CWE

Use of Non-Canonical URL Paths for Authorization Decisions

ID: 647		Date: (C)2012-05-14   (M)2022-10-10
Type: weakness		Status: INCOMPLETE
Abstraction Type: Variant

Description

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:

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).

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.

Likelihood of Exploit: High

Applicable Platforms
Language Class: Language-independent
Architectural Paradigm: Web-based

Time Of Introduction

• Architecture and Design
• Implementation
• Operation

Common Consequences

Scope	Technical Impact	Notes
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).

Detection Methods
None

Potential Mitigations

Phase	Strategy	Description	Effectiveness	Notes
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.

Relationships

Related CWE	Type	View	Chain
CWE-647 ChildOf CWE-898	Category	CWE-888

Demonstrative Examples
None

Observed Examples

1. : 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.

For more examples, refer to CVE relations in the bottom box.

White Box Definitions
None

Black Box Definitions
None

Taxynomy Mappings

Taxynomy	Id	Name	Fit
CERT Java Secure Coding	IDS02-J	Canonicalize path names before validating them

References:
None