CWE-647 — Use of Non-Canonical URL Paths for Authorization Decisions
CWE-647: Use of Non-Canonical URL Paths for Authorization Decisions
MITRE CWE weakness
| Kind | Weakness |
| Abstraction | Variant |
| Status | Incomplete |
| Likelihood of exploit | High |
Description
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.
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: Bypass Protection Mechanism
- Confidentiality: Read Files or Directories
Mitigations
Architecture and Design — 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.
Architecture and Design — Reject all alternate path encodings that are not in the expected canonical form.
References
- CWE page: https://cwe.mitre.org/data/definitions/647.html
- CWE list: https://cwe.mitre.org/data/index.html