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:

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).

Primary

Implementation
REALIZATION: This weakness is caused during implementation of an architectural security tactic.

Operation

High

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).

Automated Static Analysis
Automated static analysis, commonly referred to as Static Application Security Testing (SAST), can find some instances of this weakness by analyzing source code (or binary/compiled code) without having to execute it. Typically, this is done by building a model of data flow and control flow, then searching for potentially-vulnerable patterns that connect "sources" (origins of input) with "sinks" (destinations where the data interacts with external components, a lower layer such as the OS, etc.)
High

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.

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.

IDS02-J
Canonicalize path names before validating them

Allowed
This CWE entry is at the Variant level of abstraction, which is a preferred level of abstraction for mapping to the root causes of vulnerabilities.
Carefully read both the name and description to ensure that this mapping is an appropriate fit. Do not try to 'force' a mapping to a lower-level Base/Variant simply to comply with this preferred level of abstraction.

Evgeny Lebanidze
Cigital
2008-01-30
Draft 8
2008-01-30

CWE Content Team
MITRE
2008-09-08
updated Common_Consequences, Relationships

CWE Content Team
MITRE
2008-10-14
updated Description, Name, Potential_Mitigations, Relationships

CWE Content Team
MITRE
2009-10-29
updated Common_Consequences

CWE Content Team
MITRE
2010-12-13
updated Common_Consequences

CWE Content Team
MITRE
2011-03-29
updated Relationships

CWE Content Team
MITRE
2011-06-01
updated Applicable_Platforms, Common_Consequences, Relationships, Taxonomy_Mappings

CWE Content Team
MITRE
2012-05-11
updated Relationships, Taxonomy_Mappings

CWE Content Team
MITRE
2014-07-30
updated Relationships

CWE Content Team
MITRE
2017-11-08
updated Demonstrative_Examples, Enabling_Factors_for_Exploitation, Modes_of_Introduction, Observed_Examples, Relationships

CWE Content Team
MITRE
2019-01-03
updated Relationships, Taxonomy_Mappings

CWE Content Team
MITRE
2020-02-24
updated Applicable_Platforms, Relationships

CWE Content Team
MITRE
2023-01-31
updated Description

CWE Content Team
MITRE
2023-04-27
updated Detection_Factors, Relationships, Time_of_Introduction

CWE Content Team
MITRE
2023-06-29
updated Mapping_Notes

CWE Content Team
MITRE
2025-12-11
4.19
2025-12-11
updated Relationships, Weakness_Ordinalities

Using Non-Canonical Paths for Authorization Decisions