CWE-647 Use of Non-Canonical URL Paths for Authorization Decisions

The product defines policy namespaces and makes authorization decisions based on the assumption that a URL is canonical.

If an application defines policy namespaces and makes authorization decisions based on the URL, but it does not require or convert to a canonical URL before making the authorization decision, then it opens the application to attack. For example, if the application only wants to allow access to http://www.example.com/mypage, then the attacker might be able to bypass this restriction using equivalent URLs such as: • http://WWW.EXAMPLE.COM/mypage • http://www.example.com/%6Dypage (alternate encoding) • http://192.168.1.1/mypage (IP address) • http://www.example.com/mypage/ (trailing /) • http://www.example.com:80/mypage

• Access Control: Bypass Protection Mechanism — This can allow a non-canonical URL to bypass the authorization. An attacker may be able to bypass the authorization mechanism to gain access to the otherwise-protected URL. • Confidentiality: Read Files or Directories — If a non-canonical URL is used, the server may choose to return the contents of the file, instead of pre-processing the file (e.g. as a program).

• [Architecture and Design] Make access control policy based on path information in canonical form, with all alternate encodings rejected (which can be accomplished by a default deny rule). Consider very restrictive regular expressions to validate that the path is in the expected form. Reject all alternate path encodings that are not in the expected canonical form.

• Automated Static Analysis: Automated static analysis, commonly referred to as Static Application Security Testing (SAST), can find some instances of this weakness by analyzing source code (or binary/compiled code) without having to execute it. Typically, this is done by building a model of data flow and control flow, then searching for potentially-vulnerable patterns that connect "sources" (origins of input) with "sinks" (destinations where the data interacts with external components, a lower layer such as the OS, etc.)