*.*.dewar

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This document provides a comprehensive overview and remediation strategies for the ransomware variant identified by the file extension *.*.dewar. This variant is part of the prolific and continuously evolving STOP/Djvu ransomware family.

Technical Breakdown:

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: The exact file extension used by this ransomware variant is .dewar. This means a file like document.docx would be renamed to document.docx.dewar.
  • Renaming Convention: The typical file renaming pattern employed by the .dewar variant (and the broader STOP/Djvu family) is:
    [original_filename].[original_extension].dewar
    For example:
    • photo.jpg becomes photo.jpg.dewar
    • report.pdf becomes report.pdf.dewar
    • archive.zip becomes archive.zip.dewar
      In addition to file encryption, the ransomware typically drops a ransom note named _readme.txt in every folder containing encrypted files, and often on the desktop.

2. Detection & Outbreak Timeline

  • Approximate Start Date/Period: The STOP/Djvu ransomware family, to which the .dewar variant belongs, has been highly active since at least late 2018. New variants (identifiable by their unique file extensions) are released almost daily, making it one of the most persistent and widespread consumer-targeted ransomware threats. The .dewar extension itself would have emerged as one of these many daily or weekly new variants.

3. Primary Attack Vectors

The STOP/Djvu ransomware typically leverages social engineering and less sophisticated technical exploits to propagate. Its main methods include:

  • Software Cracks/Keygens: This is the most prevalent method. Users download seemingly legitimate cracked software, key generators, or activators from unofficial websites (e.g., torrent sites, free software download sites), which are bundled with the ransomware.
  • Fake Software Updates: Malicious websites or pop-ups prompt users to download fake updates for popular software (e.g., Adobe Flash Player, web browsers, media players), which are actually ransomware installers.
  • Malicious Advertisements (Malvertising): Compromised ad networks or websites display malicious advertisements that redirect users to pages hosting exploit kits or directly download malware.
  • Phishing Campaigns: While less common for Djvu compared to corporate-focused ransomware, basic phishing emails containing malicious attachments (e.g., seemingly legitimate documents with embedded macros) or links to malware download sites can also be used.
  • Remote Desktop Protocol (RDP) Exploits: While not a primary vector for Djvu, poorly secured RDP endpoints can be brute-forced or compromised, allowing attackers to manually install the ransomware.
  • Software Vulnerabilities: Less common for Djvu, but any unpatched software vulnerability, especially in web browsers, media players, or operating systems, could potentially be exploited to deliver the payload.

Remediation & Recovery Strategies:

1. Prevention

  • Proactive Measures:
    1. Regular Backups: Implement a robust 3-2-1 backup strategy (3 copies of data, on 2 different media, with 1 copy off-site/offline). This is the single most important defense against data loss from ransomware.
    2. Use Reputable Antivirus/Anti-Malware: Install and keep updated a comprehensive security suite with real-time protection and behavioral analysis capabilities.
    3. Software Updates & Patching: Keep your operating system, web browsers, and all installed software up-to-date with the latest security patches. Many ransomware attacks exploit known vulnerabilities.
    4. Practice Email Security: Be wary of unsolicited emails, especially those with attachments or links. Verify the sender before opening anything.
    5. Educate Users: Train users to identify phishing attempts, avoid downloading cracked software, and be cautious about clicking suspicious links or advertisements.
    6. Disable Unnecessary Services: Disable RDP if not needed, or secure it with strong passwords, multi-factor authentication (MFA), and network-level authentication (NLA).
    7. Firewall Configuration: Use a firewall to block suspicious incoming and outgoing connections.

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 further spread.
    2. Identify the Threat: Use a reputable antivirus/anti-malware scanner (e.g., Malwarebytes, Emsisoft Emergency Kit, Avast, Kaspersky) to scan the entire system and identify all malicious files associated with the .dewar ransomware.
    3. Remove Identified Malware: Follow the instructions of your security software to quarantine and remove the detected threats. You might need to boot into Safe Mode with Networking to run the scan effectively, as the ransomware might try to block security tools.
    4. Check for Other Malware: STOP/Djvu ransomware is notorious for often installing additional malware, such as information stealers (e.g., Vidar, Azorult, RedLine Stealer). Run additional scans with different tools to ensure no other malicious payloads remain.
    5. Change Passwords: After confirming the system is clean, change all passwords used on the infected machine, especially for online accounts (email, banking, social media), as information stealers may have compromised them.

3. File Decryption & Recovery

  • Recovery Feasibility: The feasibility of decrypting files encrypted by the .dewar variant of STOP/Djvu ransomware without paying the ransom is limited and highly dependent on the encryption key type used during the infection.
    • Online Keys (Most Common): The majority of STOP/Djvu infections use unique “online keys” generated on the attacker’s server for each victim. If an online key was used, free decryption is currently not possible unless the attackers decide to release the master decryption keys or a significant flaw is found in their encryption scheme. Paying the ransom is strongly discouraged as there’s no guarantee of decryption and it fuels further criminal activity.
    • Offline Keys (Less Common): In rare cases, if the ransomware couldn’t connect to its command-and-control server, it might use a static “offline key.” If an offline key was used, there is a possibility of decryption using tools like the Emsisoft STOP Djvu Decryptor. This tool works by attempting to match encrypted files with known offline keys discovered by researchers.
  • Methods/Tools Available:
    1. Emsisoft STOP Djvu Decryptor: This is the primary tool for potential decryption of STOP/Djvu variants. Users need to download it and follow its instructions, providing an encrypted file and its original (unencrypted) counterpart if available, to help the tool identify the correct key.
    2. System Restore Points/Volume Shadow Copies: In some cases, if the ransomware failed to delete them (which it usually attempts to do), you might be able to recover previous versions of your files using System Restore Points or Volume Shadow Copies. However, this is often a long shot for Djvu infections.
    3. Data Recovery Software: Tools like PhotoRec or Recuva might be able to recover older, deleted versions of files if they haven’t been overwritten. This is distinct from decryption and only works if the original files were deleted rather than truly encrypted in place.
    4. Restoring from Backups: The most reliable and recommended method for file recovery is to restore your data from clean, verified backups.

4. Other Critical Information

  • Additional Precautions (Unique Characteristics):
    • Information Stealer Payload: A critical characteristic of the STOP/Djvu family, including the .dewar variant, is its tendency to drop additional malware, most commonly information stealers (e.g., Vidar, Azorult, RedLine Stealer). These stealers aim to exfiltrate sensitive data such as browser histories, cryptocurrency wallets, saved passwords, and system information. Therefore, a successful infection cleanup must include thorough scanning for and removal of these secondary payloads, and changing all potentially compromised passwords.
    • High Volume and Constant Evolution: This family is highly active, with new variants and extensions released frequently, making it a persistent threat to individual users. This constant evolution means that decryption tools must also be continually updated, and older tools may not work for newer variants.
    • Offline Key Complexity: Determining if an offline key was used is often difficult. The ransom note might contain a personal ID. If the personal ID ends with t1, it might indicate an offline key, but this is not a definitive guarantee.
  • Broader Impact:
    • Widespread Individual Impact: Due to its common attack vectors (cracked software, fake updates), STOP/Djvu primarily targets individual users and small businesses, leading to significant personal data loss and financial distress.
    • Fueling Cybercrime Ecosystem: The high volume of successful infections generates substantial revenue for the attackers, allowing them to fund further development and expand their operations, contributing to the overall growth of the cybercrime ecosystem.
    • Reputational Damage: For small businesses, an infection can lead to a loss of customer trust and significant downtime, impacting operations and revenue.