1dec

[Content by Gemini 2.5]

The .1dec file extension is characteristic of a variant belonging to the prolific STOP/Djvu ransomware family. This family is one of the most active strains targeting individual users and small businesses, constantly evolving with new extensions and minor code changes. Below is a detailed resource concerning this variant.

Technical Breakdown:

1. File Extension & Renaming Patterns

  • Confirmation of File Extension: The exact file extension used by this ransomware variant is .1dec.
  • Renaming Convention: When a file is encrypted by this variant, its original filename is appended with the .1dec extension. The typical renaming pattern is:
    • original_filename.extension.1dec
    • Example: A file named document.docx would become document.docx.1dec. An image photo.jpg would become photo.jpg.1dec.

2. Detection & Outbreak Timeline

  • Approximate Start Date/Period: Variants of the STOP/Djvu ransomware family (including those using extensions like .1dec) have been consistently active since late 2018/early 2019. New extensions are frequently observed, sometimes appearing weekly or even daily, as the developers release new versions to evade detection. The specific .1dec variant would have appeared as one of the many new iterations within this ongoing campaign.

3. Primary Attack Vectors

STOP/Djvu ransomware, including the .1dec variant, predominantly relies on deceptive distribution methods that exploit user trust and lack of vigilance:

  • Cracked Software/Software Bundles: This is the most prevalent method. Users often download pirated software, key generators, software activators (e.g., for Windows or Adobe products), or illegal software cracks from dubious websites. These downloads are bundled with or contain the ransomware payload.
  • Fake Software Updates: Malicious websites or pop-ups may trick users into downloading fake updates for legitimate software (e.g., Flash Player, Java, web browsers), which in reality are ransomware installers.
  • Malicious Downloads/Installers: The ransomware can be disguised within seemingly legitimate installers for various applications downloaded from unofficial sources.
  • Malvertising: Users visiting compromised websites or sites serving malicious advertisements can be redirected to pages that push the ransomware payload disguised as something else.
  • Email Phishing Campaigns: Less common for STOP/Djvu than for some other ransomware strains, but still possible. Malicious attachments (e.g., infected documents, executables) or links within phishing emails can lead to infection.
  • Fake Tech Support Scams: In some cases, victims might be tricked into downloading and running the ransomware as part of a fake tech support scenario.

Remediation & Recovery Strategies:

1. Prevention

Proactive measures are the most effective defense against ransomware like the .1dec variant:

  • Regular Data Backups: Implement a robust backup strategy following the 3-2-1 rule (3 copies, 2 different media types, 1 off-site). Ensure backups are isolated from the network to prevent them from being encrypted.
  • Use Reputable Antivirus/Anti-malware Software: Keep your security software updated and perform regular scans. Enable real-time protection.
  • Software Updates: Keep your operating system, web browsers, and all installed applications patched and updated to close known vulnerabilities.
  • User Education: Educate users about the dangers of downloading software from unofficial sources, clicking suspicious links, or opening attachments from unknown senders.
  • Strong Passwords & MFA: Use strong, unique passwords for all accounts, especially RDP and network shares. Implement Multi-Factor Authentication (MFA) where possible.
  • Firewall Configuration: Configure your firewall to block unnecessary incoming connections and restrict access to critical services.
  • Disable Unnecessary Services: Disable SMBv1 and other outdated or unneeded services.

2. Removal

Once infected, the priority is to stop the encryption process and remove the threat:

  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 Ransom Note: Look for the ransom note, typically named _readme.txt, usually found on the desktop and in folders containing encrypted files. This note often provides instructions and the contact email for the attackers. Do NOT pay the ransom.
  3. Boot into Safe Mode: Restart the computer in Safe Mode with Networking. This loads only essential services and drivers, making it easier for security software to operate without interference from the ransomware’s persistence mechanisms.
  4. Perform a Full System Scan: Use a reputable antivirus or anti-malware solution (e.g., Malwarebytes, Emsisoft Anti-Malware, reputable paid AV products) to perform a deep scan and remove all detected threats.
  5. Check for Persistence:
    • Startup Programs: Check Task Manager (Windows 10/11) or msconfig (older Windows) for suspicious entries set to run at startup.
    • Task Scheduler: Look for new, suspicious scheduled tasks that could re-launch the ransomware.
    • Registry Editor: While more advanced, some variants may add registry entries. If unsure, a clean OS reinstall is safer.
    • Hosts File: STOP/Djvu variants often modify the hosts file (C:\Windows\System32\drivers\etc\hosts) to block access to security-related websites (e.g., antivirus vendor sites) and decryption tool sites. Check this file and remove any suspicious entries.
  6. Change All Passwords: After confirming the system is clean, change all passwords used on the infected machine, especially for online services, email, and network shares.

3. File Decryption & Recovery

  • Recovery Feasibility: The possibility of decrypting files encrypted by the .1dec variant depends on whether the ransomware used an offline key or an online key.
    • Online Key: If the victim’s machine was connected to the internet during encryption, the ransomware generates a unique “online key” from its command-and-control server. Decryption with online keys is extremely difficult without the attackers’ private key.
    • Offline Key: If the victim’s machine was offline or could not connect to the C2 server during encryption, the ransomware uses a hardcoded “offline key.” Files encrypted with offline keys may be decryptable if security researchers have previously obtained and published that specific offline key.
  • Essential Tools/Methods:
    • Emsisoft STOP/Djvu Decryptor: This is the primary tool for attempting decryption. Emsisoft, in collaboration with security researchers, often collects and publishes offline keys.
      • How it works: Download the Emsisoft Decryptor for STOP/Djvu Ransomware. Run it and select the encrypted drives/folders. The tool will attempt to identify the specific variant and apply any known offline keys. It will also try to recover the pair of encrypted and original files to assist in key discovery.
      • Important Note: Even with the decryptor, success is not guaranteed, especially for files encrypted with an online key.
    • Backup Restoration: The most reliable method of file recovery is restoring from clean, uninfected backups.
    • Shadow Volume Copies: Ransomware often attempts to delete Shadow Volume Copies using commands like vssadmin.exe Delete Shadows /All /Quiet. However, in some cases, they might fail, or older copies might still exist. You can try recovering previous versions of files or folders via Windows’ built-in “Previous Versions” feature (right-click file/folder > Properties > Previous Versions).
    • Data Recovery Software: Tools like PhotoRec or Recuva might be able to recover some unencrypted files, especially if they were recently deleted or partially overwritten, but they are not effective against strongly encrypted files.

4. Other Critical Information

  • Additional Precautions:
    • Ransom Note: The _readme.txt ransom note typically demands payment in cryptocurrency (Bitcoin) and provides contact email addresses. These email addresses (e.g., [email protected], [email protected], [email protected]) often change.
    • Hosts File Modification: As mentioned, STOP/Djvu variants frequently modify the hosts file to block access to security websites, making it harder for victims to seek help or download decryption tools. Always check and clean this file.
    • Persistence: The ransomware often creates a new executable in the %AppData% or %LocalAppData% directory and sets a scheduled task or registry run key to launch it upon system startup, ensuring persistence.
    • System Information Theft: Some variants of STOP/Djvu are known to exfiltrate system information (e.g., computer name, installed software list, IP address) to the attackers’ servers before encryption begins.
  • Broader Impact:
    • Wide Accessibility: Due to its reliance on common distribution channels like cracked software sites, STOP/Djvu ransomware (including .1dec variants) affects a vast number of individual users and small businesses globally.
    • Financial Burden: Victims face the potential loss of invaluable personal data (photos, documents) if decryption is not possible, or the financial burden of paying a ransom (which is never recommended and does not guarantee recovery).
    • Reputation Damage: For businesses, a ransomware attack can lead to operational downtime, data loss, and significant reputational damage.

By understanding these technical details and implementing robust prevention and recovery strategies, individuals and organizations can significantly mitigate the risk posed by the .1dec ransomware variant and the broader STOP/Djvu family.