*[email protected]*.*

[Content by Gemini 2.5]

This document provides a comprehensive overview of the ransomware variant associated with the file extension *[email protected]*.*, which is a known variant of the STOP/Djvu ransomware family. While *[email protected]*.* might appear in the ransom note or as part of the contact email, the actual appended file extension for this specific variant is typically .default.

Technical Breakdown:

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: Files encrypted by this variant will have the .default extension appended to their original filenames. The [email protected] string serves as the contact email address listed in the ransom note.
  • Renaming Convention: The ransomware typically renames files by appending the .default extension. For example, a file named document.docx would become document.docx.default. It also drops a ransom note named _readme.txt in every folder containing encrypted files. This ransom note contains instructions for the victim, typically demanding a ransom payment in cryptocurrency and providing the [email protected] email for contact.

2. Detection & Outbreak Timeline

  • Approximate Start Date/Period: The STOP/Djvu ransomware family, to which the .default variant belongs, emerged in late 2018 and has been continuously evolving and active since. The .default variant specifically appeared in late 2019 / early 2020 as part of this ongoing evolution, maintaining a consistent presence through frequent updates and new distribution campaigns.

3. Primary Attack Vectors

The [email protected] variant, like other STOP/Djvu ransomware versions, primarily relies on the following propagation mechanisms:

  • Bundled Software & Pirated Content: This is the most common and effective method. The ransomware is frequently distributed through software cracks, key generators, pirated software installers, and other illicit downloads from unofficial websites, torrents, and file-sharing platforms. Users seeking free or cracked versions of popular software (e.g., Adobe products, Microsoft Office, games) unwittingly download and execute the ransomware payload.
  • Malvertising & Fake Updates: Less common but still observed, the ransomware can be delivered via malicious advertisements on legitimate websites (malvertising) or through fake software update prompts (e.g., Flash Player updates) that, when clicked, download the malicious payload.
  • Malicious Email Attachments (Less Common): While some ransomware uses phishing emails extensively, STOP/Djvu variants generally rely less on this method, preferring the direct download route via pirated software sites. However, general email hygiene remains crucial.
  • Drive-by Downloads: Users might inadvertently download the ransomware by visiting compromised websites that automatically initiate a download without explicit user consent.
  • Exploitation of Vulnerabilities (Rare for Djvu): Unlike some other prominent ransomware families (e.g., WannaCry exploiting EternalBlue), STOP/Djvu typically does not rely on exploiting network vulnerabilities (like SMBv1) or RDP exploits for its initial infection or lateral movement. Its primary focus is on direct user execution via deceptive downloads.

Remediation & Recovery Strategies:

1. Prevention

  • Regular Backups: Implement a robust backup strategy following the 3-2-1 rule (3 copies of data, 2 different media types, 1 offsite/cloud). Ensure backups are isolated from the network to prevent encryption.
  • Software and Operating System Updates: Keep your operating system (Windows, macOS, Linux) and all installed software (browsers, antivirus, productivity suites) up-to-date with the latest security patches.
  • Reputable Antivirus/Endpoint Detection and Response (EDR): Use a robust and regularly updated antivirus or EDR solution. Ensure real-time protection is enabled.
  • User Education: Educate users about the risks of downloading software from unofficial sources, clicking suspicious links, and opening unknown attachments. Emphasize the dangers of pirated software.
  • Firewall Configuration: Configure your firewall to block unauthorized inbound and outbound connections.
  • Disable Unnecessary Services: Disable SMBv1 and other outdated or unneeded services that could be exploited.
  • Application Whitelisting: Implement application whitelisting to prevent unauthorized executables (like ransomware payloads) from running.

2. Removal

  • Isolate Infected System: Immediately disconnect the infected computer from the network (unplug Ethernet cable, disable Wi-Fi) to prevent further spread.
  • Boot into Safe Mode: Restart the computer in Safe Mode (with Networking, if necessary for tool downloads) to prevent the ransomware processes from running automatically.
  • Run a Full System Scan: Use a reputable antivirus or anti-malware tool (e.g., Malwarebytes, ESET, Bitdefender, Microsoft Defender) to perform a comprehensive scan and remove all detected malicious files. Ensure your security software definitions are up-to-date.
  • Check for Persistence Mechanisms:
    • Examine Task Scheduler for suspicious tasks.
    • Check msconfig (Windows System Configuration) for unusual startup items.
    • Review %APPDATA%, %TEMP%, and ProgramData directories for suspicious executables.
    • Verify the hosts file (C:\Windows\System32\drivers\etc\hosts) for entries redirecting security websites. Remove any entries that block access to legitimate antivirus or update sites.
  • Delete Shadow Volume Copies: While the ransomware often attempts to delete them (vssadmin delete shadows /all /quiet), it’s good practice to verify and manually delete any remaining shadow copies if the system was restored from an earlier point, to ensure no dormant ransomware components persist. However, be aware this also deletes potential unencrypted file versions.

3. File Decryption & Recovery

  • Recovery Feasibility:
    • Direct Decryption: Decryption of files encrypted by the .default variant (and other recent STOP/Djvu versions) is highly dependent on whether an “online” or “offline” key was used during encryption.
      • Online Key: If the ransomware successfully connected to its Command & Control (C2) server, it generated a unique “online” key for your system. Decryption without paying the ransom and receiving the private key from the attackers is virtually impossible in this scenario.
      • Offline Key: If the ransomware failed to connect to its C2 server, it might have used a pre-set “offline” key. In such cases, if this “offline” key is later discovered and published by security researchers (often through analysis of victim submissions), then decryption may be possible using a specialized tool.
    • General Recommendation: The most reliable method of recovery remains restoring data from pre-infection backups.
  • Essential Tools/Patches:
    • Emsisoft Decryptor for STOP Djvu: This is the primary tool available for attempting decryption. It works by having a database of known online and offline keys. You will need to provide it with an encrypted file and its original (unencrypted) version if possible, or an encrypted and a non-encrypted file. The tool will check if a matching key is available in its database. Note: This tool’s effectiveness depends heavily on whether your specific infection used a known offline key.
    • Data Recovery Software (Low Success Rate): Tools like Recuva or PhotoRec might be able to recover older, unencrypted versions of files that were deleted by the ransomware during the encryption process, but success is highly unlikely for fully encrypted data.
    • Shadow Explorer (Limited Use): The ransomware often deletes Shadow Volume Copies. However, if it failed to do so, Shadow Explorer could potentially help restore previous versions of files. This is very rare for newer STOP/Djvu variants.

4. Other Critical Information

  • Online vs. Offline ID: A distinguishing characteristic of STOP/Djvu is its use of a victim ID, which can be found in the PersonalID field in the _readme.txt ransom note. This ID ends with either t1 (indicating an online key) or t3 (indicating an offline key). t1 IDs are generally not decryptable, while t3 IDs offer a slim chance of decryption if the specific offline key is later recovered.
  • Ransom Note: The ransomware drops a ransom note named _readme.txt in every folder where files were encrypted. This note provides instructions for paying the ransom, contact details (like [email protected]), and sometimes information about the specific variant.
  • Modification of hosts file: This variant typically modifies the hosts file (C:\Windows\System32\drivers\etc\hosts) to block access to security-related websites (e.g., antivirus vendors, cybersecurity blogs) to prevent victims from seeking help or downloading removal tools.
  • Information Stealing Component: Many STOP/Djvu variants also include an information-stealing module (often Vidar Stealer or similar) that attempts to exfiltrate sensitive data such as browser history, saved passwords, cryptocurrency wallet information, and other personal files before encryption.
  • Broader Impact: The STOP/Djvu family, including the .default variant, has a significant broader impact due to its widespread distribution via pirated software. It primarily targets individual users and small to medium-sized businesses (SMBs) who might lack robust security measures or are tempted by “free” software. Its constant evolution and the difficulty in decryption make it a persistent and costly threat, leading to significant data loss for victims who do not have adequate backups. The information-stealing aspect adds another layer of risk, potentially leading to identity theft or financial fraud.