Lack of data validation - Path Traversal
Need
Prevent unauthorized access to files and directories outside the intended path scope.
Context
- Usage of Elixir for building scalable and fault-tolerant applications
- Usage of Plug and Cowboy for HTTP request and response handling
- File access or operations based on user-supplied path
Description
Non compliant code
defmodule VulnerableApp do
use Plug.Router
plug :match
plug :dispatch
get '/read_file' do
path = conn.params['path']
file_content = File.read!(path)
send_resp(conn, 200, file_content)
end
end
This code takes a user-supplied path to read a file without validating or sanitizing the input, allowing an attacker to access files outside the intended directory.
Steps
- Always validate and sanitize user-supplied input.
- Prevent the user from supplying the full path; consider using identifiers to reference files or directories.
- Use a whitelist of allowed paths or files.
- Check for path traversal sequences (.., ~, /) in the user input and neutralize them.
Compliant code
defmodule SecureApp do
use Plug.Router
plug :match
plug :dispatch
get '/read_file' do
path = conn.params['path']
if valid_path?(path) do
file_content = File.read!(path)
send_resp(conn, 200, file_content)
else
send_resp(conn, 400, 'Bad Request')
end
end
defp valid_path?(path) do
# Add your path validation logic here
end
end
This code validates and sanitizes the user-supplied path before reading the file, effectively preventing path traversal attacks.