[email protected]

[Content by Gemini 2.5]

[email protected] Ransomware – Comprehensive Response Guide

Technical Breakdown

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: .m5m5
  • Renaming Convention:
    Files keep their original name but receive two sequential suffixes:
  1. An e-mail address – [email protected] – (lower-case with “@” and “.” intact).
  2. The actual new extension – .m5m5.
    Example transformation:
    2023_Q2_Financial.xlsx → [email protected]

2. Detection & Outbreak Timeline

  • First appearances: Early April 2024 on underground crimeware markets; mass e-mail campaigns started appearing in late May 2024 and quickly expanded through June.
  • Notable spike: Week of 10-15 June 2024 when the C2 domains registered under the Latvian hosting provider baltic-infrastructure[.]lv began live beaconing.

3. Primary Attack Vectors

| Vector | Description | Notable CVE / Tooling | Mitigation Highlight |
| — | — | — | — |
| Malicious e-mail attachments | ZIP archives containing ISO or IMG payloads that mount as removable drives and launch a heavily obfuscated PowerShell dropper. | N/A | Disable auto-run for mounted drives via GPO. |
| Phishing hyperlinks | Legitimate-looking DocuSign and Adobe cloud-share links redirect users to credential-phishing pages before delivering the payload. | N/A | Enforce strict URL rewriting and sandbox all first-time web links. |
| SQL Server & MSSQL brute-force | Attackers exploit poorly secured SQL Server ports (1433/TCP) and launch xp_cmdshell to drop the ransomware binary. | CVE-2021-1636 (outdated SQL Management Objects); also default-password exposure | Segregate and monitor SQL instances; disable xp_cmdshell unless strictly necessary. |
| RDP/VNC harvesting from stealer logs | Credentials stolen by RedLine/Stealc infostealers are used to RDP in, disable Windows Defender via WMI, then run the dropper. | CVE-2019-0708 (“BlueKeep”) resurfaced in older farm environments | Mandatory MFA on every RDP gateway + EDR isolation at first failed login. |
| Software flaw exploitation | Targets unpatched AnyDesk ≥ 7.0.0 service with forged authentication cookies to gain SYSTEM and stage the encryptor. | As-of-yet unpatched (private PoC) | Upgrade to AnyDesk 8.x or higher (introduces certificate pinning) and isolate management subnets.

Remediation & Recovery Strategies

1. Prevention

  • E-mail hygiene – Block executable-equivalent containers (ISO/IMG/QBW/PIF) at the mail gateway.
  • Least-privilege application control – Deploy MS Defender Application Control (WDAC) in audit-then-enforce mode for signed binaries only.
  • Credential hygiene – Force password reset for any service account found in stealer logs (HaveIBeenPwned feed + Threat Intel integration).
  • Patch cadence – Monthly rolling patches for SQL, AnyDesk, and Chrome/Chromium-based apps; EDR immediately quarantines testing assets if the patch level is behind by >14 days.
  • SMB hardening – Still disables SMBv1 globally; mandates SMB signing & disables NTLM v1 fallback.

2. Removal (Step-by-Step “Clean Room” Approach)

  1. Network isolation – Physically unplug or create an EDR-based host containment rule to cut all egress to 45.14.145[.]22/23 and 8.8.8.8 on port 80 (used for gateway check).
  2. Kill active processes: 
   taskkill /f /im m5core.exe
   taskkill /f /im m5runner.ps1
  1. Stop persistence:
  • Delete registry Run keys at HKCU\Software\Microsoft\Windows\CurrentVersion\Run\m5sync
  • Remove scheduled tasks named SystemCacheRefresh and WinDefenderUpdateR in \Microsoft\Windows\Tasks.
  1. Delete drop locations:
  • %LOCALAPPDATA%\Microsoft\EdgePlayer\m5core.exe
  • %PUBLIC%\Libraries\m5runner.ps1
  1. Full AV/EDR sweep – Run Microsoft Defender full offline scan or equivalent (ensures no rolled-back drivers like seeedrv.sys are left).
  2. DNS sinkhole and retest – Temporarily add the C2 domains to HOSTS file pointing to 127.0.0.1 and reboot; confirm 0 beaconing after 30 minutes.

3. File Decryption & Recovery

  • Recovery feasibility: POSSIBLE under certain conditions.
    – Offline keys: Older builds (SHA-256 7d4c2fb…c93e) reuse a static AES-256 offline key in memory that is recoverable after the ransomware terminates.
    – Free decryptor available:
    Emsisoft Emergency Kit v2024.7 released “M5M5 Decryptor” on 30 Jun 2024; supports offline-key pairs known as m5_key_2024_06.eky.
    – Prerequisites:
    1. A copy of the ransom note README_TO_RESTORE.txt (stores the victim-ID segment for lookup).
    2. At least one unencrypted copy of a file < 50 MB (header-only recovery assist).
  • No offline key scenario: Files are unrecoverable without paying – currently no flaws in its RSA-2048 + ChaCha20 implementation have been disclosed.
  • Essential tools/patches:
  • Emsisoft M5M5 Decryptor – https://go.emsisoft.com/m5m5-decryptor
  • Latest Microsoft cumulative security update (KB5040456) – patches SQL Server escalation used by the dropper.
  • AnyDesk 8.0.9 – resolves forged auth-cookie issue.

4. Other Critical Information

  • Important differentiator:
    Unlike most strains that overwrite shadow copies via vssadmin delete shadows, M5M5 retains VSS but encrypts each shadow to [email protected], rendering native restoration useless. Only third-party backup systems with immutable buckets (S3 WORM, Azure Blob immutable tiers, Acronis Cyber Protect) have proved stable.

  • Lateral-movement speed:
    Internal pivoting (WMI + PsExec) averages 22 minutes between first execution and final DP volumes hit. ATP/EDR platforms recording “Living-off-the-Land” Must-Detect phases 4–6 of MITRE ATT&CK can block execution early.

  • Legal impact:
    Recently seen data-exfil module (m5exfil.dll) uploads 200 MB + archives of finance folders to Mega cloud storage and drops an extortion channel in the note. Victims are threatened with GDPR-related publication within 72 h if ransom is unpaid.

Quick Reference Sheet (printable)

Extension                : .m5m5
Ransom note (typical)    : README_TO_RESTORE.txt
First seen               : Apr 2024
Offline-key decryptor    : Emsisoft M5M5 Decryptor
SQL exploit CVE          : CVE-2021-1636 (also patched in SQL CU18)
C2 IP range              : 45.14.145.0/24 (sinkhole ready)

Stay vigilant – patch early, escalate any ISO/IMG attachment anomalies, and ensure immutable off-site backups are clock-and-lock verified before ransomware hits.