*.firex3m

[Content by Gemini 2.5]

The *.firex3m file extension signifies an infection by a variant of the STOP/Djvu ransomware family. This family is one of the most prolific and active ransomware threats, constantly releasing new variants with different file extensions. Understanding its modus operandi is crucial for effective prevention and recovery.

Technical Breakdown:

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: Files encrypted by this ransomware will have the .firex3m extension appended to their original names.
  • Renaming Convention: The typical renaming pattern for *.firex3m (like other STOP/Djvu variants) is:
    [Original Filename].id-[unique_ID].[random_characters].[firex3m]
    For example, a file named document.docx might become document.docx.id-A1B2C3D4.firex3m.
    Sometimes the [random_characters] part is omitted, making it simply [Original Filename].id-[unique_ID].firex3m. The [unique_ID] is a hexadecimal string identifying the victim’s machine.

2. Detection & Outbreak Timeline

  • Approximate Start Date/Period: Variants using the .firex3m extension were first observed in early 2023, specifically around January-February 2023. As a member of the broader STOP/Djvu family, its lineage dates back to late 2017/early 2018, with continuous and rapid development of new extensions.

3. Primary Attack Vectors

The *.firex3m variant, like its predecessors in the STOP/Djvu family, primarily relies on the following propagation mechanisms:

  • Bundled Software & “Cracked” Applications: This is the most common infection vector. Users download and install software from untrusted sources (e.g., torrent sites, free software download sites, keygen activators, pirated game installers). The ransomware is discreetly bundled within these seemingly legitimate applications.
  • Fake Software Updates: Malicious websites or pop-ups prompt users to download fake updates for popular software (e.g., Flash Player, Java, web browsers), which in reality are installers for the ransomware.
  • Malspam/Phishing Campaigns: Although less frequent for Djvu compared to other ransomware families, general phishing emails containing malicious attachments (e.g., seemingly legitimate documents with embedded macros) or links to compromised websites can deliver the payload.
  • Adware Bundling: Some aggressive adware installers or browser hijackers might silently download and execute the ransomware payload as a secondary infection.
  • Exploitation (Less Common for Djvu): While not a primary method for STOP/Djvu, general ransomware propagation can also include:
    • Remote Desktop Protocol (RDP) Exploits: Brute-forcing weak RDP credentials to gain unauthorized access and manually deploy the ransomware.
    • Software Vulnerabilities: Exploiting unpatched vulnerabilities in operating systems or widely used applications (e.g., web servers, content management systems).

Remediation & Recovery Strategies:

1. Prevention

Proactive measures are the most effective defense against *.firex3m and other ransomware:

  • Regular Backups: Implement a robust 3-2-1 backup strategy (3 copies of data, on 2 different media, with 1 copy off-site/offline). Ensure backups are isolated from the network to prevent encryption.
  • Software Updates: Keep your operating system, web browsers, antivirus software, and all applications fully patched and updated. This closes security vulnerabilities that attackers might exploit.
  • Antivirus/Endpoint Detection & Response (EDR): Use reputable and up-to-date antivirus or EDR solutions with real-time protection.
  • Email Security & User Training: Be suspicious of unsolicited emails, especially those with attachments or links. Train users to recognize phishing attempts.
  • Strong Passwords & MFA: Implement strong, unique passwords for all accounts and enable Multi-Factor Authentication (MFA) wherever possible.
  • Network Segmentation: Divide your network into segments to limit the lateral movement of ransomware if an infection occurs.
  • Disable Unnecessary Services: Turn off services like RDP if not needed, or secure them with strong credentials and network-level access restrictions.
  • Application Whitelisting: Restrict software execution to only approved applications.

2. Removal

If infected, follow these steps to effectively remove *.firex3m:

  1. Isolate the Infected System: Immediately disconnect the infected computer from the network (unplug Ethernet cable, disable Wi-Fi). This prevents the ransomware from spreading to other devices.
  2. Identify and Terminate Processes:
    • Open Task Manager (Ctrl+Shift+Esc).
    • Look for suspicious processes that consume high CPU or memory. Ransomware processes often have random-looking names or names that mimic legitimate system processes.
    • End any identified malicious processes.
  3. Boot into Safe Mode: Restart the computer and boot into Safe Mode with Networking. This loads only essential services and drivers, preventing the ransomware from fully executing.
  4. Scan with Reputable Antimalware:
    • Download and run a full system scan with a reputable antivirus/antimalware program (e.g., Malwarebytes, Windows Defender, Bitdefender, ESET). Ensure the definitions are updated.
    • Multiple scans with different tools can sometimes be beneficial.
  5. Remove Persistence:
    • Check startup folders: %APPDATA%\Microsoft\Windows\Start Menu\Programs\Startup
    • Check Task Scheduler (taskschd.msc): Look for suspicious scheduled tasks that might re-launch the ransomware.
    • Check Registry Editor (regedit.exe): Navigate to HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Run and HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Run for suspicious entries.
    • Delete any identified malicious files or entries.
  6. Delete Ransom Note and Malicious Files: Locate and delete the ransom note (typically _readme.txt) and any other suspicious files or executables dropped by the ransomware (e.g., in %TEMP%, %APPDATA%).
  7. Reboot and Rescan: After cleanup, reboot the system normally and perform another full scan to ensure complete removal.

3. File Decryption & Recovery

  • Recovery Feasibility:

    • Yes, but with caveats: Decryption for STOP/Djvu variants like *.firex3m is possible in many cases, but depends on whether an online key or an offline key was used for encryption.
      • Online Key: If the ransomware successfully connected to its Command and Control (C2) server during encryption, it used a unique “online key” for your specific infection. Decryption with this key is currently only possible if you pay the ransom (which is not recommended) or if security researchers manage to obtain and publish these specific keys, which is rare.
      • Offline Key: If the ransomware failed to connect to its C2 server, it resorted to an “offline key” embedded within its code. This key is common to many victims, and researchers often manage to reverse-engineer and publish these keys, making decryption possible.
    • How to check: The personalid.txt file (or similar, sometimes contained within _readme.txt) or the ransomware’s executable will contain your unique ID. If the last 8 characters of your unique ID are t1 (e.g., id-A1B2C3D4t1), it likely indicates an offline key was used.

  • Methods/Tools Available:

    1. Emsisoft Decryptor for STOP/Djvu: This is the primary and most reliable tool for decrypting STOP/Djvu files.
      • Download the official tool from Emsisoft (often linked via No More Ransom! project).
      • The tool attempts to match your encrypted files against known online and offline keys. You need to provide at least one encrypted file and its original (unencrypted) version if possible, or some encrypted files.
      • Important: Decryption is not guaranteed. If an online key was used and is not known, the decryptor will fail.
    2. Shadow Volume Copies: Ransomware often attempts to delete Shadow Volume Copies (VSS snapshots) using vssadmin.exe. However, sometimes this command fails, or an older backup might survive.
      • Use tools like ShadowExplorer to check if any restore points or shadow copies exist. If they do, you might be able to recover older versions of your files.
    3. Data Recovery Software: For highly critical individual files, data recovery software (e.g., PhotoRec, Recuva) might be able to recover fragments of the original files if they were simply marked for deletion rather than securely overwritten after encryption. Success rates vary wildly.
    4. Backups: The most effective recovery method remains restoring from clean, isolated backups.

  • Essential Tools/Patches:

    • For Prevention: Robust Antivirus/EDR, a reliable backup solution, a secure password manager, and a patch management system.
    • For Remediation/Recovery: Emsisoft Decryptor for STOP/Djvu, Malwarebytes Anti-Malware, ShadowExplorer, and a clean installation media for your OS in case a full wipe and reinstall is necessary.

4. Other Critical Information

  • Additional Precautions:
    • Ransom Note (_readme.txt): Like other STOP/Djvu variants, *.firex3m typically drops a _readme.txt file in every folder containing encrypted files, and on the desktop. This file contains instructions on how to pay the ransom (usually $490, doubling to $980 if not paid within 72 hours) and contact information for the attackers (email addresses like [email protected] or [email protected]).
    • Host File Modification: The ransomware often modifies the Windows hosts file (C:\Windows\System32\drivers\etc\hosts) to block access to security-related websites (e.g., antivirus vendors, security blogs) to prevent victims from seeking help or downloading security tools. This file must be checked and restored to its original state.
    • Deletes Shadow Copies: It uses vssadmin.exe Delete Shadows /All /Quiet to prevent recovery from system restore points.
    • Persistence Mechanisms: It often creates scheduled tasks or modifies registry run keys to ensure it restarts upon system boot.
  • Broader Impact:
    • Widespread Disruption: Due to its common attack vectors (especially cracked software), STOP/Djvu variants like *.firex3m frequently impact individual users and small businesses, leading to significant data loss and operational downtime.
    • Financial Strain: Victims face the difficult choice of paying a ransom (with no guarantee of decryption) or losing their data. The costs associated with incident response, system remediation, and potential data recovery can be substantial.
    • Reputational Damage: For businesses, a ransomware attack can severely damage customer trust and brand reputation.
    • Evolutionary Threat: The STOP/Djvu family’s continuous development of new variants and extensions makes it a persistent and adaptable threat, requiring constant vigilance from the cybersecurity community.

By understanding these technical details and implementing the recommended strategies, individuals and organizations can significantly enhance their resilience against *.firex3m and similar ransomware attacks.