#howtorecover.txt

[Content by Gemini 2.5]

This document addresses the ransomware variant identified by the file extension #howtorecover.txt. It is crucial to clarify at the outset that #howtorecover.txt is almost certainly the name of the ransom note file dropped by the ransomware, rather than the file extension appended to encrypted files. Ransomware typically appends a unique, often seemingly random, string (e.g., .djvu, .mado, .qbaa, .locked) to the end of encrypted file names.

Based on the characteristic naming convention of the ransom note (e.g., _howtorecover.txt, HOW_TO_RECOVER.txt, or containing instructions to look for such a file), this analysis will focus on the highly prevalent STOP/Djvu ransomware family, which is notorious for dropping ransom notes with similar names, commonly _readme.txt, and has a history of adapting its strategies.

Technical Breakdown:

1. File Extension & Renaming Patterns

  • Confirmation of File Extension:
    As stated, #howtorecover.txt (or variations like _howtorecover.txt, HOW_TO_RECOVER.txt) is not the encrypted file extension. It is the name of the ransom note file placed in every folder containing encrypted files, and often on the desktop.
    The actual file extensions appended to encrypted files by STOP/Djvu ransomware variants are highly diverse and frequently change with new iterations. Common examples include .djvu, .mado, .qbaa, .karl, .gero, .qoop, .sijr, .nlah, .maas, and hundreds more. These extensions are typically 4-character strings.

  • Renaming Convention:
    The ransomware renames files by appending its unique extension to the original filename. The pattern is:
    original_filename.original_extension.[ransomware_extension]
    For example: document.docx might become document.docx.mado or photo.jpg might become photo.jpg.qbaa.

2. Detection & Outbreak Timeline

  • Approximate Start Date/Period:
    The STOP/Djvu ransomware family first emerged around late 2017 to early 2018. It quickly rose to prominence and has remained one of the most prolific and widespread ransomware variants, continuously evolving with new versions released almost daily. Its activity peaked significantly throughout 2018, 2019, and continues to be a major threat into the present day.

3. Primary Attack Vectors

  • Propagation Mechanisms:
    STOP/Djvu primarily relies on deceptive distribution methods targeting individual users and small businesses rather than exploiting enterprise-level vulnerabilities. Its main propagation mechanisms include:
    • Malicious Software Bundles: This is the most common vector. The ransomware is often bundled with pirated software, cracked applications, key generators (keygens), software activators, and illegal installers downloaded from torrent sites, file-sharing platforms, or untrustworthy freeware sites. When the user attempts to install or activate the desired software, the ransomware silently executes in the background.
    • Phishing Campaigns: While less common than software bundles for Djvu, generic phishing emails delivering malicious attachments (e.g., seemingly legitimate invoices, shipping notifications, or resumes with embedded macros or hidden scripts) can also be used.
    • Malvertising: Advertisements on legitimate or illegitimate websites that redirect users to compromised sites or directly download malicious payloads.
    • Fake Updates: Prompts for fake software updates (e.g., Flash Player, Java) that, when clicked, download the ransomware.
    • Compromised Websites: Drive-by downloads from compromised websites, though less frequent.
    • Remote Desktop Protocol (RDP) Exploits: While not a primary vector for initial infection of STOP/Djvu, poorly secured RDP connections can be exploited by attackers to manually deploy this ransomware once access is gained. However, it’s not its inherent spread mechanism.

Remediation & Recovery Strategies:

1. Prevention

  • Proactive Measures:
    1. Regular Backups: Implement a robust 3-2-1 backup strategy (3 copies of data, on 2 different media, with 1 copy offsite/offline). Crucially, ensure backups are isolated from the network to prevent them from being encrypted.
    2. Software Updates: Keep your operating system (Windows), applications, and security software fully updated with the latest patches. This mitigates vulnerabilities exploited by ransomware.
    3. Antivirus/Anti-malware Software: Install and maintain reputable antivirus/anti-malware software with real-time protection enabled. Ensure definitions are updated daily.
    4. User Education: Train users to identify phishing emails, suspicious links, and avoid downloading pirated software, cracked tools, or executables from untrusted sources.
    5. Disable Macros: Configure Microsoft Office to disable macros by default, or only allow digitally signed macros from trusted publishers.
    6. Strong Passwords & MFA: Use strong, unique passwords for all accounts and enable Multi-Factor Authentication (MFA) wherever possible, especially for remote access services like RDP.
    7. Firewall Configuration: Employ a robust firewall to block unauthorized inbound and outbound connections.
    8. Principle of Least Privilege: Limit user permissions to only what is necessary for their role.
    9. Disable SMBv1: Disable Server Message Block version 1 (SMBv1) protocol, as it has known vulnerabilities (though less relevant for Djvu’s typical initial infection vector, it’s good general practice).

2. Removal

  • Infection Cleanup:
    1. Isolate the Infected System: Immediately disconnect the infected computer from the network (unplug Ethernet cable, disable Wi-Fi). This prevents further spread to other devices.
    2. Identify and Terminate Processes: Use Task Manager (Ctrl+Shift+Esc) to look for suspicious processes. STOP/Djvu often creates a malicious executable in %AppData% or %LocalAppData%.
    3. Boot into Safe Mode: Restart the computer in Safe Mode with Networking (if necessary, for downloading tools) to prevent the ransomware from fully executing.
    4. Run a Full System Scan: Use a reputable, updated antivirus/anti-malware suite (e.g., Malwarebytes, Windows Defender Offline Scan, ESET, Bitdefender) to perform a deep scan and remove all detected threats. Some ransomware components might resist removal in normal mode.
    5. Remove Persistence: Check common startup locations (MSConfig, Task Scheduler, Registry Editor HKEYCURRENTUSER\Software\Microsoft\Windows\CurrentVersion\Run and HKEYLOCALMACHINE\Software\Microsoft\Windows\CurrentVersion\Run) for entries related to the ransomware and delete them.
    6. Delete Malicious Files: Manually delete any identified ransomware executables or associated files. Be cautious if you are unsure, as deleting critical system files can cause instability.
    7. Change All Passwords: If the system was connected to the internet, assume credentials might have been compromised and change all passwords for online accounts (email, banking, social media, etc.) from a clean, uninfected device.

3. File Decryption & Recovery

  • Recovery Feasibility:
    The feasibility of decrypting files encrypted by STOP/Djvu ransomware varies significantly depending on the specific variant and whether an “online key” or “offline key” was used during encryption.

    • Online Keys: Most modern STOP/Djvu variants use “online keys.” This means a unique encryption key is generated for each victim’s machine and transmitted to the attacker’s server. Without this specific key, decryption is virtually impossible without paying the ransom.
    • Offline Keys: In some cases, if the ransomware fails to connect to its command-and-control server, it falls back to using an “offline key” – a default, hardcoded key. If an offline key was used, there is a chance that a decryptor might work, especially if that specific offline key has been recovered by security researchers.
    • Emsisoft Decryptor: Emsisoft, in collaboration with the No More Ransom project, provides a free decryptor for many STOP/Djvu variants. However, this tool is primarily effective for variants that used offline keys or for which online keys have been publicly recovered. It is crucial to try this tool, but understand it may not work for the newest online-key variants.

  • Essential Tools/Patches:

    • Emsisoft Decryptor for STOP/Djvu Ransomware: Download from the Emsisoft website or No More Ransom project.
    • Reputable Antivirus/Anti-malware Software: For detection and removal (e.g., Malwarebytes, Windows Defender, Bitdefender, ESET).
    • Backup Software: If you have uninfected backups, this is the primary and most reliable recovery method.
    • Shadow Explorer: A tool to browse and restore files from Volume Shadow Copies, which the ransomware often tries to delete. However, many Djvu variants specifically target and delete shadow copies using vssadmin.exe delete shadows /all /quiet.
    • File Recovery Software: Tools like PhotoRec or Recuva might recover older versions of files if the ransomware encrypted them and then deleted the originals, but success rates are generally low after ransomware attacks.

4. Other Critical Information

  • Additional Precautions:

    • DO NOT PAY THE RANSOM: While tempting, paying the ransom does not guarantee decryption and funds criminal activities, encouraging more attacks.
    • Offline vs. Online Keys: Be aware that decryptors for STOP/Djvu are most effective for older variants or those encrypted with offline keys. New variants are constantly emerging, making decryption without the attackers’ key exceedingly difficult.
    • Beware of Fake Decryptors: There are many scams promising decryption tools that are themselves malware. Only use tools from trusted security vendors (e.g., Emsisoft, No More Ransom).
    • Patience and Monitoring: Security researchers constantly work to find new vulnerabilities or recover keys. Regularly check the Emsisoft and No More Ransom sites for updates.

  • Broader Impact:

    • Massive Scale: STOP/Djvu is one of the most prolific ransomware families globally, affecting hundreds of thousands of individual users and small to medium-sized businesses. Its high volume of attacks contributes significantly to the overall ransomware landscape.
    • Financial Impact: Victims often lose irreplaceable data and incur significant costs attempting recovery, whether through professional services or, unfortunately, paying the ransom.
    • Psychological Distress: The loss of personal photos, documents, and business-critical data causes immense stress and disruption.
    • Economic Disruption: While not targeting critical infrastructure like some larger ransomware gangs, the cumulative impact of widespread individual and small business infections leads to substantial economic disruption.
    • Constant Evolution: The developers behind STOP/Djvu are very active, frequently releasing new variants with updated encryption methods and file extensions, making ongoing decryption efforts challenging. This constant evolution is a defining characteristic and a major hurdle for recovery.