How can you prevent security risks when uploading files?

File type mishandling can be one of the simplest ways a Hacker can gain access to a target system by simply renaming executable file types like .exe/.sh as .jpg files just to have them uploaded to the target system, It is a good practice to validate the file type through the file mimetype, make sure file are executable in their uploaded directories by removing execute permission from the both containing directories and the file itself, make sure the file is only accessible to processing script until it is fully processed, check for file size and avoid saving file to RDBMS where possible.

Implementing file size restrictions and using server-side validation techniques further bolster security measures. By setting limits on the size of uploaded files, potential vulnerabilities associated with large or oversized files can be mitigated. Additionally, conducting thorough server-side validation, including input sanitation and integrity checks, helps detect and prevent malicious file uploads that could exploit vulnerabilities in the system. Combined with regular security updates and patches, these measures contribute to a robust defense against potential security risks associated with file uploads.

Implement file type validation. Example: Profile picture should not allow .html or .php files to be uploaded. Use secure file upload libraries. Limit file size and types (example: only png upto 20kb) Rename files on upload so that the name cannot be guessed. Store files outside web root directory. Apply access controls. No execute (x) permission to any files uploaded by the user. Scan files for malwares and virus

Another side effect of limiting file sizes (or compressing) will be reduced infrastructure costs, which can be a significant factor, especially in growing products. However, we must remember that we cannot degrade user experience. Introducing a strict limit of, let’s say, 100kb on a PDF document can result in a poor user experience, preventing users from uploading valid files.

This step is crucial while working with files. Imagine a scenario where: - user uploads a PHP file to the server - the file is named ../index.php - the file ends up overwriting index.php in the parent directory - the file contains code that reads the config file, connects to the database and selects contents of the user table - Congrats! Your user table has just become public If the file was rejected or its name was sanitised, it wouldn’t happen. We also should apply correct sanitisation while loading files based on user input; otherwise, we might return the file from outside of the given scope that was not intended to be seen by others.

It is most important to store files securely. For this purpose, you can utilize Blockchain technology called IPFS (InterPlanetary File System). IPFS allows you to store files securely using content-based hashing techniques. In this system, you obtain one hash generated through the content of the file. IPFS does not store your file at one location; instead, it divides the file into smaller parts and stores them in many blockchain nodes around the world. If any file is changed, its hash is also changed due to content-based hashing. Therefore, it is not possible to tamper with the file without detection.

These days, storage is getting cheap; file storage such as AWS S3 or Azure Blob Service can offer both significant cost savings as well as increased security. File storage services provide a broad range of functionality, such as: - backups and versioning - access policies - separation of user-submitted content from the rest of your application - API access for most of the mainstream languages It might seem like an unnecessary overhead; however, if you consider all the hardening you’d have to do to make your filesystems secure and correctly separated, it’s probably less effort.

Depending on the type of application and file hosting solution chosen, it might be safer to scan them before writing anything to the file system. There are also third-party services that can be used for malware scanning. Many of those are coming as an API that you can submit files to scan to. Consider using isolated environments for storing files to ensure that even if someone uploads a malicious file, it won’t affect the rest of your infrastructure.

Following only one of these approaches won’t offer you a sufficient level of security. Make sure you implement the Swiss cheese approach (pro tip: Google this term if you’re not familiar with it), as security can only be improved by implementing multiple layers of defence - and even then, it cannot be guaranteed. Educate your users, harden your systems, and use the right tools, but still monitor your systems to spot malicious activity early on.