CWE-647: Use of Non-Canonical URL Paths for Authorization Decisions
Use of Non-Canonical URL Paths for Authorization Decisions
Weakness ID: 647 (Weakness Variant)
Status: Incomplete
Description
Description Summary
The software 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.
Extended Description
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).
Time of Introduction
Architecture and Design
Implementation
Operation
Applicable Platforms
Languages
All
Common Consequences
Scope
Effect
Access Control
Privilege Escalation
Confidentiality
Information Leakage
Likelihood of Exploit
High
Enabling Factors for Exploitation
An application specifies its policy namespaces and access control rules
based on the path information.
Alternate (but equivalent) encodings exist to represent the same path
information that will be understood and accepted by the process consuming
the path and granting access to resources.
Observed Examples
Reference
Description
Example from CAPEC (CAPEC ID: 4, "Using
Alternative IP Address Encodings") An attacker identifies an application
server that applies a security policy based on the domain and application
name, so the access control policy covers authentication and authorization
for anyone accessing http://example.domain:8080/application. However, by
putting in the IP address of the host the application authentication and
authorization controls may be bypassed http://192.168.0.1:8080/application.
The attacker relies on the victim applying policy to the namespace
abstraction and not having a default deny policy in place to manage
exceptions.
Potential Mitigations
Phase
Description
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.
Description
