How to prevent of path traversal in Asp.net core

Question

How to prevent of path traversal in my code below

Var filePath= Path.Combine(contentRootPath, fileName);

using (FileStream stream = System.IO.File.Create(filePath))
{
xxxxxxxxxxxx
xxxxxxxxxxxxx
xxxxxxxxxxxx
}

FileInfo file = new FileInfo(filePath);

if (file.Exists) and file.Delete() --> Path traversal attack

Please help to my code . If got let me know

Answer 1

Hi @Sumanth Babu

We can process the user's input filename. You can use filePath.Replace("..", "") before using the filePath to access the filesystem.

Var filePath= Path.Combine(contentRootPath, fileName);  
filePath = filePath.Replace("..", "");  

If you host your app in IIS, using either one of the RequestFilteringModule or UrlRoutingModule modules in IIS does effectively prevent my path traversal attack, provided the module(s) are fully-enabled.

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Jason

Answer 2

The answer is the same as your previous post, authorization.

Move the file outside of the wwwroot and use an action to fetch the file. The user must be authentication and authorized to invoke the HTTP action. There also the general design where the user is only able to access data related to the user's identity, role, or claim.