How to remediate – Yuzo Related Posts Plugin for WordPress Cross-Site Scripting

1. Introduction

The Yuzo Related Posts Plugin for WordPress Cross-Site Scripting (XSS) vulnerability allows an attacker to inject malicious scripts into web pages viewed by other users. This can lead to the theft of cookies, redirection to harmful websites, or defacement of the website. Systems running vulnerable versions of the Yuzo Related Posts plugin are affected. A successful exploit could compromise confidentiality, integrity and availability of a WordPress site.

2. Technical Explanation

The vulnerability is caused by improper sanitization of user-supplied input within the Yuzo Related Posts Plugin for WordPress. An attacker can inject arbitrary JavaScript code through unsanitized parameters which will then be executed in the context of other users’ browsers when they view affected pages. The scanner relied on self-reported version numbers and has not tested exploitation directly. CVE-2019-11869 describes this issue.

• Root cause: Insufficient input validation allows arbitrary JavaScript to be injected into the WordPress site.
• Exploit mechanism: An attacker crafts a malicious URL containing XSS payload, which is then executed when another user visits that URL. For example, an attacker could inject a script tag with a redirect to a phishing website.
• Scope: WordPress websites using Yuzo Related Posts Plugin versions prior to the fix are affected.

3. Detection and Assessment

Confirming vulnerability involves checking the installed plugin version. A thorough assessment requires reviewing source code for input sanitization.

• Quick checks: In the WordPress admin interface, navigate to Plugins > Installed Plugins and check the Yuzo Related Posts Plugin version.
• Scanning: Wordfence scanners may detect this vulnerability using signature ID 1234567 (example only).
• Logs and evidence: Examine web server access logs for unusual requests containing JavaScript code or encoded characters in URL parameters.

wp plugin list | grep yuzo-related-post

4. Solution / Remediation Steps

The recommended solution is to remove the vulnerable plugin.

4.1 Preparation

• No services need to be stopped, but it’s good practice to take the site into maintenance mode during updates. A roll back plan is to restore from backup.
• Change windows are not typically needed for plugin removal, but approval may be required by some organisations.

4.2 Implementation

1. Step 1: Deactivate the Yuzo Related Posts Plugin through the WordPress admin interface (Plugins > Installed Plugins).
2. Step 2: Delete the Yuzo Related Posts Plugin through the WordPress admin interface (Plugins > Installed Plugins).

4.3 Config or Code Example

No config or code changes are needed; this fix involves removing the plugin.

4.4 Security Practices Relevant to This Vulnerability

Several security practices can help prevent XSS vulnerabilities. Least privilege limits damage from exploitation, while input validation blocks unsafe data.

• Practice 1: Implement least privilege for WordPress users and plugins to reduce the impact of a successful attack.
• Practice 2: Enforce strict input validation on all user-supplied data to prevent malicious code injection.

4.5 Automation (Optional)

Automated removal is possible via WP-CLI, but requires caution.

wp plugin deactivate yuzo-related-post --all && wp plugin uninstall yuzo-related-post --all

5. Verification / Validation

Confirm the fix by verifying that the plugin is no longer installed and retesting for XSS vulnerabilities.

• Post-fix check: Run `wp plugin list` and confirm that Yuzo Related Posts Plugin does not appear in the output.
• Re-test: Attempt to inject a simple XSS payload into a URL parameter where the plugin was previously used. Verify that the payload is not executed.
• Monitoring: Monitor web server logs for any attempts to access resources related to the removed plugin (example only).

wp plugin list | grep yuzo-related-post # should return no output

6. Preventive Measures and Monitoring

Regular security baselines and patch management are important for preventing vulnerabilities like this one. Consider using SAST tools to identify input validation issues.

• Baselines: Update your WordPress security baseline to include a list of approved plugins and regularly review plugin installations.
• Pipelines: Integrate Static Application Security Testing (SAST) into your CI/CD pipeline to scan for XSS vulnerabilities in WordPress themes and plugins.
• Asset and patch process: Implement a regular patch management cycle for WordPress core, themes, and plugins.

7. Risks, Side Effects, and Roll Back

Removing the plugin may break functionality that relies on it. Restore from backup to roll back.

• Risk or side effect 1: Removing the plugin may cause related posts sections to disappear from your website.
• Risk or side effect 2: If other plugins depend on Yuzo Related Posts, they may also be affected.

8. References and Resources

Official advisories and documentation are key resources for this vulnerability.

• Vendor advisory or bulletin: https://wordpress.org/plugins/yuzo-related-post/
• NVD or CVE entry: CVE-2019-11869
• Product or platform documentation relevant to the fix: N/A