*udjvu

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The ransomware variant identified by the file extension *udjvu is a member of the notorious STOP/Djvu ransomware family. This family has undergone numerous iterations, each typically marked by a unique file extension. It primarily targets individual users and small businesses through deceptive distribution methods.

This document provides a comprehensive breakdown of *udjvu, covering its technical characteristics and offering practical recovery strategies.

Technical Breakdown:

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: When files are encrypted by this specific variant, they will have the .udjvu extension appended to their original filename.

  • Renaming Convention: The ransomware encrypts a wide range of file types (documents, images, videos, archives, databases, etc.). The renaming pattern is straightforward:
    original_filename.original_extension.udjvu
    For example:

    • document.docx becomes document.docx.udjvu
    • photo.jpg becomes photo.jpg.udjvu
    • video.mp4 becomes video.mp4.udjvu

    Additionally, 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 first emerged in late 2017/early 2018. The .udjvu variant, like many others with different extensions (e.g., .zzza, .jjjp, .lool), appeared as part of the family’s continuous evolution. While a precise “start date” for .udjvu specifically is hard to pinpoint, it was observed to be prevalent in late 2019 and early 2020, fitting into the ongoing lifecycle of this highly active ransomware. New extensions are released regularly, maintaining its threat level.

3. Primary Attack Vectors

The STOP/Djvu ransomware family, including the .udjvu variant, relies heavily on social engineering and deceptive tactics rather than sophisticated network exploitation. Its primary propagation mechanisms include:

  • Software Cracks and Pirated Software: This is the most common and effective vector. Users download “free” or “cracked” versions of popular paid software (e.g., Adobe Photoshop, Microsoft Office, games, VPNs, video editing suites) from untrustworthy websites, torrent sites, or file-sharing platforms. The ransomware executable is bundled within these seemingly legitimate installers.
  • Bundled Downloads: It can be distributed as part of “free” software bundles, freeware, shareware, or fake software updates obtained from dubious download portals. The user is tricked into installing the ransomware alongside desired software.
  • Malvertising: While less frequent than pirated software, malicious advertisements can redirect users to compromised websites or initiate drive-by downloads that contain the ransomware.
  • Fake Online Installers/Updaters: Some instances have been observed where users are prompted to download fake updates for Flash Player, Java, or other common software, which covertly install the ransomware.
  • Phishing/Spam Campaigns (Less Common): While generally not the primary method for Djvu/STOP, like any malware, it can potentially be delivered via malicious email attachments (e.g., seemingly legitimate invoices, shipping notifications) or links that lead to compromised download sites. However, its main distinction is that it doesn’t typically exploit network vulnerabilities (like EternalBlue or RDP flaws) for widespread enterprise compromise.

Remediation & Recovery Strategies:

1. Prevention

Proactive measures are crucial to defend against *udjvu and similar ransomware threats:

  • User Education: The most effective defense against Djvu/STOP ransomware is educating users about the dangers of pirated software, suspicious downloads, and untrusted websites.
  • Reputable Software Sources: Always download software directly from official vendor websites, trusted app stores (e.g., Microsoft Store, Google Play), or highly reputable distributors. Avoid torrent sites, “free software” aggregators, or unofficial download portals.
  • Robust Antivirus/Endpoint Detection and Response (EDR): Install and maintain an up-to-date antivirus or EDR solution with real-time protection enabled. Ensure it’s configured to perform regular full system scans.
  • Regular Backups (3-2-1 Rule): Implement a comprehensive backup strategy. Follow the “3-2-1 rule”:
    • 3 copies of your data.
    • On 2 different media types.
    • 1 copy offsite or in the cloud (disconnected from your network after backup is complete).
    • Regularly test your backups to ensure data integrity and restorability.
  • System and Software Updates: Keep your operating system (Windows, macOS), web browsers, and all installed applications patched with the latest security updates. This closes vulnerabilities that could potentially be exploited.
  • Firewall Configuration: Maintain a properly configured firewall (both hardware and software) to block suspicious inbound and outbound connections.
  • Ad Blockers/Script Blockers: Use browser extensions that block malicious ads and scripts, which can help prevent redirection to compromised sites or the download of malware.
  • Disable/Limit Admin Privileges: Operate with standard user accounts as much as possible. Only use administrator accounts when absolutely necessary for system changes.

2. Removal

If your system is infected, follow these steps to remove the *udjvu ransomware:

  • 1. Isolate the Infected System: Immediately disconnect the infected computer from the internet (unplug Ethernet cable, disable Wi-Fi). This prevents further encryption of network shares and stops potential communication with the attacker’s command-and-control (C2) server.
  • 2. Identify Ransom Note: Locate the _readme.txt file (usually on the desktop or in encrypted folders). This note contains the attacker’s demands and contact information. Do not contact the attackers or pay the ransom.
  • 3. Boot into Safe Mode (Recommended): Restart your computer and boot into Safe Mode with Networking. This loads only essential services and drivers, making it easier for security software to operate without interference from the ransomware.
  • 4. Scan with Reputable Anti-Malware:
    • Download and run a full system scan using a trusted, up-to-date anti-malware solution. Examples include Malwarebytes, SpyHunter, ESET, Kaspersky, or Sophos.
    • Allow the software to quarantine or remove all detected malicious files and registry entries associated with *udjvu.
  • 5. Check for Host File Modifications: *udjvu variants often modify the C:\Windows\System32\drivers\etc\hosts file to block access to cybersecurity websites. Open this file with Notepad (as administrator) and delete any suspicious entries that point legitimate security sites to 127.0.0.1 or other local IP addresses. Save the changes.
  • 6. Clean Up Temporary Files and Startup Items:
    • Use Disk Cleanup or manually delete content from C:\Temp and %TEMP%.
    • Check Task Scheduler (taskschd.msc) for suspicious tasks set to run at startup or regularly.
    • Check startup programs in Task Manager (Windows 10/11) or msconfig (older Windows) and disable any unknown entries.
  • 7. Perform a Full System Scan Again: After initial cleanup, run another full scan to ensure all remnants are removed.
  • 8. Change All Passwords: Since Djvu/STOP variants often drop info-stealers, assume all credentials on the infected system (browser passwords, stored login details, email, online banking, etc.) have been compromised. Change all critical passwords from a different, clean device.

3. File Decryption & Recovery

  • Recovery Feasibility:
    • Online Keys: Most *udjvu infections use “online keys.” This means a unique encryption key is generated for each victim upon connecting to the attacker’s C2 server. If an online key was used, decryption without paying the ransom is extremely difficult, if not impossible, unless security researchers manage to obtain or crack the specific key (which is rare).
    • Offline Keys: In rare cases, if the ransomware fails to connect to its C2 server during encryption, it might resort to using a limited set of “offline keys.” If your files were encrypted with an offline key, there is a possibility of decryption.
    • Shadow Volume Copies (VSS): *udjvu variants typically use vssadmin.exe Delete Shadows /All /Quiet to delete all shadow volume copies, making recovery via Windows’ built-in restore points highly unlikely.
  • Essential Tools/Patches:
    • Emsisoft Decryptor for STOP Djvu Ransomware: This is the primary tool available for attempting decryption. Emsisoft, in collaboration with the No More Ransom project, regularly updates its decryptor.
      • How it works: The decryptor attempts to identify if your files were encrypted with an online or offline key. For offline keys, it can often decrypt files. For online keys, it can only decrypt if your specific ID’s key has been recovered and added to their database.
      • Requirements: You’ll typically need at least one pair of encrypted and its corresponding original (unencrypted) file to help the decryptor identify the correct key. This is often challenging to provide for most users.
    • Data Recovery Software: Tools like PhotoRec, Recuva, or Disk Drill can sometimes recover fragments of original files, particularly if the files were large and not completely overwritten. However, this is not a reliable method for full recovery of all encrypted data and should be considered a last resort.
    • Backups: Restoring from clean, offsite backups is the most reliable and recommended method for file recovery. Ensure your backups were created before the infection and are isolated from the network to prevent them from being encrypted.

4. Other Critical Information

  • Additional Precautions:
    • Info-Stealer Payload: A significant characteristic of many Djvu/STOP variants, including *udjvu, is that they often deliver an information-stealing malware (e.g., Azorult, Vidar, RedLine Stealer) before the file encryption process begins. This means that even if you manage to decrypt or recover your files, your sensitive data (browser history, stored credentials, cryptocurrency wallets, system information) may have already been exfiltrated by the attackers. This necessitates a complete password change on all online accounts accessible from the infected machine.
    • Hosts File Modification: As mentioned under removal, the ransomware frequently modifies the Windows hosts file to redirect domains of security-related websites (antivirus vendors, security blogs) to 127.0.0.1 (localhost), preventing the victim from accessing help or downloading security tools.
  • Broader Impact:
    • Global Reach and Persistence: The Djvu/STOP ransomware family has a significant global impact due to its effective distribution via pirated software, reaching millions of individual users and small businesses worldwide. Its constant evolution with new extensions ensures its persistence as a major threat.
    • Financial and Emotional Toll: The combination of data loss, potential identity theft (due to info-stealers), and the emotional distress of losing irreplaceable files (like family photos) places a heavy burden on victims.
    • Lesson in Software Piracy: The prevalence of this ransomware serves as a stark reminder of the inherent risks associated with downloading pirated software. The “free” software often comes at the much higher cost of data compromise and system infection.