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:

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).

+ Time of Introduction
  • Architecture and Design
  • Implementation
  • Operation
+ Applicable Platforms

Languages

All

+ Common Consequences
ScopeEffect
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
ReferenceDescription
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: 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.

Phase: Architecture and Design

Reject all alternate path encodings that are not in the expected canonical form.

+ Relationships
NatureTypeIDNameView(s) this relationship pertains toView(s)
ChildOfWeakness ClassWeakness Class284Access Control (Authorization) Issues
Development Concepts (primary)699
Research Concepts (primary)1000
ChildOfCategoryCategory442Web Problems
Development Concepts699
+ Content History
Submissions
Submission DateSubmitterOrganizationSource
2008-01-30Evgeny LebanidzeCigitalExternal Submission
Modifications
Modification DateModifierOrganizationSource
2008-09-08CWE Content TeamMITREInternal
updated Common Consequences, Relationships
2008-10-14CWE Content TeamMITREInternal
updated Description, Name, Potential Mitigations, Relationships
2009-10-29CWE Content TeamMITREInternal
updated Common Consequences
Previous Entry Names
Change DatePrevious Entry Name
2008-10-14Using Non-Canonical Paths for Authorization Decisions
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