File Upload Vulnerability Checklist

Welcome to our introductory guide to file upload security tailored for beginners! File uploads are ubiquitous in modern websites, enabling users to share a variety of content such as photos and documents. However, safeguarding these uploads is essential to shield both your users and your website from potential malicious attacks.

In this guide, we will lead you through the fundamentals of file upload security testing. From verifying file extensions to thwarting directory traversal attacks, we will cover essential techniques to bolster the security of your website. Let’s delve into the strategies for defending against common vulnerabilities and fortifying your online platform.

1. Assess handling of various file extensions:
— Experiment with uploading files with extensions such as .txt, .pdf, .jpg to ensure the application securely manages them.

2. Validate the implementation of regular expressions (regex) for proper validation:
— Test uploading files with altered extensions (e.g., renaming .exe files as .jpg) to validate if regex patterns effectively thwart such deceptive inputs.

3. Evaluate the handling of .svg files and potential security risks:
— Upload .svg files containing malicious JavaScript code and evaluate if the application effectively sanitizes them to prevent XSS attacks.

4. Investigate content type manipulation to circumvent file type restrictions:
— Modify the content-type header from “text/plain” to “image/jpeg” and attempt to upload a malicious file.

5. Implement magic bytes to bypass validation:
— Append PHP script tags to a JPEG file and assess if the application detects and rejects the file appropriately.

6. Assess handling of file sizes:
— Upload files of varying sizes, including excessively large ones, to evaluate how the application manages them and responds.

7. Analyze the handling of files with executable extensions:
— Attempt to upload files with executable extensions like .exe and verify if the application rejects them to prevent potential security vulnerabilities.

8. Check for null byte injection vulnerabilities in file names:
— Upload a file named “malicious%00.jpg” containing null bytes and verify if the application handles it securely.

9. Test for vulnerabilities related to special characters preceding the file extension:
— Upload a file named “malicious<script>.jpg” containing special characters and evaluate if the application handles them properly.

10. Validate processing of EXIF data in files:
— Upload an image with crafted EXIF metadata and verify if the application processes it securely without compromising user privacy.

11. Assess handling of Windows 8.3 notation for file names:
— Attempt to upload a file named “malici~1.jpg” using Windows 8.3 notation and verify if the application handles it securely.

12. Verify correct handling of characters converted during file upload:
— Upload a file named “malicious&.jpg” containing special characters and ensure the application sanitizes them correctly.

13. Test for directory traversal vulnerabilities:
— Attempt to access files outside the intended directory and check if the application prevents directory traversal attacks.

14. Investigate potential vulnerabilities related to overwriting server configuration files:
— Attempt to upload a file named “web.config” to overwrite server configuration and assess if the application prevents such actions.

15. Test for file upload race conditions:
— Simultaneously upload multiple files and assess if the application handles them without data corruption or system instability.

16. Explore specific vulnerabilities related to the server environment and libraries:
— Investigate known vulnerabilities in server environments and libraries like PHP’s GD or ImageMagick to identify and mitigate potential risks.

17. Evaluate susceptibility to denial-of-service (DoS) vulnerabilities:
— Attempt to overwhelm the system with numerous concurrent uploads or excessively large files to assess if the application is susceptible to DoS attacks.

In conclusion, this checklist underscores the multifaceted nature of maintaining secure file uploads. It emphasizes the importance of vigilance and proactive measures. From validating file types to mitigating threats like DoS attacks, each point contributes to fortifying websites against emerging dangers. Adhering to these guidelines and staying abreast of new risks fosters user trust, safeguards critical data, and preserves online system integrity. Proactive security measures are paramount in fortifying resilience against evolving cyber threats.