Fix: Prevent registration bypass when user registration is disabled

[jonathancaron]

Fix: Prevent registration bypass when user registration is disabled

Problem Description:

After extensive testing, I discovered a potential vulnerability in the default WordPress registration form. This issue occurs even when user registration is disabled (users_can_register set to 0). It allows spammers to bypass the restriction and create accounts, resulting in spam registrations and automated email notifications.

Steps to Reproduce:

1. Send a POST request to /wp-login.php?action=register.
2. Headers:
• Content-Type: application/x-www-form-urlencoded
3. Body (as x-www-form-urlencoded):

user_login=testuser
user_email=testuser@example.com
user_pass=TestPassword123
wp-submit=Register
redirect_to=
    

4. Response:

If the same request is repeated, an error is displayed indicating that the username and email are already in use.

5. Redirect Behavior:

The bypass works only when redirect following is disabled.

Root Cause:

The wp-login.php file does not validate whether the users_can_register option is disabled when processing registration requests.

Solution:

This pull request introduces a check to block access to the registration process if the users_can_register option is set to 0. This ensures that no new accounts can be created through this endpoint unless registration is explicitly enabled.

Trac ticket: https://core.trac.wordpress.org/ticket/62905

[github-actions]

The following accounts have interacted with this PR and/or linked issues. I will continue to update these lists as activity occurs. You can also manually ask me to refresh this list by adding the props-bot label.

Core Committers: Use this line as a base for the props when committing in SVN:

Props jonathancaron02.

To understand the WordPress project's expectations around crediting contributors, please review the Contributor Attribution page in the Core Handbook.

[github-actions]

Hi @jonathancaron! 👋

Thank you for your contribution to WordPress! 💖

It looks like this is your first pull request to wordpress-develop. Here are a few things to be aware of that may help you out!

No one monitors this repository for new pull requests. Pull requests must be attached to a Trac ticket to be considered for inclusion in WordPress Core. To attach a pull request to a Trac ticket, please include the ticket's full URL in your pull request description.

Pull requests are never merged on GitHub. The WordPress codebase continues to be managed through the SVN repository that this GitHub repository mirrors. Please feel free to open pull requests to work on any contribution you are making.

More information about how GitHub pull requests can be used to contribute to WordPress can be found in the Core Handbook.

Please include automated tests. Including tests in your pull request is one way to help your patch be considered faster. To learn about WordPress' test suites, visit the Automated Testing page in the handbook.

If you have not had a chance, please review the Contribute with Code page in the WordPress Core Handbook.

The Developer Hub also documents the various coding standards that are followed:

• PHP Coding Standards
• CSS Coding Standards
• HTML Coding Standards
• JavaScript Coding Standards
• Accessibility Coding Standards
• Inline Documentation Standards

Thank you,
The WordPress Project

[jonathancaron]

Trac ticket added.

[github-actions]

Test using WordPress Playground

The changes in this pull request can previewed and tested using a WordPress Playground instance.

WordPress Playground is an experimental project that creates a full WordPress instance entirely within the browser.

Some things to be aware of

• The Plugin and Theme Directories cannot be accessed within Playground.
• All changes will be lost when closing a tab with a Playground instance.
• All changes will be lost when refreshing the page.
• A fresh instance is created each time the link below is clicked.
• Every time this pull request is updated, a new ZIP file containing all changes is created. If changes are not reflected in the Playground instance,
  it's possible that the most recent build failed, or has not completed. Check the list of workflow runs to be sure.

For more details about these limitations and more, check out the Limitations page in the WordPress Playground documentation.

Test this pull request with WordPress Playground.