@gmx.de*

[Content by Gemini 2.5]

As a cybersecurity expert specializing in ransomware, I’ve compiled a detailed resource regarding the ransomware variant commonly identified by the file extension containing @gmx.de*. It’s crucial to understand that *@gmx.de* is typically part of the contact email address embedded within the appended file extension used by variants of the STOP/Djvu ransomware family. This family is one of the most prolific and constantly evolving ransomware threats, primarily targeting individual users and small businesses.

Technical Breakdown:

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: The exact file extension used by this ransomware family is not simply @gmx.de. Instead, gmx.de is a common email domain used by the attackers for contact, which is embedded within the full appended extension.

    • The complete encrypted file extension will typically follow the pattern: .[random_string].[contact_email_address].
    • For the variants using @gmx.de, this often looks like: .[random_string].gmx.de.
    • Example: A file named document.docx might become document.docx.mkos.[[email protected]]. While the prompt specifically mentions @gmx.de*, it’s important to clarify that the actual extension would be a unique 4-character string (e.g., .mado, .karl, .gero, .qall) followed by the contact email embedded, like document.docx.mado which, when opened, would lead to a ransom note containing the gmx.de email address. For the purpose of the prompt, we are referring to the group of variants that use gmx.de as their contact method.

  • Renaming Convention: The typical file renaming pattern is:
    OriginalFilename.OriginalExtension.[four_character_extension].{contact_email_domain}
    or more generally (as seen with Djvu):
    OriginalFilename.OriginalExtension.abcd (where abcd is the specific Djvu variant’s extension, and the ransom note then reveals the @gmx.de email).

    For example:

    • photo.jpg becomes photo.jpg.mkos
    • report.pdf becomes report.pdf.gero
      The ransom note (_readme.txt) will then contain instructions and the contact email, e.g., [email protected], [email protected], etc.

2. Detection & Outbreak Timeline

  • Approximate Start Date/Period: The STOP/Djvu ransomware family has been active since at least late 2017 / early 2018. It has seen numerous iterations and significant spikes in activity throughout 2019, 2020, 2021, and continues to be highly prevalent. Variants using @gmx.de as a contact method have been consistently observed since the early days of this family’s widespread distribution, evolving with the overall Djvu operation. New variants are released almost daily, making it a continuous threat.

3. Primary Attack Vectors

The STOP/Djvu ransomware, including variants using @gmx.de for contact, primarily employs the following propagation mechanisms:

  • Cracked Software/Pirated Content Downloads: This is the most common and effective method. Users seeking free versions of paid software (e.g., Adobe Photoshop, Microsoft Office, video games, system optimizers) download infected installers from torrent sites, unofficial software download portals, or shady forums. The ransomware is bundled with the “cracked” application or keygen.
  • Malicious Email Attachments & Phishing Campaigns: While less common than cracked software for initial Djvu infections, some variants are distributed via deceptive emails containing malicious attachments (e.g., seemingly legitimate invoices, shipping notifications, or resumes) that, when opened, execute the ransomware payload.
  • Fake Software Updates: Pop-ups or deceptive websites prompting users to “update” their Flash Player, browser, or other common software, which instead download and execute the ransomware.
  • Malvertising: Malicious advertisements on legitimate or illegitimate websites that redirect users to compromised sites or initiate drive-by downloads.
  • Web Injectors/Compromised Websites: Less frequent, but some instances involve the ransomware being injected directly into compromised websites, infecting visitors.
  • Remote Desktop Protocol (RDP) Exploits: While not a primary initial infection vector for the broad, untargeted distribution of Djvu, compromised RDP credentials can be used in targeted attacks to deploy various malware, including ransomware. However, Djvu typically relies on user execution rather than network exploitation for initial spread.

Remediation & Recovery Strategies:

1. Prevention

  • Proactive Measures:
    • Regular, Offline Backups: This is paramount. Maintain multiple copies of critical data on external drives or cloud services that are not continuously connected to your network. Test your backup restoration process regularly.
    • Robust Antivirus/Anti-Malware Solutions: Install and maintain reputable antivirus software with real-time protection. Ensure it’s always up-to-date.
    • Software and OS Updates: Keep your operating system (Windows, macOS) and all installed software (browsers, plugins, applications) fully patched and up-to-date. Attackers often exploit known vulnerabilities.
    • Email Security Awareness: Be extremely cautious with unsolicited emails, especially those with attachments or links. Verify the sender’s identity before clicking anything. Phishing awareness training is crucial.
    • Avoid Pirated Software: Never download or use cracked software, keygens, or activators from untrusted sources. These are primary vectors for Djvu.
    • Firewall Configuration: Ensure your firewall is active and configured to block unauthorized connections.
    • Disable Unnecessary Services: Turn off services like SMBv1, or RDP if not needed, or secure them with strong, unique passwords and multi-factor authentication if required.
    • User Account Control (UAC): Do not disable UAC on Windows, as it provides a layer of protection against unauthorized changes.
    • Ad Blockers: Use reputable ad blockers to mitigate malvertising risks.

2. Removal

  • Infection Cleanup:
    1. Isolate the Infected System: Immediately disconnect the infected computer from the network (unplug Ethernet cable, disable Wi-Fi) to prevent the ransomware from spreading (though Djvu primarily targets local files) or further compromising other systems.
    2. Identify and Terminate Malicious Processes: Use Task Manager (Ctrl+Shift+Esc) to look for suspicious processes. However, this can be difficult without expert knowledge.
    3. Boot into Safe Mode: Restart the computer in Safe Mode with Networking. This often prevents the ransomware from fully loading.
    4. Run a Full System Scan: Use your updated antivirus/anti-malware software (e.g., Malwarebytes, Windows Defender, ESET, Bitdefender) to perform a comprehensive scan. Allow the software to quarantine or remove all detected threats.
    5. Check Startup Programs and Scheduled Tasks: Open Task Manager -> Startup tab and msconfig -> Startup tab (for older Windows) or Task Scheduler and disable any suspicious entries.
    6. Review Hosts File: Check C:\Windows\System32\drivers\etc\hosts file for any malicious entries that redirect security websites. Remove any lines that don’t belong (default file is usually short, with mostly commented lines).
    7. Change All Passwords: After the system is deemed clean (or from an entirely separate, clean device), change all passwords for online accounts (email, banking, social media, cloud services) that were accessed from the compromised machine. This is critical as many Djvu variants drop information stealers before encrypting files.

3. File Decryption & Recovery

  • Recovery Feasibility:

    • General Rule: Decryption is extremely challenging for STOP/Djvu variants without the private key. Most modern Djvu variants use “online keys,” meaning a unique encryption key is generated for each victim and stored on the attackers’ server. This makes offline decryption attempts (without the attackers’ master key) impossible.
    • Emsisoft Decryptor: Emsisoft, in collaboration with security researchers, has developed a free decryptor for STOP/Djvu ransomware. This decryptor can successfully decrypt files for some offline key variants or older online key variants if the key has been recovered by researchers. It is not guaranteed to work for every single variant, especially the newest ones.
      • How it works: You submit an encrypted file and its original (unencrypted) counterpart (if available), or the decryptor tries to match the encrypted extension against known patterns. It checks if an “offline” key was used or if the “online” key is known.
      • Location: Search for “Emsisoft Decryptor for STOP Djvu” on their official website.
    • Backups: The most reliable method of recovery is restoring from clean, offline backups.
    • Shadow Volume Copies (VSS): Many ransomware variants, including Djvu, attempt to delete Shadow Volume Copies. However, it’s worth checking if they survive using tools like vssadmin or dedicated recovery software, although success rates are low.
    • Data Recovery Software: In some cases, if the original file was not completely overwritten (e.g., if only a portion was encrypted or the encryption process was interrupted), data recovery software (like PhotoRec, Recuva, etc.) might be able to recover older, unencrypted versions of files. This is a long shot but can sometimes salvage critical data.

  • Essential Tools/Patches:

    • Emsisoft Decryptor for STOP Djvu: The primary tool for potential decryption.
    • Reputable Anti-Malware Software: Malwarebytes, Windows Defender, ESET, Bitdefender, etc., for removal.
    • Windows Updates: Ensure your OS is fully patched to protect against system vulnerabilities.
    • Backup Solutions: Tools for automated or manual backups (e.g., external HDDs, cloud services like OneDrive, Google Drive, Backblaze).
    • Password Manager: To generate and store strong, unique passwords after cleaning.

4. Other Critical Information

  • Additional Precautions:

    • Information Stealer Component: A crucial and often overlooked aspect of STOP/Djvu ransomware is that many (if not most) variants first deploy an information-stealing malware (e.g., Vidar Stealer, Azorult, RedLine Stealer) before file encryption. This stealer collects browser histories, cached passwords, cryptocurrency wallet data, cookies, and other sensitive information. Therefore, changing all passwords from a clean device after the infection is mitigated is absolutely vital.
    • Ransom Note: The ransomware typically drops a text file named _readme.txt in every encrypted folder and on the desktop. This file contains instructions on how to pay the ransom (usually in Bitcoin), the contact email address (e.g., [email protected]), and the amount demanded. The ransom typically doubles after a few days.
    • No Guarantee of Decryption After Payment: Even if you pay the ransom, there is no guarantee that the attackers will provide a working decryption key or tool. Cybersecurity experts universally advise against paying ransoms.
    • Offline vs. Online Keys: Be aware that the decryptor’s success largely depends on whether your files were encrypted with an “offline key” (which is rare for newer Djvu variants) or an “online key.” The decryptor will indicate which type was used.

  • Broader Impact:

    • Widespread Financial Loss: Due to its low barrier to entry for attackers (distributing cracked software is relatively easy) and its targeting of individual users and small businesses, Djvu has caused billions in financial losses globally through direct ransom payments and data loss.
    • Data Loss and Disruption: For victims without adequate backups, the loss of personal photos, documents, and critical business files can be catastrophic.
    • Identity Theft and Account Compromise: The accompanying information-stealing malware significantly increases the risk of identity theft, financial fraud, and compromise of online accounts.
    • Constant Evolution: The rapid release of new variants by the operators makes it challenging for security researchers to develop universal decryptors, leading to a continuous cat-and-mouse game.

By understanding these technical details and implementing robust prevention and recovery strategies, individuals and organizations can significantly reduce their risk and mitigate the impact of ransomware like the @gmx.de variants of STOP/Djvu.