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

Weakness Name

Use of Non-Canonical URL Paths for Authorization Decisions

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: 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

Scope:

Access Control

Impact:

Bypass Protection Mechanism

Notes:

An attacker may be able to bypass the authorization mechanism to gain access to the otherwise-protected URL.

Scope:

Confidentiality

Impact:

Read Files or Directories

Notes:

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).

Related Weaknesses

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