Course

The Code Review Snippet challenges are designed to help you identify vulnerabilities within small code snippets. In this particular challenge, we analyze the myflaskapp.py script, which sets up a simple HTTP server. The script is vulnerable to directory traversal attacks due to an inadequate regular expression filter on line nine. This filter attempts to block paths containing "../..", but it can be easily bypassed with paths like ".././../". The objective is to understand how such vulnerabilities arise and how they can be mitigated.

First, the script imports necessary modules and defines a MyServer class that inherits from BaseHTTPRequestHandler. The do_GET method processes incoming GET requests by concatenating the current working directory with the requested path. If the path ends with a slash, it appends "index.html". The filter on line nine is supposed to prevent directory traversal but fails due to an overly simplistic pattern. Consequently, an attacker can access sensitive files outside the intended directory by crafting specific path strings. This challenge showcases the importance of robust input validation and the potential risks of inadequate filtering.