@bigmir.net

[Content by Gemini 2.5]

This resource provides a comprehensive overview of the ransomware variant identified by the file extension @bigmir.net, a type commonly associated with the Dharma (also known as Phobos) ransomware family. This analysis includes its technical characteristics and actionable recovery strategies.

Technical Breakdown:

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: Files encrypted by this ransomware typically have an additional extension appended to their original name, which includes a unique victim ID and the attacker’s email address. For the @bigmir.net variant, the appended extension will generally follow the pattern:
    .id-[random_hexadecimal_string].bigmir.net
    Sometimes, the original file extension is also preserved or added again at the end, but the distinguishing characteristic is the unique ID followed by the @bigmir.net email address.

  • Renaming Convention:
    A file originally named document.docx might be renamed to:
    document.docx.id-A1B2C3D4.bigmir.net
    The [random_hexadecimal_string] (e.g., A1B2C3D4) is a unique identifier generated for each victim. This pattern is consistent with Dharma/Phobos variants, which often use email addresses (like @bigmir.net, @aol.com, @gmail.com, etc.) as part of the encrypted file extension.

2. Detection & Outbreak Timeline

  • Approximate Start Date/Period: The Dharma ransomware family, which this @bigmir.net variant belongs to, first emerged around 2016-2017. It has continuously evolved, with new variants and associated email addresses appearing regularly. The @bigmir.net specific variant is one of many email addresses used by Dharma/Phobos operators over the years, indicating a sustained and ongoing threat from this family. Its prevalence has ebbed and flowed but remains a persistent threat, particularly against small to medium-sized businesses (SMBs).

3. Primary Attack Vectors

  • Propagation Mechanisms: @bigmir.net (and other Dharma/Phobos variants) primarily relies on the following methods to infiltrate systems:
    • Remote Desktop Protocol (RDP) Exploitation: This is the most common attack vector. Threat actors often scan the internet for open RDP ports, then use brute-force attacks or stolen credentials (credential stuffing) to gain unauthorized access. Once inside, they manually deploy the ransomware.
    • Phishing Campaigns: Malicious emails containing weaponized attachments (e.g., seemingly legitimate documents with embedded macros, or archives containing executable files) or links to compromised websites are also used. If the user executes the payload, the ransomware is installed.
    • Software Vulnerabilities: While less common than RDP exploitation for initial access, attackers may exploit known vulnerabilities in unpatched software (e.g., VPNs, web servers, or other exposed services) to gain a foothold in the network.
    • Weak Passwords & Exposed Services: Any service accessible from the internet with weak or default credentials (e.g., SMB shares, VPNs, databases) can be a target for direct compromise, leading to ransomware deployment.
    • Third-Party Software/Supply Chain: Compromise of legitimate software updates or third-party tools can also serve as an infection vector, though this is less frequent than RDP.

Remediation & Recovery Strategies:

1. Prevention

  • Proactive Measures:
    • Strong Password Policies & Multi-Factor Authentication (MFA): Enforce complex, unique passwords for all accounts, especially those with administrative privileges or RDP access. Implement MFA wherever possible, especially for remote access services.
    • RDP Hardening: Limit RDP access to trusted IP addresses using firewalls. Put RDP behind a VPN. Use Network Level Authentication (NLA). Monitor RDP logs for unusual activity.
    • Regular Backups (3-2-1 Rule): Implement a robust backup strategy: at least three copies of your data, stored on two different media types, with one copy off-site or air-gapped (offline) to protect against encryption. Test your backups regularly for integrity and restorability.
    • Patch Management: Keep all operating systems, applications, and network devices fully updated with the latest security patches. Prioritize patches for known vulnerabilities.
    • Endpoint Detection and Response (EDR) / Antivirus (AV): Deploy reputable, up-to-date EDR or AV solutions on all endpoints and servers. Configure them for real-time protection and regular scans.
    • Network Segmentation: Segment your network to limit lateral movement if a system becomes compromised.
    • Security Awareness Training: Educate employees about phishing, suspicious emails, and safe browsing habits.
    • Disable Unnecessary Services: Turn off any services or protocols that are not essential for business operations (e.g., SMBv1, unnecessary RDP access).

2. Removal

  • Infection Cleanup:
    1. Isolate Infected Systems: Immediately disconnect any compromised systems from the network (physically or by disabling network adapters) to prevent further spread.
    2. Identify and Contain: Determine the extent of the infection. Scan other systems on the network.
    3. Terminate Malicious Processes: Use Task Manager, Process Explorer, or taskkill commands to terminate any suspicious processes, particularly those running from unusual locations or with high CPU/disk usage.
    4. Remove Ransomware Executables:
      • Boot the infected system into Safe Mode or use a live bootable anti-malware disk.
      • Use a reputable and up-to-date anti-malware solution to scan and remove the ransomware executable files and any associated dropped files. Common locations for ransomware executables include AppData, ProgramData, Temp folders, or Windows system directories.
      • Manually check common persistence locations (Registry Run keys, Startup folders, Scheduled Tasks) and remove any entries related to the ransomware.
    5. Restore System: If you have a clean system image or a known good restore point from before the infection, consider restoring the operating system.
    6. Change Credentials: After ensuring the system is clean, immediately change all passwords, especially for administrative accounts and any accounts potentially compromised during the RDP breach.

3. File Decryption & Recovery

  • Recovery Feasibility: For the vast majority of current Dharma/Phobos variants, including those using @bigmir.net, there is no publicly available free decryption tool. The encryption used is strong (typically AES-256 combined with RSA-2048), and without the attacker’s private key, decryption is virtually impossible.
    • Paying the Ransom: Paying the ransom is strongly discouraged. There is no guarantee you will receive a decryptor, and even if you do, it may not work perfectly, and you are funding criminal activity.
    • No More Ransom Project: While No More Ransom (nomoreransom.org) is an excellent resource for many ransomware variants, it is unlikely to have a decryptor for live Dharma/Phobos variants, though it’s always worth checking for updates.
  • Essential Tools/Patches:
    • Backups: This is the most critical tool for recovery. If you have valid, unencrypted backups, you can restore your files and systems.
    • Data Recovery Software: In some rare cases, if the ransomware merely overwrote files rather than encrypting them directly (less common with Dharma), data recovery software might retrieve previous versions, but this is highly unlikely for encrypted files.
    • Volume Shadow Copies: Dharma/Phobos variants are known to delete Volume Shadow Copies (using commands like vssadmin delete shadows /all /quiet). However, it’s always worth checking if any remain, as they can sometimes allow recovery of previous file versions. Use vssadmin list shadows from an elevated command prompt.
    • Reputable Anti-malware / EDR Solutions: For removal and ongoing protection.
    • System and Application Updates: To patch vulnerabilities that could be exploited.

4. Other Critical Information

  • Additional Precautions:
    • Persistence Mechanisms: Dharma/Phobos often creates entries in the Registry’s Run keys, drops itself into Startup folders, or creates Scheduled Tasks to ensure it restarts with the system.
    • Shadow Copy Deletion: As mentioned, it commonly attempts to delete shadow copies to prevent easy file recovery.
    • UAC Bypass: Some variants employ techniques to bypass User Account Control (UAC) to execute with elevated privileges.
    • Ransom Note: The ransomware typically drops text files named FILES ENCRYPTED.txt, info.txt, or similar, and sometimes creates a desktop wallpaper change. These notes contain instructions on how to contact the attackers (usually via email, hence the @bigmir.net in the file extension) and the ransom demand.
  • Broader Impact:
    • Data Loss: The primary and most severe impact is the irreversible loss of encrypted data if no viable backups are available and decryption is not possible.
    • Operational Disruption: Significant downtime for businesses, leading to lost productivity, revenue, and potential reputational damage.
    • Financial Costs: Beyond potential ransom payments (which are not recommended), there are significant costs associated with incident response, system rebuilding, data recovery efforts, and potential legal/compliance repercussions.
    • Supply Chain Risk: If an organization within a supply chain is infected, it can have ripple effects on partners and customers.

By understanding these technical details and implementing the recommended prevention and recovery strategies, individuals and organizations can significantly reduce their risk and improve their resilience against the @bigmir.net ransomware variant and similar threats.