492

[Content by Gemini 2.5]

The ransomware variant identified by the file extension .492 is a variant of the STOP/Djvu ransomware family. This family is one of the most prolific consumer-grade ransomware types, constantly releasing new versions with slight modifications, primarily to their appended file extensions.

Here’s a detailed breakdown of the .492 variant and strategies to combat it:

Technical Breakdown:

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: The exact file extension used by this variant is .492.
  • Renaming Convention: When a file is encrypted by the .492 variant, it appends .492 to the original file name, typically after its original extension.
    • Example:
      • document.docx becomes document.docx.492
      • image.jpg becomes image.jpg.492
      • archive.zip becomes archive.zip.492
        In addition to file encryption, the ransomware drops a ransom note named _readme.txt in every folder containing encrypted files.

2. Detection & Outbreak Timeline

  • Approximate Start Date/Period: The STOP/Djvu ransomware family, in general, has been active since late 2017/early 2018. New variants, like .492, are released frequently, sometimes daily or weekly, often incorporating minor changes (like the new file extension). The .492 variant would have appeared as part of this ongoing release cycle, typically in late 2023 or early 2024, continuing the family’s persistent activity.

3. Primary Attack Vectors

The STOP/Djvu family, including the .492 variant, primarily relies on social engineering and deceptive tactics for propagation:

  • Cracked Software/Software Activators: This is the most common vector. Users download and execute “cracked” versions of popular software (e.g., Photoshop, Microsoft Office, games) or “keygen” and “patch” tools from torrent sites or shady download portals. These executables often contain the ransomware payload.
  • Fake Software Updates: Malicious websites may present fake software updates (e.g., for Flash Player, Java, web browsers) that, when downloaded and run, install the ransomware.
  • Malicious Downloads & Drive-by Downloads: Visiting compromised websites or clicking on malicious ads can sometimes trigger automatic downloads of the ransomware, though less common than cracked software.
  • Phishing/Spam Campaigns (Less Common for Djvu): While common for other ransomware, email-based phishing campaigns are less of a primary vector for Djvu compared to its reliance on pirated software. However, emails containing malicious attachments or links disguised as invoices, shipping notifications, or other legitimate communications can still be used.
  • Trojanized Installers: The ransomware can be bundled with legitimate software installers downloaded from untrustworthy sources.

Remediation & Recovery Strategies:

1. Prevention

Proactive measures are crucial to avoid infection:

  • 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 routinely tested and stored disconnected from the main network to prevent them from being encrypted.
  • Software Updates: Keep your operating system (Windows, macOS, Linux) and all software applications (browsers, anti-virus, productivity suites, etc.) fully patched and up-to-date. This closes security vulnerabilities that ransomware might exploit.
  • Reputable Antivirus/Anti-Malware: Use a strong, reputable antivirus or Endpoint Detection and Response (EDR) solution and keep its definitions updated. Enable real-time protection.
  • User Education: Educate users about the dangers of downloading pirated software, clicking suspicious links, or opening attachments from unknown senders. Emphasize the risks associated with cracked software.
  • Firewall Configuration: Configure your firewall to block outbound connections to known malicious IP addresses and restrict unnecessary incoming connections.
  • Disable RDP if Unnecessary: If Remote Desktop Protocol (RDP) is not required, disable it. If it is needed, secure it with strong, unique passwords, multi-factor authentication (MFA), and network-level authentication (NLA), and restrict access to trusted IPs.
  • Ad-Blockers: Use browser ad-blockers to prevent drive-by downloads from malicious advertisements.

2. Removal

  • Immediate Disconnection: As soon as an infection is suspected (e.g., appearance of .492 files, _readme.txt notes, system slowdown), immediately disconnect the infected system from the network (unplug Ethernet cable, disable Wi-Fi). This prevents further spread to connected devices and stops communication with the C2 server.
  • Identify & Isolate: Determine which systems are infected. Isolate them from the rest of the network.
  • Boot into Safe Mode: Reboot the infected computer into Safe Mode with Networking. This often prevents the ransomware from fully executing its payload and allows for easier removal.
  • Full System Scan: Perform a comprehensive scan using a reputable anti-malware tool (e.g., Malwarebytes, SpyHunter, your updated antivirus). Allow the tool to quarantine or remove all detected threats.
  • Remove Ransom Note: Delete all _readme.txt files found on the system.
  • Check for Persistent Mechanisms: The ransomware might create persistence mechanisms (e.g., modifying registry keys, creating scheduled tasks). Advanced users can check these areas manually or use specialized tools like Autoruns (Sysinternals) to identify and disable them.
  • Change Passwords: After confirming the system is clean, change all passwords, especially for online accounts, as the ransomware might attempt to exfiltrate credentials.

3. File Decryption & Recovery

  • Recovery Feasibility:
    • Emsisoft Decryptor for STOP/Djvu: The most promising method for .492 is to use the Emsisoft Decryptor for STOP Djvu Ransomware. This tool is continuously updated by Emsisoft in collaboration with victims and security researchers.
    • Online vs. Offline Keys: STOP/Djvu variants like .492 encrypt files using either an “online key” or an “offline key.”
      • Online Key: If the ransomware was able to communicate with its command-and-control (C2) server during encryption, it uses a unique “online key” for that specific infection. These keys are generally impossible to decrypt without the attacker’s master key or paying the ransom.
      • Offline Key: If the ransomware failed to connect to its C2 server (e.g., due to no internet connection), it uses a pre-generated “offline key.” These offline keys are often shared across many infections. If Emsisoft’s tool has identified and added the specific offline key used by .492 to its database, decryption is possible. The decryptor will often tell you if an online or offline key was used.
    • Data Recovery Software: In some cases, third-party data recovery software (e.g., PhotoRec, Recuva) might be able to recover older, unencrypted versions of files or shadow copies, but success rates vary wildly and depend on how much the ransomware overwrites data.
  • Essential Tools/Patches:
    • Emsisoft Decryptor for STOP Djvu Ransomware: Download this tool only from Emsisoft’s official website.
    • Reputable Anti-Malware Software: Malwarebytes, SpyHunter, Avast, AVG, Windows Defender (ensure it’s updated).
    • System Restore/Shadow Copies: While often deleted by ransomware, check if System Restore Points or Volume Shadow Copies exist. This can be done via file properties (Previous Versions tab) or command line (vssadmin list shadows).
    • Backups: The most reliable “tool” for recovery remains up-to-date, offline backups.

4. Other Critical Information

  • Additional Precautions:
    • Disables Windows Defender: Many STOP/Djvu variants, including .492, attempt to disable Windows Defender and other security software to hinder detection and removal. Verify your security software is active after removal.
    • Host File Modification: The ransomware may modify the hosts file to block access to security-related websites (e.g., antivirus vendors’ sites, security news sites) to prevent victims from seeking help or downloading tools. Check and reset the hosts file if necessary. (Located at C:\Windows\System32\drivers\etc\hosts).
    • Information Stealer Component: Recent STOP/Djvu variants often include an information-stealing module (e.g., Vidar, Azorult, RedLine Stealer) that attempts to steal passwords, cryptocurrency wallet information, browser cookies, and other sensitive data before encrypting files. Assume your credentials have been compromised and change all critical passwords immediately after cleaning the system.
  • Broader Impact:
    • High Volume, Broad Target: STOP/Djvu is one of the most widespread ransomware families, primarily targeting individual users and small to medium-sized businesses rather than large enterprises. Its sheer volume of infections makes it a significant threat.
    • Psychological Impact: The frequent emergence of new variants and the difficulty of decryption for “online key” infections contribute to significant distress and financial loss for victims.
    • Reinforces Best Practices: The prevalence of Djvu variants strongly underscores the importance of basic cybersecurity hygiene: robust backups, skepticism towards unofficial software, and prompt software updates.