Use of Non-Canonical URL Paths for Authorization Decisions

Opis

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).

Skutki

• Access Control

  Bypass Protection Mechanism

  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).

Zapobieganie

• 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.

Słabość nadrzędna

• CWE-863 Incorrect Authorization
• CWE-180 Incorrect Behavior Order: Validate Before Canonicalize

Kiedy powstaje

• Implementation — REALIZATION: This weakness is caused during implementation of an architectural security tactic.
• Operation

Dotyczy

Not Language-Specific, Web Server