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

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).

Source-backed guidance

Additional facts reviewed against primary or authoritative security sources.

Verify controls for CWE-647 with SSDF evidence

Use NIST SSDF verification and vulnerability-response practices to detect CWE-647, Use of Non-Canonical URL Paths for Authorization Decisions, throughout the product lifecycle. Derive review questions, static or dynamic checks, and negative tests from the CWE's causal behavior; define the components and lifecycle stages each check covers; and retain findings with enough evidence to distinguish the root cause from symptoms and impacts. Track escapes and false negatives, then improve the verification plan after every confirmed occurrence.

NIST SP 800-218 Secure Software Development Framework — National Institute of Standards and Technology

Address Use of Non-Canonical URL Paths for Authorization Decisions during Architecture and Design

MITRE associates mitigation with Architecture and Design; documented detection approaches include Automated Static Analysis; recorded impacts include Bypass Protection Mechanism, and Read Files or Directories. Use these source-defined anchors to turn CWE-647 into implementation, review, and verification checks for the affected component.

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

Triage CWE-647 against known exploitation evidence

Use CISA's Known Exploited Vulnerabilities catalog to test whether a vulnerability mapped to CWE-647, Use of Non-Canonical URL Paths for Authorization Decisions, has evidence of exploitation in the wild. Confirm the CVE-to-CWE root-cause mapping independently before attaching the example, then capture the affected product, required action, and remediation deadline. A missing KEV match is not evidence that the weakness is unexploited, and a KEV entry must not be generalized to every occurrence of this CWE.

Known Exploited Vulnerabilities Catalog — Cybersecurity and Infrastructure Security Agency

Apply precise root-cause mapping to CWE-647

Apply MITRE's full root-cause mapping guidance when using CWE-647, Use of Non-Canonical URL Paths for Authorization Decisions. Separate weakness language from attacker prerequisites and technical impact, check the entry's abstraction and vulnerability-mapping notes, and prefer the most specific Base or Variant supported by the evidence. Record the rejected alternatives and require an independent review before the mapping is used for remediation trends or program metrics.

CVE to CWE Root Cause Mapping Guidance — MITRE CWE

Validate CWE-647 with root-cause mapping checks

Apply MITRE's root-cause mapping quick tips to CWE-647, Use of Non-Canonical URL Paths for Authorization Decisions. Confirm the finding describes the causal weakness rather than an impact or attack pattern, compare the abstraction and mapping notes with plausible alternatives, and have a second reviewer challenge the selection. Preserve the evidence and reasoning so recurring defects can be measured against one consistent identifier.

CVE to CWE Root Cause Mapping Quick Tips — MITRE 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.

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

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