3rnu

[Content by Gemini 2.5]

As a cybersecurity expert specializing in ransomware, I’ve compiled a detailed resource regarding the ransomware variant identified by the file extension .3rnu. It’s important to note that while .3rnu specifically refers to the file extension, it often indicates a variant of a broader, more established ransomware family, commonly STOP/Djvu ransomware, which frequently uses unique, seemingly random 3-4 character extensions for each new variant. Precise public information solely on a “3rnu ransomware family” is scarce, reinforcing the likelihood that this is a specific variant’s marker rather than a distinct, new ransomware family.

Technical Breakdown:

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: Files encrypted by this ransomware will have the .3rnu extension appended to their original filenames.
  • Renaming Convention: The typical renaming pattern involves adding the .3rnu extension directly after the original file extension. For example, a file named document.docx would be renamed to document.docx.3rnu. In some cases, ransomware variants may also append a unique victim ID before the extension (e.g., document.docx.[ID-XXXXXX].3rnu), or drop a ransom note with a variant-specific name (e.g., _readme.txt is common for STOP/Djvu variants).

2. Detection & Outbreak Timeline

  • Approximate Start Date/Period: Specific public intelligence for a “3rnu ransomware” as a distinct family is limited. However, file extensions like .3rnu are characteristic of new variants from active ransomware families, most notably the STOP/Djvu ransomware family. New variants of STOP/Djvu emerge frequently, sometimes on a daily or weekly basis. Therefore, the .3rnu variant would have likely appeared within the ongoing operations of this larger family, possibly in late 2023 or early 2024, given its recent identification. Its spread would align with the existing infrastructure and campaigns of the parent ransomware group.

3. Primary Attack Vectors

The propagation mechanisms for variants using extensions like .3rnu (especially if linked to STOP/Djvu) are typical for widespread consumer-facing ransomware:

  • Software Cracks/Keygens & Pirated Software: This is one of the most prevalent methods. Users download pirated software, cracked versions of legitimate programs, or key generators from torrent sites or untrusted download portals. The ransomware is bundled with these downloads, often disguised as part of the installation process.
  • Malicious Email Campaigns (Phishing/Spear-Phishing): Attackers send emails containing malicious attachments (e.g., seemingly legitimate documents with embedded macros, or archives containing executables) or links to compromised websites.
  • Malvertising & Drive-by Downloads: Users visiting compromised or malicious websites may be subjected to drive-by downloads where the ransomware is automatically downloaded to their system without their explicit interaction, often by exploiting browser or plugin vulnerabilities. Malvertising campaigns direct users to such sites.
  • Fake Software Updates: Pop-ups or alerts promoting fake updates for common software (e.g., Flash Player, Java, web browsers) can lead to the download and execution of the ransomware.
  • Exploitation of Vulnerabilities (Less Common for Consumer-Grade Ransomware): While less common for variants like .3rnu, some ransomware leverages unpatched software vulnerabilities (e.g., in operating systems, network services like SMBv1, or web applications) to gain initial access.
  • Remote Desktop Protocol (RDP) Exploits: Weak or compromised RDP credentials allow attackers to gain direct access to a system and manually deploy the ransomware. This is more common in targeted attacks on businesses.

Remediation & Recovery Strategies:

1. Prevention

Proactive measures are the most effective defense against .3rnu and similar ransomware variants:

  • Regular Data Backups: Implement a robust backup strategy following the 3-2-1 rule (3 copies of data, on 2 different media, with 1 offsite/offline). Ensure backups are immutable or regularly disconnected from the network to prevent encryption.
  • Robust Endpoint Protection: Deploy reputable antivirus and anti-malware software with real-time protection, behavioral analysis, and exploit prevention capabilities. Keep these solutions updated.
  • Software & OS Patching: Regularly update your operating system, applications, and firmware to patch known vulnerabilities that attackers could exploit. Enable automatic updates where possible.
  • Email Security: Use strong spam filters, exercise extreme caution with email attachments and links, and verify the sender’s authenticity. Avoid opening emails from unknown sources.
  • Network Segmentation: For organizational networks, segmenting networks can limit the lateral movement of ransomware if an infection occurs.
  • Strong Passwords & Multi-Factor Authentication (MFA): Implement strong, unique passwords for all accounts and enable MFA wherever possible, especially for remote access services (RDP, VPN) and critical accounts.
  • User Education: Train users to recognize phishing attempts, avoid downloading pirated software, and be wary of suspicious links and attachments.
  • Disable Unnecessary Services: Disable services like RDP if not needed, or secure them with strong passwords, MFA, and network-level restrictions.
  • Application Whitelisting: Implement application whitelisting to prevent unauthorized executables from running on your systems.

2. Removal

If a system is infected with .3rnu, follow these steps for effective removal:

  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 on the network.
  2. Identify the Ransomware: Look for the .3rnu extension on encrypted files and the ransom note (often _readme.txt or similar). This confirms the specific variant.
  3. Boot into Safe Mode: Restart the computer in Safe Mode (with Networking, if necessary, to download tools) to prevent the ransomware from running its malicious processes.
  4. Perform Full System Scans: Use reputable antivirus/anti-malware software (e.g., Malwarebytes, HitmanPro, Emsisoft Anti-Malware, your current AV solution) to perform a full, deep scan. Ensure the definitions are up-to-date. These tools can identify and remove the ransomware executable and associated components.
  5. Remove Identified Threats: Allow the security software to quarantine or remove all detected malicious files.
  6. Check for Persistence Mechanisms: Manually (if experienced) or using specialized tools, check common ransomware persistence locations such as:
    • Startup folders (Registry Run keys, Startup folder entries)
    • Scheduled Tasks
    • Services
    • Browser extensions
    • Temp folders
  7. Patch Vulnerabilities: Ensure the operating system and all software are fully patched to prevent re-infection.
  8. Change Credentials: Change all passwords for accounts accessed from the infected system, especially network shares, cloud services, and email.

3. File Decryption & Recovery

  • Recovery Feasibility:
    • Without Payment: Decrypting files encrypted by .3rnu (and most STOP/Djvu variants) without the attacker’s private key is challenging but sometimes possible.
      • Offline Keys: If your system was encrypted without an active internet connection (using an “offline key”), there’s a higher chance of decryption. Security researchers often manage to recover these keys over time and integrate them into decryption tools.
      • Online Keys: If your system was connected to the internet during encryption, the ransomware likely used a unique “online key” for your system, making decryption without the attacker’s specific key virtually impossible.
    • Decryption Tools:
      • Emsisoft Decryptor for STOP/Djvu: This is the primary tool to attempt decryption for .3rnu if it is indeed a STOP/Djvu variant. Emsisoft, in collaboration with the No More Ransom project, regularly updates their decryptor with newly discovered keys. You will need at least one pair of an original (unencrypted) file and its encrypted version to help the tool identify the correct key.
      • No More Ransom Project: Always check the No More Ransom website (nomoreransom.org) for free decryption tools. They consolidate decrypters from various cybersecurity vendors.
    • Payment: Paying the ransom is strongly discouraged. There is no guarantee you will receive the decryption key, and it funds future criminal activities.
  • Essential Tools/Patches:
    • Emsisoft Decryptor for STOP/Djvu Ransomware: Download this tool from Emsisoft or No More Ransom.
    • Reputable Anti-malware Software: Malwarebytes, ESET, Sophos, Avast, etc., for initial cleanup.
    • Operating System Patches: Ensure Windows Update (or macOS/Linux equivalent) is fully applied.
    • Software Updates: Browser, Adobe products, Java, Microsoft Office, etc.
    • Data Recovery Software: In some rare cases, data recovery software might retrieve shadow copies or deleted unencrypted versions of files, but ransomware often attempts to delete these.
    • Backup Solutions: Crucial for restoring files after removal.

4. Other Critical Information

  • Additional Precautions:
    • Shadow Copies Deletion: Like many modern ransomware variants, .3rnu (especially if STOP/Djvu) attempts to delete Volume Shadow Copies (vssadmin delete shadows /all /quiet) to prevent easy restoration of files.
    • Hosts File Modification: Some variants may modify the hosts file to block access to security websites or update servers.
    • Double Extortion (Less Common for this type): While not typically associated with consumer-facing ransomware like STOP/Djvu, some ransomware families engage in double extortion (encrypting data AND exfiltrating it) to pressure victims. Always assume data compromise if an infection occurs.
    • Information Stealers: STOP/Djvu variants are often bundled with information stealer malware (e.g., Vidar, RedLine Stealer, AZORult). Even if you decrypt your files, assume your sensitive credentials (passwords, browser data, cryptocurrency wallets) might have been compromised. Change all critical passwords immediately and monitor financial accounts.
  • Broader Impact:
    • Significant Financial Loss: For individuals, the loss of irrecoverable personal data can be devastating. For organizations, the cost of downtime, recovery efforts, and potential ransom payments can be substantial.
    • Operational Disruption: Business operations can grind to a halt, leading to lost productivity and revenue.
    • Data Loss: If backups are not available or are also compromised, permanent data loss is a high risk.
    • Reputational Damage: For businesses, an attack can erode customer trust and damage public image.
    • Emotional Distress: For individuals, the loss of irreplaceable photos, documents, and other personal files can cause significant emotional distress.

Always prioritize prevention through robust security practices and maintain comprehensive, offline backups. If infected, avoid panicking and consult reputable cybersecurity resources and professionals.