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

Weakness ID: 647
Abstraction: Variant
Status: Incomplete
Presentation Filter:
+ 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, then the attacker might be able to bypass this restriction using equivalent URLs such as:

  • http://WWW.EXAMPLE.COM/mypage

  • (alternate encoding)

  • (IP address)

  • (trailing /)


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



Architectural Paradigms


+ Common Consequences
Access Control

Technical Impact: Bypass protection mechanism

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


Technical Impact: 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).

+ Likelihood of Exploit


+ 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
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 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)
ChildOfCategoryCategory442Web Problems
Development Concepts699
ChildOfCategoryCategory845CERT Java Secure Coding Section 00 - Input Validation and Data Sanitization (IDS)
Weaknesses Addressed by the CERT Java Secure Coding Standard (primary)844
ChildOfWeakness ClassWeakness Class863Incorrect Authorization
Development Concepts (primary)699
Research Concepts (primary)1000
ChildOfCategoryCategory949SFP Secondary Cluster: Faulty Endpoint Authentication
Software Fault Pattern (SFP) Clusters (primary)888
+ Taxonomy Mappings
Mapped Taxonomy NameNode IDFitMapped Node Name
CERT Java Secure CodingIDS02-JCanonicalize path names before validating them
+ Content History
Submission DateSubmitterOrganizationSource
2008-01-30Evgeny LebanidzeCigitalExternal Submission
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
2010-12-13CWE Content TeamMITREInternal
updated Common_Consequences
2011-03-29CWE Content TeamMITREInternal
updated Relationships
2011-06-01CWE Content TeamMITREInternal
updated Applicable_Platforms, Common_Consequences, Relationships, Taxonomy_Mappings
2012-05-11CWE Content TeamMITREInternal
updated Relationships, Taxonomy_Mappings
2014-07-30CWE Content TeamMITREInternal
updated Relationships
Previous Entry Names
Change DatePrevious Entry Name
2008-10-14Using Non-Canonical Paths for Authorization Decisions

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Page Last Updated: May 05, 2017