1c

This resource provides a detailed technical breakdown and practical recovery strategies for the ransomware variant identified by the file extension .1c. It’s important to note that the .1c extension is commonly associated with a variant of the STOP/Djvu ransomware family, a highly prolific and constantly evolving threat.

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Technical Breakdown:

1. File Extension & Renaming Patterns

• Confirmation of File Extension: The ransomware appends the exact file extension .1c to encrypted files.
• Renaming Convention: When a file is encrypted, its original name is typically preserved, but the .1c extension is added to the end. For example, document.docx would become document.docx.1c, and photo.jpg would become photo.jpg.1c. In some cases, an additional random string might be inserted before the .1c extension, e.g., document.docx.[random_string].1c.
  The ransomware also typically drops a ransom note in each folder containing encrypted files, usually named _readme.txt.

2. Detection & Outbreak Timeline

• Approximate Start Date/Period: While the STOP/Djvu ransomware family itself has been active since at least late 2018, specific variants like the one using the .1c extension emerge as part of its continuous evolution. The .1c variant would have appeared within this broader timeline, as new extensions are regularly introduced by the threat actors behind STOP/Djvu. It has been observed in the wild for a significant period.

3. Primary Attack Vectors

• Propagation Mechanisms: The STOP/Djvu family, including the .1c variant, primarily relies on the following propagation mechanisms:
  • Cracked Software/Software Activators: This is a very common vector. Users download compromised cracks, key generators, or pirated software installers from dubious websites (e.g., torrent sites, free software download sites), which secretly contain the ransomware payload.
  • Bundled Downloads: Malicious software is often bundled with seemingly legitimate freeware, shareware, or online game installers.
  • Malicious Websites & Drive-by Downloads: Visiting compromised or malicious websites can sometimes trigger an automatic download of the ransomware.
  • Phishing Campaigns (Less Common for Djvu): While less prevalent than for some other ransomware, phishing emails with malicious attachments or links could also be used to deliver the payload.
  • Fake Updates: Users might be tricked into downloading fake software updates (e.g., for Flash Player, Java) that are actually ransomware installers.
  • Malvertising: Malicious advertisements on legitimate websites redirect users to pages hosting the ransomware.

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Remediation & Recovery Strategies:

1. Prevention

• Proactive Measures:
  • Robust Backups: Implement a 3-2-1 backup strategy (3 copies of data, 2 different media types, 1 offsite/offline copy). Regularly test your backup restoration process. This is the single most important defense against ransomware.
  • Software Updates & Patch Management: Keep your operating system, applications, and antivirus software up-to-date with the latest security patches. Many ransomware attacks exploit known vulnerabilities.
  • Strong Antivirus/Endpoint Detection & Response (EDR): Deploy and maintain reputable antivirus or EDR solutions with real-time protection and behavioral analysis capabilities.
  • User Education: Train users to identify and avoid suspicious emails, unsolicited downloads, and untrusted websites. Emphasize the dangers of cracked software.
  • Network Segmentation: Isolate critical systems and data to limit the spread of ransomware in case of a breach.
  • Disable Unnecessary Services: Turn off services like SMBv1, RDP, and PowerShell if not explicitly required, or secure them with strong authentication and network access controls.
  • Least Privilege Principle: Grant users and applications only the minimum necessary permissions to perform their tasks.
  • Application Whitelisting: Allow only approved applications to run on your systems.

2. Removal

• Infection Cleanup:
  1. Isolate the Infected System: Immediately disconnect the infected computer from the network (unplug Ethernet cable, disable Wi-Fi) to prevent further spread.
  2. Identify the Threat: Use an updated antivirus/anti-malware scanner (e.g., Malwarebytes, ESET, Sophos, Microsoft Defender) to perform a full system scan.
  3. Remove Malicious Files: Allow the security software to quarantine or delete detected ransomware components.
  4. Check for Persistence: Manually check common persistence locations (e.g., Startup folders, Registry Run keys, Scheduled Tasks) for any remaining malicious entries.
  5. Change Credentials: After ensuring the system is clean, change all passwords, especially those for accounts that were logged in or stored on the infected machine.
  6. Review System Restore Points: The ransomware might delete Volume Shadow Copies. Check if any viable restore points exist from before the infection.

3. File Decryption & Recovery

• Recovery Feasibility: Decrypting files encrypted by the .1c variant of STOP/Djvu ransomware is challenging, and its success largely depends on whether your files were encrypted using an “online” or “offline” key:
  • Online Keys: If the ransomware successfully connected to its command-and-control server during encryption, it used a unique “online key” specific to your machine. Decryption is generally not possible without paying the ransom or a major law enforcement breakthrough. There is no public decryptor for files encrypted with online keys.
  • Offline Keys: In rare cases (e.g., if the C2 server was unreachable), the ransomware might use a generic “offline key.” If this happens, decryption might be possible using tools like the Emsisoft STOP/Djvu Decryptor. This tool checks if your files were encrypted with an offline key and attempts to decrypt them if a matching key is known.
• Essential Tools/Patches:
  • Emsisoft STOP/Djvu Decryptor: This is the primary tool to attempt decryption for STOP/Djvu variants. It requires at least one original (unencrypted) and its encrypted counterpart to work best, but can sometimes recover files with only encrypted ones if an offline key was used.
  • Reputable Antivirus/Anti-malware Software: Crucial for initial prevention and post-infection cleanup.
  • Data Backup & Recovery Solutions: Essential for restoring data from clean backups.
  • Operating System Patches: Ensure Windows is fully updated to mitigate common exploit vectors.
  • Network Monitoring Tools: To detect unusual network activity that might indicate ransomware communication or spread.

4. Other Critical Information

• Additional Precautions: The STOP/Djvu family, including the .1c variant, often bundles information-stealing malware (e.g., Vidar, Azorult, RedLine Stealer) with the ransomware payload. This means that even if you don’t pay the ransom and restore from backups, your sensitive data (passwords, cryptocurrency wallets, browser data, documents) might already have been exfiltrated by the attackers. It’s crucial to assume data compromise and take steps like changing all passwords.
• Broader Impact: The widespread nature of STOP/Djvu variants (due to their common distribution through pirated software) means they affect a vast number of individual users and small businesses globally. The .1c variant contributes to this significant impact, leading to:
  • Significant Data Loss: For victims without adequate backups or successful decryption.
  • Financial Costs: Ransom demands typically range from hundreds to thousands of dollars, often doubling if not paid within a specific timeframe.
  • Business Disruption: For organizations, encryption can halt operations, leading to lost productivity and revenue.
  • Reputational Damage: Especially for businesses handling sensitive customer data.
  • Risk of Further Attacks: The presence of infostealers means victims are vulnerable to follow-on attacks using their stolen credentials.

Always report ransomware incidents to your local law enforcement or cybersecurity authorities to contribute to broader efforts to combat cybercrime.