!!restore-my-file-kavva.txt

[Content by Gemini 2.5]

This document provides a comprehensive analysis of the ransomware variant identified by the presence of the !!restore-my-file-kavva.txt ransom note, which is strongly associated with the STOP/Djvu ransomware family. While !!restore-my-file-kavva.txt is the name of the ransom note, the actual encrypted files will have a specific extension, often .[random_characters] or .kavva itself.

Technical Breakdown:

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: The string !!restore-my-file-kavva.txt is not the file extension appended to encrypted files, but rather the name of the ransom note dropped by the ransomware. This note contains instructions for the victim on how to pay the ransom to decrypt their files.
  • Renaming Convention: Files encrypted by this variant (and other STOP/Djvu variants) will typically have a new, unique extension appended to their original filenames. For example, a file named document.docx might be renamed to document.docx.kavva, document.docx.lqqw, document.docx.rloo, or similar. The specific extension changes frequently with new variants released by the threat actors. In addition to file encryption, the ransomware also encrypts specific user data files such as documents, photos, videos, archives, and databases.

2. Detection & Outbreak Timeline

  • Approximate Start Date/Period: The STOP/Djvu ransomware family, to which the “Kavva” variant belongs, has been highly active since late 2018/early 2019 and continues to be one of the most prevalent consumer-targeting ransomware threats. Specific variants like those dropping notes like !!restore-my-file-kavva.txt emerge as part of this ongoing activity, with new extensions and slight modifications being released consistently, sometimes daily or weekly. The “Kavva” specific variant would have appeared within this broader timeline, likely in 2023 or 2024, as a newer iteration.

3. Primary Attack Vectors

The Kavva ransomware variant, like its STOP/Djvu predecessors, primarily relies on social engineering and deceptive tactics:

  • Cracked Software/Pirated Content: This is the most common infection vector. Users download compromised installers for pirated software (e.g., Adobe Photoshop, Microsoft Office, various games, video editing tools, VPNs, keygens, software cracks) from unreliable websites, torrents, or file-sharing platforms. The ransomware is bundled silently within these seemingly legitimate installers.
  • Malicious Websites/Pop-ups: Visiting compromised or malicious websites that push deceptive ads, fake update prompts (e.g., “Flash Player update required”), or offer “free” software downloads can lead to infection.
  • Email Phishing Campaigns: Less common for STOP/Djvu, but still a possibility. Malicious attachments (e.g., seemingly legitimate invoices, shipping notifications, or resumes) or links within phishing emails that download the malware directly.
  • Drive-by Downloads: Exploitation of browser or software vulnerabilities to download and execute the ransomware without explicit user interaction, though this is less frequent for this family compared to tricking the user into running an installer.
  • Fake System Optimizers/Antivirus: Disguising itself as legitimate system tools or security software.

Remediation & Recovery Strategies:

1. Prevention

Proactive measures are crucial to avoid infection:

  • Regular Backups: Implement a robust backup strategy. Store critical data on external drives or cloud services that are disconnected or isolated from the main network when not actively backing up. This is the most effective defense against ransomware.
  • Software & OS Updates: Keep your operating system (Windows, macOS) and all software (browsers, antivirus, applications) fully updated with the latest security patches. This closes vulnerabilities that attackers might exploit.
  • Reputable Antivirus/Anti-Malware: Install and maintain a reputable antivirus/anti-malware solution with real-time protection. Ensure its definitions are consistently updated.
  • Software Whitelisting: For organizations, consider implementing application whitelisting to prevent unauthorized executables from running.
  • Email Security: Be extremely cautious with email attachments and links, especially from unknown senders. Verify sender identity for suspicious emails.
  • Ad Blockers: Use browser ad-blockers to prevent accidental clicks on malicious advertisements.
  • Avoid Pirated Software: Never download or use cracked software, keygens, or activators. These are primary vectors for ransomware like Kavva.
  • Strong Passwords & MFA: Use strong, unique passwords for all accounts and enable multi-factor authentication (MFA) wherever possible to protect against account compromise that could lead to broader network infection.
  • Disable RDP (if not needed): If Remote Desktop Protocol is not essential, disable it. If required, secure it with strong passwords, network level authentication (NLA), and restrict access to trusted IPs only.

2. Removal

The goal of removal is to stop the ransomware’s processes and prevent further damage or reinfection.

  1. Isolate the Infected System: Immediately disconnect the infected computer from the internet and any local networks (Wi-Fi, Ethernet). This prevents the ransomware from spreading to other devices and contacting its command-and-control server.
  2. Identify and Stop Malicious Processes:
    • Reboot the computer into Safe Mode with Networking. This loads only essential services, often preventing the ransomware from fully executing.
    • Open Task Manager (Ctrl+Shift+Esc) and look for suspicious processes with unfamiliar names or high resource usage. End these processes.
  3. Scan with Antivirus/Anti-Malware:
    • Run a full system scan using your updated reputable antivirus software (e.g., Malwarebytes, Windows Defender, Emsisoft Anti-Malware). These tools are often effective at identifying and quarantining the ransomware executable.
    • Consider using a second-opinion scanner for thoroughness.
  4. Delete Malicious Files: Remove any identified malicious executables, associated files, and registry entries. Your antivirus should handle this, but manual verification might be necessary if you’re an advanced user.
  5. Clean up Scheduled Tasks: Ransomware often creates scheduled tasks to ensure persistence. Check Task Scheduler and remove any suspicious entries.
  6. Restore System to a Clean State (if necessary): If you have a system restore point created before the infection, you can attempt to revert to it. However, this will not decrypt files and might not fully remove the malware components, so a full scan afterwards is still essential. A clean OS reinstall is often the most secure option for heavily compromised systems.

3. File Decryption & Recovery

  • Recovery Feasibility: Decrypting files encrypted by the Kavva/STOP/Djvu ransomware family without paying the ransom is challenging but sometimes possible. The feasibility largely depends on whether your system was online or offline during the encryption process:
    • Online ID Encryption (Most Common): If your computer was connected to the internet during the attack, the ransomware communicates with its C2 server and obtains a unique “online key” for your system. Files encrypted with an online key are generally not decryptable without the specific private key held by the attackers, or if a master key is ever leaked by law enforcement or researchers (which is rare).
    • Offline ID Encryption (Less Common): If your computer was completely offline during the attack, the ransomware resorts to using a pre-generated “offline key.” While still difficult, files encrypted with offline keys can sometimes be decrypted if the specific offline key variant is known and integrated into a public decryption tool.
  • Methods or Tools Available:
    • Emsisoft Decryptor for STOP/Djvu: Emsisoft, in collaboration with the No More Ransom! project, offers a free decryptor tool for the STOP/Djvu ransomware. This tool requires the victim to provide one encrypted file and its original, unencrypted version (if available) to help identify the specific variant and key. It is particularly effective for files encrypted with offline IDs. For online IDs, it will likely state that decryption is not possible.
    • No More Ransom! Project: Always check the No More Ransom! website (nomoreransom.org). They are a collaborative initiative that collects and provides free decryption tools for various ransomware families, including many STOP/Djvu variants.
    • Data Recovery Software (for Shadow Copies): The ransomware typically deletes Volume Shadow Copies (VSCs) to prevent easy recovery. However, sometimes it fails, or fragments of files might remain. Tools like PhotoRec, Recuva, or Disk Drill might be able to recover older, unencrypted versions of some files if they weren’t completely overwritten or if VSCs were not fully deleted. This is a long shot and not a guaranteed solution for all files.
    • Professional Data Recovery: For critical data where all else fails and you refuse to pay, specialized data recovery firms might offer services. However, success is not guaranteed, and costs are very high.
  • Paying the Ransom: Cybersecurity experts generally advise against paying the ransom. There is no guarantee that the attackers will provide a working decryptor, and paying perpetuates the ransomware business model. However, for organizations with critical data and no viable backups, it sometimes becomes a last resort. If you consider this option, engage with law enforcement and legal counsel.

4. Other Critical Information

  • Unique Characteristics:
    • Frequent Variant Updates: The STOP/Djvu family is notorious for its rapid evolution, with new encryption extensions and slightly modified code appearing almost daily, making it a moving target for decryptor development.
    • Information Stealer Component: Many STOP/Djvu variants are bundled with other malware, most commonly RedLine Stealer or similar info-stealing malware. This means that in addition to encrypting files, your sensitive information (passwords, cryptocurrency wallets, browser data, banking details) might have been exfiltrated from your system.
    • Offline vs. Online IDs: This is a crucial distinction for victims. The PersonalID.txt file (or similar) found alongside the ransom note will contain a victim ID. If this ID ends in t1, it’s an offline ID, offering a glimmer of hope for decryption. If it doesn’t end in t1, it’s an online ID, and decryption without the attacker’s key is highly improbable.
    • Ransom Note Consistency: The ransom note format (!!restore-my-file-kavva.txt or _readme.txt) and content (demanding payment via cryptocurrency, specific contact emails) are fairly consistent across STOP/Djvu variants.
  • Broader Impact:
    • Widespread Individual Victimization: Unlike some targeted enterprise ransomware, STOP/Djvu focuses on mass infection of individual users, making it one of the most common forms of ransomware encountered by the general public.
    • Financial Loss: Victims face the potential loss of irrecoverable data and the financial cost of ransom payments (typically hundreds to over a thousand USD in cryptocurrency), or the cost of professional data recovery services.
    • Identity Theft/Further Compromise: The inclusion of information stealers means victims are at risk of secondary attacks, including account takeovers, financial fraud, and identity theft, even if they manage to recover their encrypted files.
    • System Reinstallation: Due to the difficulty of complete removal and the potential for bundled malware, many security professionals recommend a clean reinstallation of the operating system after a STOP/Djvu infection to ensure the system is truly free of malicious components.

By understanding these technical details and implementing the recommended strategies, individuals and organizations can better protect themselves against the Kavva ransomware variant and mitigate its potential damage.