CVE-2025-59904: Kubysoft Stored XSS Vulnerability

CVE-2025-59904 Overview

CVE-2025-59904 is a Stored Cross-Site Scripting (XSS) vulnerability affecting Kubysoft, which is triggered through multiple parameters in the /kForms/app endpoint. This issue allows malicious scripts to be injected and executed persistently in the context of users accessing the affected resource.

Critical Impact

Attackers can inject persistent malicious JavaScript that executes in the browsers of all users who access the affected /kForms/app endpoint, potentially leading to session hijacking, credential theft, or further attack propagation.

Affected Products

• Kubysoft (specific versions not disclosed)

Discovery Timeline

• 2026-02-16 - CVE-2025-59904 published to NVD
• 2026-02-18 - Last updated in NVD database

Technical Details for CVE-2025-59904

Vulnerability Analysis

This vulnerability is classified as CWE-79 (Improper Neutralization of Input During Web Page Generation), commonly known as Cross-Site Scripting. The stored nature of this XSS vulnerability makes it particularly dangerous because the malicious payload persists on the server and affects all users who subsequently access the compromised resource.

The vulnerability exists within the /kForms/app endpoint of the Kubysoft application. Multiple parameters within this endpoint fail to properly sanitize user-supplied input before storing and rendering it back to users. When a victim accesses the affected resource, the stored malicious script executes within their browser session with full access to the page context, cookies, and session tokens.

Root Cause

The root cause of this vulnerability is the failure to implement proper input validation and output encoding on multiple parameters processed by the /kForms/app endpoint. User-supplied data is stored in the application database without adequate sanitization and is subsequently rendered in HTML responses without proper encoding, allowing JavaScript execution in the victim's browser context.

Attack Vector

The attack leverages the network-accessible /kForms/app endpoint and requires the attacker to have low-level privileges to submit the malicious payload. The attack also requires user interaction, as a victim must navigate to the page containing the stored malicious content for the XSS payload to execute.

An attacker would craft a malicious payload containing JavaScript code and submit it through one or more of the vulnerable parameters in the /kForms/app endpoint. Once stored, any user who accesses the affected resource will have the malicious script execute in their browser. This can be used to steal session cookies, perform actions on behalf of the victim, redirect users to phishing sites, or deface the application interface.

For detailed technical information about this vulnerability, refer to the INCIBE Advisory on Kubysoft Vulnerabilities.

Detection Methods for CVE-2025-59904

Indicators of Compromise

• Suspicious JavaScript payloads or encoded script tags in database fields associated with the /kForms/app endpoint
• Unusual form submissions containing <script> tags, event handlers (e.g., onerror, onload), or JavaScript URI schemes
• User reports of unexpected browser behavior or pop-ups when accessing Kubysoft forms
• Web application firewall logs showing blocked XSS attempts targeting the /kForms/app endpoint

Detection Strategies

• Implement web application firewall (WAF) rules to detect and block common XSS payloads in requests to the /kForms/app endpoint
• Enable Content Security Policy (CSP) headers to detect and prevent inline script execution, generating violation reports
• Conduct regular database audits to identify stored malicious content in fields related to form submissions
• Deploy endpoint detection solutions to monitor for suspicious JavaScript execution patterns in user browsers

Monitoring Recommendations

• Monitor web server access logs for high-frequency requests to /kForms/app with unusual parameter values
• Implement real-time alerting on CSP violation reports indicating potential XSS exploitation
• Review application logs for form submissions containing HTML entities or encoded script content
• Track user session anomalies that may indicate session hijacking following successful XSS exploitation

How to Mitigate CVE-2025-59904

Immediate Actions Required

• Apply vendor patches or updates for Kubysoft as soon as they become available
• Implement input validation to reject or sanitize HTML and JavaScript content in all /kForms/app parameters
• Enable Content Security Policy (CSP) headers to restrict inline script execution and mitigate XSS impact
• Review and sanitize existing database content for previously stored malicious payloads

Patch Information

Consult the INCIBE Advisory on Kubysoft Vulnerabilities for the latest patch information and vendor guidance. Contact the Kubysoft vendor directly for specific patch availability and installation instructions.

Workarounds

• Implement server-side input validation to strip or encode HTML special characters (<, >, ", ', &) from all user-supplied parameters
• Deploy a Web Application Firewall (WAF) with XSS protection rules in front of the Kubysoft application
• Restrict access to the /kForms/app endpoint to trusted users or IP ranges until a patch is available
• Enable HTTP-only and Secure flags on session cookies to limit the impact of potential session hijacking via XSS

# Example Content Security Policy configuration for Apache
# Add to .htaccess or virtual host configuration
Header set Content-Security-Policy "default-src 'self'; script-src 'self'; object-src 'none'; style-src 'self' 'unsafe-inline';"
Header set X-XSS-Protection "1; mode=block"
Header set X-Content-Type-Options "nosniff"