GHSA-8v2v-wjwg-vx6r: 
Rust vulnerability analysis and mitigation

Summary

When passing a non-existing folder to the actix_files::Files::new() method causes the actix server to expose unexpected files.

Details

The actix-files library exposes a Files struct that configures an actix service to serve the files in a folder as static assets. Below you can find the signature of the Files::new method:

pub fn new<T: Into<PathBuf>>(mount_path: &str, serve_from: T) -> Files

When the mount_path you pass to Files doesn't exist, it defaults to an empty path (Path::new()). When the service receives a HTTP request, it joins the request information with the empty path and calls canonicalize. Rust resolves this path as relative and returns any file that matches it. This behavior causes the library to expose unexpected files when the folder is not present.

PoC

There is a working PoC on https://github.com/Angelmmiguel/actix-files-vuln, although the next steps can be followed to reproduce the issue

1. Clone the https://github.com/actix/examples repository.

2. Change your directory to the basics/static-files folder.

3. Edit the src/main.rs file and change the line 13 to mount a non-existing folder:

   -        .service(Files::new("/images", "static/images/").show_files_listing())
   +        .service(Files::new("/images", "static/missing/").show_files_listing())

4. Run the project with cargo run.

5. Access the http://localhost:8080/images/Cargo.toml URL.

Impact

This is an exposure of information vulnerability. It affects anyone using the actix-files::Files library that mounts a non-existing folder for any reason.