CWE-647

Use of Non-Canonical URL Paths for Authorization Decisions
AI Translation Available

The product defines policy namespaces and makes authorization decisions based on the assumption that a URL is canonical. This can allow a non-canonical URL to bypass the authorization.

Status
incomplete
Abstraction
variant
Likelihood
high
Web Server

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

Therefore it is important to specify access control policy that is based on the path information in some canonical form with all alternate encodings rejected (which can be accomplished by a default deny rule).

Common Consequences

access control confidentiality
Impacts
bypass protection mechanism read files or directories

Detection Methods

automated static analysis

Potential Mitigations

Phases:
architecture and design
Descriptions:
• Reject all alternate path encodings that are not in the expected canonical form.
• Make access control policy based on path information in canonical form. Use very restrictive regular expressions to validate that the path is in the expected form.