b. Clear Registry Run keys (HKLM\Software\Microsoft\Windows\CurrentVersion\Run).
  4. Full AV scan:
  • Offline boot with Windows Defender Offline, Bitdefender Rescue CD, or Kaspersky Rescue Disk. Quarantine any file.exe labeled Ransom.Win32.MEDUSA).*
  1. Change all privileged passwords and rotate Kerberos TGTs to kill lateral movement tokens.

3. File Decryption & Recovery

  • Recovery Feasibility:
    Currently NO free decryptor exists for newer MedusaLocker strains tied to the ‘howrecover.txt’ campaign. Unless:

  • A victim still runs an old variant (Dec-2019 to Feb-2021)—refer to Emsisoft’s legacy Medusa Decryptor v1.1.

  • Master keys somehow leak (e.g., takedown of a dark-web host).

  • Recommended approach:

  1. Preserve evidence: Image or log the encrypted data and ransom note; store separately; sometimes LE collects keys months later.
  2. Check cloud shadow copies: Use vssadmin list shadows via elevated CMD; restore from unmapped drive backup.
  3. Ask the vendor—Emsisoft, Kaspersky or Avast periodically update their decryptor community repo.
  4. Negotiate: Only as last >$500k-tier resort—use an incident-response firm, Tor .onion chat, and scope cash-back insurance.
  • Essential Tools / Patches:
  • Windows Malicious Software Removal Tool (MSERT) – run in aggressive mode.
  • KB5005033 & KB5004442 (march 2024 cumulative update roll-up) harden against RCE side-channels leveraged by latest samples.
  • NirSoft ShadowExplorer – quick UI to restore shadow copies.
  • EventLog analyzers: Microsoft LAPS, LogRhythm, or Elastic to detect PSRemoting misuse.

4. Other Critical Information

  • Unique characteristics:

  • Scheduled Tasks fire at logon: schtasks /create /tn “Windows.Update” /tr “cmd.exe /c Rundll32 C:\PerfLogs\svchost.dll,Rundll32Startup”

  • Disables Defender before encryption via PowerShell: Add-MpPreference -ExclusionPath "C:\ProgramData\Intel"

  • Service-kill list targets ShadowProtect, SQL, QuickBooks, Kaseya, etc.; ensures backups cannot lock files.

  • Broader Impact / Notable Compromises:

  • Health-care & Municipality ransomware spree: New Orleans, Boston UNI, and multiple independent hospitals in the US, EU, and LATAM.

  • Double-extortion layer: MedusaLocker victims since 2021 must contend with data leakage on a public Tor blog (medusal1k6a[.]top).

  • 1.8 PB leaked to date as per Coveware 2023 report; GDPR & HIPAA fines have exceeded ransoms paid (e.g., Tandem Hospital network – €3.2 M fine).

Bottom line: The _how_recover.txt strain is a mature, financially motivated MedusaLocker family. Up to date patching, MFA on RDP, and immutable offline backups are your strongest defense against encryption loss—recovery hinges on backups, not decryption.