Need

Prevent unauthorized access to temporary files

Context

• Usage of Elixir (v1.10+) for building scalable and fault-tolerant applications
• Usage of Plug for request handling
• Usage of Phoenix framework for building web applications

Description

Non compliant code

        File.mkdir("/tmp/my_temp_dir")
File.write!({"/tmp/my_temp_dir", "my_temp_file"}, "sensitive data")
        
        

This code is vulnerable because it creates a temporary file in the default '/tmp' directory and writes sensitive data into it. Any other user on the same system can read the file and potentially misuse the data.

Steps

• Use a safer alternative like `Path.join(System.tmp_dir(), "my_temp_dir")` to get a path to a temporary directory which respects the operating system’s conventions.
• Make sure the directory is only readable and writable by the owner with a permission mask of 0600.

Compliant code

        File.mkdir_p!({:ok, path} = File.mktemp(System.tmp_dir(), "my_temp_dir"))
File.chmod!(path, 0o600)
File.write!({path, "my_temp_file"}, "sensitive data")
        
        

This secure code example creates a temporary directory in a way that respects the operating system’s conventions. It then sets the file permissions to 0600, making the file only readable and writable by the owner. Finally, it writes the sensitive data to the file.

References

• 160. Excessive privileges - Temporary Files