CWE-647 Variant Incomplete High likelihood

Use of Non-Canonical URL Paths for Authorization Decisions

This vulnerability occurs when an application's authorization logic relies on specific URL paths but fails to enforce a single, standardized format. Attackers can bypass access controls by using…

Definition

What is CWE-647?

This vulnerability occurs when an application's authorization logic relies on specific URL paths but fails to enforce a single, standardized format. Attackers can bypass access controls by using alternative, equivalent URL formats that the system doesn't recognize as the same protected resource.
Applications often define access rules for specific URLs, but many different URL formats can point to the same page. If the authorization check doesn't first convert URLs to a canonical (standardized) form, attackers can use variations like different character encodings, case changes, IP addresses instead of domain names, trailing slashes, or explicit port numbers to bypass security checks. Each variation appears different to the authorization system while loading the same protected content. To prevent this, always normalize URLs to a single canonical format before checking permissions. Implement a default-deny approach that rejects any non-standard URL format. This involves stripping unnecessary elements like default ports, removing trailing slashes, converting to lowercase, decoding encoded characters, and resolving hostnames consistently before any authorization decision is made.
Real-world impact

Real-world CVEs caused by CWE-647

No public CVE references are linked to this CWE in MITRE's catalog yet.

How attackers exploit it

Step-by-step attacker path

  1. 1

    Identify a code path that handles untrusted input without validation.

  2. 2

    Craft a payload that exercises the unsafe behavior — injection, traversal, overflow, or logic abuse.

  3. 3

    Deliver the payload through a normal request and observe the application's reaction.

  4. 4

    Iterate until the response leaks data, executes attacker code, or escalates privileges.

Vulnerable code example

Vulnerable pseudo

MITRE has not published a code example for this CWE. The pattern below is illustrative — see Resources for canonical references.

Vulnerable pseudo 
// Example pattern — see MITRE for the canonical references.
function handleRequest(input) {
  // Untrusted input flows directly into the sensitive sink.
  return executeUnsafe(input);
}
Secure code example

Secure pseudo

Secure pseudo 
// Validate, sanitize, or use a safe API before reaching the sink.
function handleRequest(input) {
  const safe = validateAndEscape(input);
  return executeWithGuards(safe);
}
What changed: the unsafe sink is replaced (or the input is validated/escaped) so the same payload no longer triggers the weakness.
Prevention checklist

How to prevent CWE-647

  • 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.
Detection signals

How to detect CWE-647

Automated Static Analysis High

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.)

Plexicus auto-fix

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Frequently asked questions

Frequently asked questions

What is CWE-647?

This vulnerability occurs when an application's authorization logic relies on specific URL paths but fails to enforce a single, standardized format. Attackers can bypass access controls by using alternative, equivalent URL formats that the system doesn't recognize as the same protected resource.

How serious is CWE-647?

MITRE rates the likelihood of exploit as High — this weakness is actively exploited in the wild and should be prioritized for remediation.

What languages or platforms are affected by CWE-647?

MITRE lists the following affected platforms: Web Server.

How can I prevent CWE-647?

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.

How does Plexicus detect and fix CWE-647?

Plexicus's SAST engine matches the data-flow signature for CWE-647 on every commit. When a match is found, our Codex Remedium agent opens a fix PR with the corrected code, tests, and a one-line summary for the reviewer.

Where can I learn more about CWE-647?

MITRE publishes the canonical definition at https://cwe.mitre.org/data/definitions/647.html. You can also reference OWASP and NIST documentation for adjacent guidance.

Related weaknesses

Weaknesses related to CWE-647

CWE-863 Parent

Incorrect Authorization

This vulnerability occurs when an application checks if a user is allowed to perform an action or access data, but the check is flawed or…

CWE-1244 Sibling

Internal Asset Exposed to Unsafe Debug Access Level or State

This vulnerability occurs when a system's debug or test interface supports multiple access levels, but an internal asset is incorrectly…

CWE-551 Sibling

Incorrect Behavior Order: Authorization Before Parsing and Canonicalization

This vulnerability occurs when a web server checks access permissions before fully processing and normalizing a URL, potentially allowing…

CWE-639 Sibling

Authorization Bypass Through User-Controlled Key

This vulnerability occurs when an application's authorization system fails to verify that a user is allowed to access specific data before…

CWE-804 Sibling

Guessable CAPTCHA

This vulnerability occurs when a CAPTCHA challenge is too easy for automated bots to solve, either by guessing or using pattern…

CWE-942 Sibling

Permissive Cross-domain Security Policy with Untrusted Domains

This vulnerability occurs when a web application's cross-domain security policy, like a Content Security Policy (CSP), explicitly allows…

Resources

Further reading

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