@inbox.ru*

[Content by Gemini 2.5]

The ransomware variant identified by the file extension or contact email ending with @inbox.ru* is a hallmark characteristic of the STOP/Djvu ransomware family. This family is one of the most prolific and continuously evolving threats, primarily targeting individual users and small businesses through highly accessible vectors.

Technical Breakdown:

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: While the prompt mentions @inbox.ru* (which is typically part of the contact email in the ransom note), the actual encrypted file extension for STOP/Djvu variants using @inbox.ru for contact usually follows a specific pattern. It’s often a four-character string (e.g., .qall, .repp, .rstr, .coot, etc.) appended to the original file name. The specific extension changes frequently with new variants.
    • Example: A file named document.docx might become document.docx.qall or document.docx.rstr.
  • Renaming Convention: The ransomware typically encrypts files without changing the base filename, but appends its unique extension to the original file’s extension. For instance, photo.jpg becomes photo.jpg.[4-character-extension]. There is no addition of an ID or the email directly into the filename itself, unlike some other ransomware families.

2. Detection & Outbreak Timeline

  • Approximate Start Date/Period: The STOP/Djvu ransomware family first emerged around late 2017/early 2018 (as Djvu, then evolving into STOP). Variants featuring @inbox.ru (and other email providers like @gmx.de, @mail.fr, @aol.com) for contact information have been consistently active and widespread since mid-2018 and continue to be one of the most prevalent consumer-facing ransomware threats. Its high volume of new variants ensures a continuous stream of outbreaks.

3. Primary Attack Vectors

  • Propagation Mechanisms: STOP/Djvu ransomware variants, including those using @inbox.ru contacts, predominantly rely on social engineering and deceptive tactics rather than complex exploit chains for initial access.
    • Cracked Software/Pirated Content: This is the most common vector. Users download “free” or “cracked” versions of popular software (e.g., Adobe Photoshop, Microsoft Office, video games, VPNs, Windows activators, video converters) from torrent sites, warez forums, or untrusted download portals. The ransomware is bundled within these seemingly legitimate installers or executables.
    • Fake Software Updates: Pop-up ads or websites disguised as legitimate software update prompts (e.g., Flash Player, Java, browser updates) trick users into downloading and executing the malicious payload.
    • Malvertising/Compromised Websites: Malicious advertisements or scripts embedded on compromised websites can lead to automatic downloads or deceptive prompts for “essential” software, which are actually the ransomware executables.
    • Phishing Campaigns: While less common than cracked software for STOP/Djvu, basic phishing emails containing malicious attachments (e.g., seemingly legitimate invoices, order confirmations, or shipping notices) can also be used.
    • Remote Desktop Protocol (RDP) Exploits: While not a primary vector for mass distribution of Djvu, poorly secured RDP endpoints can be brute-forced or exploited, allowing attackers to manually deploy the ransomware. This is more common for targeted attacks on businesses.
    • Software Vulnerabilities: Generally, STOP/Djvu does not rely on sophisticated zero-day exploits (like EternalBlue for WannaCry) for its widespread distribution. Its success lies in exploiting human psychology and a lack of user vigilance.

Remediation & Recovery Strategies:

1. Prevention

  • Proactive Measures:
    1. Regular Backups: Implement a robust 3-2-1 backup strategy (3 copies, 2 different media types, 1 offsite/cloud). Ensure backups are isolated from the network to prevent encryption.
    2. Use Legitimate Software: Only download software from official vendor websites or trusted app stores. Avoid cracked software, key generators, or activators.
    3. Keep Software Updated: Regularly patch operating systems, applications, and web browsers to close known security vulnerabilities. Enable automatic updates where possible.
    4. Strong Antivirus/Endpoint Protection: Install and maintain reputable antivirus software with real-time protection and keep its definitions updated.
    5. Firewall Configuration: Configure firewalls to block unnecessary inbound and outbound connections, particularly RDP if not critically needed, or secure it with strong passwords and MFA if used.
    6. User Education: Train users to identify phishing attempts, suspicious downloads, and the risks associated with untrusted software.
    7. Disable PowerShell/Scripting for Users: Where possible and practical, restrict or disable PowerShell execution for standard users.
    8. AppLocker/SRP (Software Restriction Policies): Implement policies to prevent execution of files from common ransomware drop locations (e.g., AppData, Temp folders).

2. Removal

  • Infection Cleanup:
    1. Isolate the Infected System: Immediately disconnect the infected computer from the network (unplug Ethernet, disable Wi-Fi) to prevent the ransomware from spreading to other devices.
    2. Identify the Ransomware: Look for the _readme.txt ransom note on the desktop or in encrypted folders. This note typically contains instructions and the contact email (e.g., [email protected], [email protected]).
    3. Boot into Safe Mode: Restart the computer in Safe Mode with Networking. This often prevents the ransomware’s executable from running automatically upon startup.
    4. Run a Full System Scan: Use a reputable, updated antivirus or anti-malware tool (e.g., Malwarebytes, Windows Defender, ESET, Sophos) to perform a full scan and remove all detected threats, including the ransomware executable and any associated malware (like password stealers – see “Other Critical Information”).
    5. Remove Persistence: Check common persistence locations (e.g., Startup folders, Registry Run keys, Scheduled Tasks) for any entries related to the ransomware and remove them. Tools like Autoruns can assist.
    6. Change All Passwords: If any password stealers were present (common with STOP/Djvu), change all passwords for online accounts (email, banking, social media, cloud services) from an uninfected device.

3. File Decryption & Recovery

  • Recovery Feasibility:
    • Possible for “Offline” Keys: Decryption is possible for files encrypted with an “offline” key. This happens when the ransomware fails to communicate with its command-and-control (C2) server during encryption, forcing it to use a hardcoded, offline encryption key. Security researchers often manage to recover these offline keys, allowing for decryption.
    • Not Possible for “Online” Keys: Decryption is not possible for files encrypted with “online” keys. These are unique session keys generated by the C2 server for each victim, and without the attackers’ private key, they cannot be decrypted. The majority of STOP/Djvu infections use online keys.
  • Methods/Tools Available:
    • Emsisoft Decryptor for STOP/Djvu: This is the primary tool for decrypting STOP/Djvu files. It’s developed by Emsisoft in collaboration with Michael Gillespie (MalwareHunterTeam).
      • How it works: You provide encrypted and original (unencrypted) files. The tool attempts to match them to known offline keys. If a match is found, it can decrypt files encrypted with that specific offline key.
      • Limitations: It cannot decrypt files encrypted with an “online” key unless that specific online key has been compromised or released by the attackers.
    • No More Ransom Project: Visit nomoreransom.org and use their “Crypto Sheriff” tool. Upload the ransom note and an encrypted file; it can help identify the ransomware and link you to available decryptors if one exists.
    • Data Recovery Software: For unencrypted shadow copies or deleted original files, data recovery software (e.g., PhotoRec, Recuva) might retrieve some data, but this is often unreliable after a ransomware attack.
  • Essential Tools/Patches:
    • Emsisoft Decryptor for STOP/Djvu: Crucial for decryption attempts.
    • Reputable Antivirus/Anti-malware Software: For initial removal.
    • Operating System Updates: Keep Windows/macOS/Linux fully patched.
    • Browser Updates: Keep web browsers (Chrome, Firefox, Edge) updated to the latest versions.
    • Microsoft .NET Framework: Ensure it’s updated, as some tools may rely on it.

4. Other Critical Information

  • Additional Precautions:
    • Information Stealer Component: A significant distinguishing characteristic of many STOP/Djvu variants (including those with @inbox.ru contacts) is that they often drop additional malware, most commonly a password stealer (like Vidar, Azorult, RedLine Stealer). This stealer is designed to exfiltrate sensitive data such as:
      • Saved browser passwords and cookies
      • Cryptocurrency wallet data
      • Files from desktop/documents folders
      • VPN client credentials
      • FTP client credentials
      • Other sensitive information
      • This means even if you recover your files, your personal data and online accounts might be compromised. Immediate password changes for all online accounts (from a clean device) are critically important.
    • Ransom Note: The _readme.txt ransom note is consistently used across nearly all STOP/Djvu variants, making it a reliable indicator of this family. It typically instructs victims to contact the provided email (e.g., [email protected]) for payment details, offering a “discount” if contacted within 72 hours.
    • False Claims: The ransom note often claims that paying the ransom is the “only way” to recover files, which is not always true, especially for offline key infections.
  • Broader Impact:
    • Widespread Consumer Impact: Due to its reliance on easily accessible vectors like pirated software, STOP/Djvu has disproportionately affected individual users and small, unprotected businesses worldwide. This leads to significant personal data loss, financial strain, and psychological distress.
    • Financial Gain for Attackers: The sheer volume of infections, even with relatively low ransom demands (typically $490-$980 USD), makes it highly lucrative for the threat actors.
    • Evolutionary Nature: The constant release of new variants with minor code changes and different file extensions/email contacts makes it challenging for security researchers to keep up with decryptor development for every online key.
    • Undermining Security Trust: The prevalence of this ransomware, particularly via cracked software, contributes to a general distrust in online downloads and highlights the risks of digital piracy.