Technical Breakdown of the “contactheretorecoveryour_files.txt” Ransomware Family
(confirmed alias of the MedusaLocker strain, 2023–2024 wave)
1. File Extension & Renaming Patterns
-
Exact extension appended:
Victim-specific four-to-six character random strings such as.skynet
,.soviet
,.bombe
,.lockbit2
,.encrypted
(NOT a single static extension; each campaign varies). -
Renaming convention applied before the extension:
[original_filename][random_no]@[email_address].<extension>
Example:
budget-Q1.xlsx
→budget-Q1.xlsx.[B30EC321][[email protected]].soviet
The e-mail in the filename is drawn from pools hard-coded in each build:
[email protected]
,[email protected]
,[email protected]
, etc.
Concurrently, inside every encrypted folder the script dropsHOW_TO_RECOVER_FILES.txt
(a.k.a.contact_here_to_recover_your_files.txt
).
2. Detection & Outbreak Timeline
- First sightings: October 2019 (MedusaLocker v1).
- Major resurgence with new builds using “contactheretorecoveryour_files.txt”:
- Campaign-1: Mid-June 2023 (primarily English/US orgs)
- Campaign-2: Late-Jan 2024 (targeted APAC manufacturing)
-
Current-gen detections:
Most vendors now label it MedusaLocker-2024 (sometimes tracked as “LockerGoga-Medusa blend”) and update sigs continuously.
3. Primary Attack Vectors
- Initial foothold:
- RDP brute-force / credential stuffing (port 3389/TCP, default or weak credentials).
- Phishing e-mails with macro-enabled Office documents containing WScript PowerShell loaders.
- Adversary-in-the-middle (AitM) Phishing kits (Evilginx-style) to harvest O365 creds → RDP pivot.
- Exploit kits leveraging an unpatched Exchange ProxyShell (CVE-2021-34473, CVE-2021-34523) on public-facing mail servers.
- Privilege escalation & propagation:
- Uses EternalBlue exploit (ms17-010) and SMBv1 NTLM relay if it finds legacy hosts behind the breached perimeter.
- Leverages WMI + PSExec once the payload lands on a single domain controller for ransomware-wide domain push.
Remediation & Recovery Strategies
1. Prevention Checklist
| Control | Rationale / Config Notes | MVP Actions |
|————————————|————————–|————-|
| MFA for ALL remote-access vectors | Blocks initial MalAuth to RDP & VPN | Enable AD FS / Azure AD MFA, disable legacy NTLM |
| Push Windows cumulative updates | Eliminates EternalBlue, Zerologon (CVE-2020-1472), etc. | Approve May 2023 CU or newer |
| Segment networks via VLAN / ACL | Limits lateral SMB movement | Isolate critical ERP and file shares |
| Disable SMBv1 via GPO / registry | Removes SMBv1 propagation vector | Disable-Smb1Protocol -Force
|
| Harden RDP: NLA, TLS 1.2+, TSA | Blocks credential stuffing and MitM | Enforce in Group Policy |
| Phishing-resistant MFA + EDR hooks | Stops macro-based loaders | Enable Microsoft 365 default blocks for macro webmkt |
| Principle of least privilege | Reduces domain-wide cluster damage | Remove local Admin from regular users |
2. Step-by-Step Infection Cleanup
- Immediately isolate affected machines (pull network, disable Wi-Fi/Bluetooth).
- Collect evidence (full MFT + OS memory; store on write-protected SSD).
- Boot into Safe Mode with Networking for cleaning machines used to plan recovery (use a trusted, read-only WinRE USB).
-
Run current-generation AV/EDR (SentinelOne, ESET, Bitdefender, Sophos) → signature
Win32/Filecoder.Medusa.*
updated since May-2024. - Purge persistence:
- Delete scheduled task
\Microsoft\Windows\
named random GUID (e.g.,{E4514C89-BFFB-B43B}
). - Remove Registry “Run” key at
HKCU\Software\Microsoft\Windows\CurrentVersion\Run
(“vpndata”).
- Patch or rebuild any compromised domain controllers.
-
Validate safe mode boot sectors; MedusaLocker v2024 drops a hidden EFI driver (
Usbxhci.efi
) as a boot-kit to re-launch after Safe Boot. Use EDR-rescue media → Delete the file.
3. File Decryption & Recovery
- No public decryption tool has broken MedusaLocker-2024 AES-256 + RSA-2048 hybrid encryption.
-
Recovery is ONLY possible if you:
a. Possess an offline backup that was air-gapped or
b. Hold the master private key leaked/stolen from previous operator (none released to date). -
Recommended actions:
✅ Restore from clean backups via the 3-2-1 rule.
✅ Test decrypt sample before mass-restore to ensure backup integrity.
❌ Do NOT pay—payment does not guarantee a decryptor; Medusa operators frequently provide broken keys or vanish.
4. Other Critical Information
-
Double-extortion model: operators exfiltrate “company_data\” via MEGA API and threaten publication on dark-web leak site (
hxxp://medusalockerfkscxf.onion
). -
Unique change from earlier vectors: v2024 variant steals BitLocker keys from TPM via
iBFT ACPI table
, allowing attackers to re-spread to encrypted laptops even after full disk reset. -
Notable incidents
2023-11: Tier-1 Japanese automotive supplier lost 1.2 TB of design IP—recovery cost > US $45 M.
2024-03: European container terminal suffered $15 M revenue loss from 7-day outage.
Succinct Cheat-Sheet (Print & Pin)
1 DETECTION sign – vЮ.pkg or “contact_here/ recover files/ .txt” note
2 ISOLATE – pull network cables, phone SOC NOW
3 BACKUP – confirm 3-2-1 restore point verified offline
4 PATCH – roll May-2024 cumulative & Exchange KB5034441
5 NO PAY – extortion gang historically unreliable
Stay safe—patch early, back up often, and share IOCs with your threat-sharing community.