6.LFI-and-file-uploads

Key Takeaways:

• LFI and File Upload Synergy:

  • File uploads, even seemingly secure ones, can be leveraged with LFI.

  • The LFI vulnerability is the primary attack vector.

  • File uploads provide a way to place malicious code on the server.

• Image Upload Technique:

  • Crafting a malicious image file with embedded PHP code.

  • Using valid image magic bytes and extensions.

  • Uploading the malicious image through a standard upload form.

  • Retrieving the uploaded file's path.

  • Including the uploaded file via LFI to execute the embedded code.

• Zip Upload Technique:

  • Creating a zip archive containing a PHP web shell.

  • Uploading the zip archive.

  • Using the zip:// wrapper to include the zipped PHP script.

  • Good to note that this method relies on the zip extension being enabled.

• Phar Upload Technique:

  • Creating a phar archive with embedded PHP code.

  • Uploading the phar archive.

  • Using the phar:// wrapper to include and execute the embedded code.

  • Again, good to note that this method relies on the phar extension being enabled.

• Importance of Code Execution:

  • The LFI vulnerability must allow code execution for these techniques to work.

  • Functions like include() and require() are vulnerable.

• Path Discovery:

  • The explanation correctly states that the location of the uploaded file must be found. Methods of finding the location are covered.

Additional Considerations:

• Real-World Scenarios:

  • Attackers often use more sophisticated web shells and payloads.

  • WAFs and other security measures can hinder these attacks.

  • Defense in depth is very important.

• File Type Validation:

  • While the explanation focuses on bypassing extension checks, content-type validation is also common.

  • Attackers may use techniques to bypass content-type checks.

• Security Best Practices:

  • Proper input validation and sanitization are crucial.

  • Restricting file uploads to specific file types and sizes.

  • Storing uploaded files outside the web root.

  • Disabling or restricting file inclusion functions.

• PHP Configuration:

  • The zip://, and phar:// wrappers rely on php extensions. Disabling unneeded extensions is a good security practice.

• Magic Bytes:

  • Understanding magic bytes is essential for crafting malicious files.

  • Tools like file can help identify file types and magic bytes.

• Defense in Depth:

  • Combining multiple security measures is essential.

  • Regular security audits and penetration testing.