@airmail.cc

[Content by Gemini 2.5]

The ransomware variant identified by the file extension @airmail.cc is most commonly associated with the highly prevalent STOP/Djvu ransomware family. While @airmail.cc might not be the literal file extension appended to every file, it is a prominent contact email address frequently used by various iterations of STOP/Djvu ransomware in their ransom notes (_readme.txt). This email address serves as a primary identifier for specific campaigns or sub-variants within this family.

Understanding this context is crucial, as the characteristics and recovery methods for @airmail.cc are largely consistent with the broader STOP/Djvu family’s behavior.

Technical Breakdown:

1. File Extension & Renaming Patterns

  • Confirmation of File Extension:
    While @airmail.cc itself is primarily a contact email address found in the ransom note, file extensions encrypted by variants using this email follow the typical STOP/Djvu pattern. This pattern involves appending a unique, often four-character, random extension followed by an ID and sometimes the email or related string.

    • Common Pattern: [original_filename].[original_extension].[4-character_random_extension]
      • Example: document.docx.lqqw, photo.jpg.rloo, archive.zip.qwer
    • ID Inclusion: Files might also have an ID appended, often in the format: .[original_extension].id[YOUR_ID].[4-character_random_extension]
      • Example: document.docx.id1A2B3C4D.lqqw
    • Direct Incorporation (Less Common but Possible): In some rarer instances or specific sub-variants, the email-related string might appear directly in the appended extension, for example, .[original_extension].id[YOUR_ID][email protected] or .[original_extension].[4-character_random_extension].airmail. However, the primary identifier for @airmail.cc variants of STOP/Djvu is the presence of this email in the _readme.txt ransom note, which always accompanies the encrypted files.

  • Renaming Convention:
    The ransomware renames files by appending its unique extension to every encrypted file. For instance, myphoto.jpg might become myphoto.jpg.lqqw. A ransom note, typically named _readme.txt, is dropped in every folder containing encrypted files, providing instructions for payment and contact information (which would include [email protected], [email protected], or similar @airmail.cc variants).

2. Detection & Outbreak Timeline

  • Approximate Start Date/Period:
    The STOP/Djvu ransomware family, which frequently uses email addresses like @airmail.cc for contact, has been highly active and widespread since late 2018 and continues to be one of the most prolific ransomware threats targeting individual users. Variants using specific email addresses like @airmail.cc emerge as part of ongoing campaigns within this established family. Its prevalence peaked in 2019-2021 and remains significant.

3. Primary Attack Vectors

The STOP/Djvu family (and thus variants using @airmail.cc) primarily targets individual users rather than large enterprises, and its propagation methods reflect this:

  • Bundled Software & Freeware: The most common vector. Users download seemingly legitimate software (e.g., cracked versions of paid software, key generators, pirated movies/music, fake installers for games) from untrustworthy websites. The ransomware is bundled silently within these downloads.
  • Malicious Websites & Drive-by Downloads: Visiting compromised websites or malicious advertising networks can sometimes lead to drive-by downloads where the malware is automatically downloaded without user interaction, often disguised as legitimate files.
  • Fake Software Updates: Pop-ups or alerts promoting fake updates for popular software (e.g., Flash Player, Java, web browsers) can trick users into downloading the ransomware.
  • Email Phishing Campaigns: While less common for STOP/Djvu than for other ransomware families targeting businesses, some variants may spread through phishing emails containing malicious attachments or links.
  • Weak RDP/SMB Exploitation: Less typical for STOP/Djvu compared to other ransomware like Ryuk or Conti, but not entirely impossible if a system is highly vulnerable and exposed. However, the primary focus is on user-initiated downloads.

Remediation & Recovery Strategies:

1. Prevention

  • Proactive Measures:
    • Data Backup: Implement a robust backup strategy following the 3-2-1 rule (3 copies, 2 different media types, 1 offsite). Regularly back up critical data to an external drive or cloud storage that is disconnected from the network when not in use.
    • Software Updates: Keep your operating system, web browsers, antivirus software, and all other applications fully updated with the latest security patches. Vulnerabilities are frequently exploited.
    • Antivirus/Anti-Malware: Use a reputable, up-to-date antivirus/anti-malware solution with real-time protection.
    • Firewall: Enable and properly configure your operating system’s firewall.
    • User Account Control (UAC): Keep UAC enabled on Windows systems to prompt for administrative privileges before significant system changes.
    • Email Vigilance: Be cautious of unsolicited emails, especially those with attachments or links. Verify the sender’s identity before opening anything.
    • Safe Browsing Habits: Avoid visiting suspicious websites, downloading files from untrusted sources, or using “cracked” software. These are primary infection vectors.
    • Disable Macros: Disable macros in Microsoft Office files by default, or only enable them for trusted documents.
    • Ad Blockers: Use browser extensions that block malicious ads and scripts to prevent drive-by downloads.

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 to other devices.
    2. Boot into Safe Mode: Restart your computer in Safe Mode with Networking. This often prevents the ransomware processes from fully launching and interfering with removal tools.
    3. Run a Full System Scan: Use your reputable antivirus/anti-malware software (e.g., Malwarebytes, Windows Defender, ESET, Bitdefender) to perform a full system scan. Ensure the definitions are up-to-date. The scan should detect and quarantine/remove the ransomware executable and any associated malicious files.
    4. Check for Persistence: Manually check common persistence locations (e.g., Msconfig for startup items, Task Scheduler, Registry Editor for Run keys) for any suspicious entries that might re-launch the malware. Remove any found, but only if you are confident they are malicious.
    5. Clean Temp Files: Delete temporary files (%temp%, C:\Windows\Temp) which might contain residual malware components.
    6. Change Passwords: Once the system is clean, change all passwords for online accounts accessed from the infected system, especially for email, banking, and cloud services. Consider changing network device passwords if compromised.

3. File Decryption & Recovery

  • Recovery Feasibility:
    Decryption feasibility for STOP/Djvu variants (including those using @airmail.cc contacts) largely depends on whether an online key or an offline key was used during encryption.

    • Online Key: If the ransomware was able to connect to its command-and-control (C2) server during encryption, it uses a unique online key for each victim. Decrypting files encrypted with an online key is generally impossible without the specific private key held by the attackers, making recovery very difficult without paying the ransom.
    • Offline Key: If the ransomware failed to connect to its C2 server, it often resorts to using a pre-determined “offline” key. Many STOP/Djvu variants share a limited set of offline keys. Files encrypted with an offline key can often be decrypted if the corresponding key has been recovered and published by security researchers.

  • Essential Tools/Patches:

    • Emsisoft Decryptor for STOP/Djvu: This is the primary and most reliable tool for decrypting files encrypted by STOP/Djvu variants. It is freely available from Emsisoft. The decryptor works by trying known offline keys and can sometimes help identify if an online key was used.
      • Note: The decryptor requires a pair of encrypted and original (unencrypted) files to determine the specific key variant, which is often difficult to provide. Failing that, it can attempt to decrypt using known offline keys. Success is not guaranteed, especially for online-encrypted files.
    • Data Recovery Software: Tools like PhotoRec, Recuva, or Disk Drill can sometimes recover deleted shadow copies or original files that were deleted before encryption occurred (as some ransomware first makes copies, encrypts them, then deletes originals). Success is highly variable.
    • System Restore & Shadow Copies: Ransomware often attempts to delete Volume Shadow Copies (vssadmin delete shadows /all /quiet) to prevent recovery. If the ransomware failed to do so, you might be able to restore previous versions of files using Windows’ built-in “Previous Versions” feature or via System Restore points. This is rare for STOP/Djvu, as it’s typically effective at deleting them.
    • Backups: The most reliable recovery method is restoring from clean, external backups.

4. Other Critical Information

  • Additional Precautions:

    • Info-stealing Malware: Many recent STOP/Djvu variants are bundled with other malicious software, most notably info-stealers like Vidar Stealer, RedLine Stealer, or Azorult. These steal credentials, cryptocurrency wallets, browser data, and other sensitive information. Even if you manage to decrypt your files, assume your personal information has been compromised. Change all important passwords immediately from a clean device.
    • Ransom Note: The ransom note (_readme.txt) typically provides two email addresses for contact and negotiation (e.g., [email protected] and [email protected]), often with an offer of a 50% discount if contacted within 72 hours. It’s generally advised not to pay the ransom, as there’s no guarantee of decryption, and it funds criminal activity.
    • ID File: The ransomware typically drops an info.txt or PersonalID.txt file containing the victim’s unique ID and sometimes the version of the ransomware.

  • Broader Impact:
    The STOP/Djvu family, which includes variants using @airmail.cc, has had a massive global impact, primarily affecting individual users and small businesses due to its reliance on common software piracy and freeware distribution channels. Its high volume and relatively unsophisticated attack vectors make it a constant threat to less technically savvy users. The addition of info-stealing capabilities in recent versions significantly elevates the risk beyond just file encryption, leading to potential identity theft and financial fraud.