This is dangerous because an attacker can supply a value containing directory traversal sequences. If they send:
: Use Paths.get(input).normalize() and check if it starts with the allowed base directory.
: By repeating ..-2F multiple times, the attacker is attempting to "climb" out of the intended folder (the web root) and reach the base operating system folders.
Run your web application with the lowest possible privileges. The "web user" should never have permission to read the /root/ or /etc/ directories. -template-..-2F..-2F..-2F..-2Froot-2F
Use a database or an array map where an input of 1 loads default.html , and 2 loads profile.html .
: If the application decodes the input twice, an attacker might use %252f (where %25 decodes to % , resulting in %2f , which decodes again to / ).
Sample Encoded Path Value: item-template-..-2F..-2F..-2F..-2Froot-2F Notes: This string is used for testing URL decoding algorithms and filesystem boundary checks. This is dangerous because an attacker can supply
When decoded and normalized by a vulnerable backend server, the payload resolves to: -template-../../../../root/ Use code with caution.
Let's write. Understanding the Path Traversal Pattern: -template-..-2F..-2F..-2F..-2Froot-2F – A Deep Dive into Directory Traversal Attacks
Decoding the %2F sequences, which represent the forward slash / character in URL encoding: Run your web application with the lowest possible privileges
If the web server process runs with elevated privileges, it will read and display the contents of that restricted file to the attacker. Evasion Techniques: Why -2F Matters
However, if an attacker supplies the malicious keyword sequence: https://example.com
When a web developer builds a site that loads templates dynamically—such as changing a user's theme or interface layout via a parameter—they might write code that looks like this: