CWE-647: Use of Non-Canonical URL Paths for Authorization Decisions
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.
View on MITREExtended 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).
Technical Details
- Structure
- Simple
Applicable To
Security Consequences
Scope
Impact
An attacker may be able to bypass the authorization mechanism to gain access to the otherwise-protected URL.
Scope
Impact
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).
Mitigation Strategies
Phase
Description
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
Description
Reject all alternate path encodings that are not in the expected canonical form.
Detection Methods
No detection method information available for this CWE.
Code Examples & CVEs
No examples or observed CVEs available for this CWE.
CWE Relationships
No relationship information available for this CWE.
Frequently Asked Questions
What is CWE-647: Use of Non-Canonical URL Paths for Authorization Decisions?+
CWE-647: Use of Non-Canonical URL Paths for Authorization Decisions is a Common Weakness Enumeration (CWE) entry maintained by MITRE. 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).
What are the security consequences of Use of Non-Canonical URL Paths for Authorization Decisions?+
If exploited, CWE-647 (Use of Non-Canonical URL Paths for Authorization Decisions) it can compromise Access Control and Confidentiality, leading to outcomes such as Bypass Protection Mechanism and Read Files or Directories.
How do you prevent or mitigate Use of Non-Canonical URL Paths for Authorization Decisions?+
Recommended mitigations for CWE-647 include: 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. Reject all alternate path encodings that are not in the expected canonical form.
Which programming languages are affected by Use of Non-Canonical URL Paths for Authorization Decisions?+
CWE-647 commonly affects Not Language-Specific. Note that weaknesses are often language-agnostic patterns, so secure coding practices apply broadly.
What is the difference between a CWE and a CVE?+
A CWE (Common Weakness Enumeration) like CWE-647 describes a category of software weakness — the underlying flaw type. A CVE (Common Vulnerabilities and Exposures) identifies a specific, real-world vulnerability in a particular product. In short, a CWE is the kind of mistake, and a CVE is an instance of that mistake being found in software.