CVE-2025-5591: Kentico Xperience 13 XSS Vulnerability

CVE-2025-5591 Overview

CVE-2025-5591 is a stored cross-site scripting (XSS) vulnerability affecting Kentico Xperience 13. The vulnerability exists within a form component, allowing attackers to inject and persist malicious scripts that execute in the context of victim users' browsers. When successfully exploited, attackers can hijack user sessions and perform unauthorized actions within the victim's security context.

Critical Impact

Successful exploitation enables session hijacking and allows attackers to perform actions as the compromised user, potentially leading to account takeover and data theft.

Affected Products

• Kentico Xperience 13

Discovery Timeline

• 2026-01-05 - CVE-2025-5591 published to NVD
• 2026-01-08 - Last updated in NVD database

Technical Details for CVE-2025-5591

Vulnerability Analysis

This stored cross-site scripting vulnerability (CWE-79) allows attackers to inject malicious JavaScript code through a form component in Kentico Xperience 13. Unlike reflected XSS attacks that require user interaction with a malicious link, stored XSS persists the malicious payload within the application, making it more dangerous as the attack executes automatically when victims view the affected content.

The vulnerability enables attackers to execute arbitrary JavaScript in the victim's browser session. This can be leveraged for session hijacking, credential theft, keylogging, defacement, or redirecting users to malicious sites. Given the nature of content management systems like Kentico Xperience, administrative users are particularly high-value targets as compromising their sessions could grant attackers full control over the application.

Root Cause

The vulnerability stems from insufficient input sanitization and output encoding in the form component functionality. User-supplied input is stored and subsequently rendered without proper validation or escaping, allowing HTML and JavaScript code to be interpreted by the browser rather than displayed as text.

Attack Vector

The attack is network-based and requires no privileges to execute, though user interaction is necessary—the victim must view the page containing the stored malicious payload. An attacker would typically:

1. Identify a vulnerable form field in Kentico Xperience 13
2. Submit a form containing malicious JavaScript payload
3. The payload is stored in the application's database
4. When an authenticated user (especially administrators) views the stored content, the malicious script executes in their browser
5. The attacker can then capture session tokens, perform actions as the victim, or exfiltrate sensitive data

The attack requires no authentication from the attacker's perspective, making it accessible to anonymous users who can submit forms on the target application.

Detection Methods for CVE-2025-5591

Indicators of Compromise

• Unusual JavaScript patterns in stored form submissions, particularly <script> tags or event handlers like onerror, onload, onclick
• Form field values containing encoded JavaScript such as URL-encoded or HTML-encoded script patterns
• Unexpected outbound network connections from client browsers to unfamiliar domains
• Session anomalies indicating potential session hijacking, such as session usage from multiple geographic locations

Detection Strategies

• Implement Web Application Firewall (WAF) rules to detect and block XSS payloads in form submissions
• Enable content security policy (CSP) reporting to identify and log inline script execution attempts
• Review application logs for form submissions containing suspicious HTML or JavaScript content
• Deploy browser-based XSS auditing tools and monitoring for client-side security events

Monitoring Recommendations

• Monitor form submission logs for patterns consistent with XSS payloads including script tags, event handlers, and JavaScript URIs
• Configure alerting on CSP violation reports to detect attempted script injection
• Implement real-time monitoring of administrator account activity for signs of session compromise
• Review stored content periodically for unexpected or malicious code injection

How to Mitigate CVE-2025-5591

Immediate Actions Required

• Review and audit all form components in Kentico Xperience 13 for stored XSS vulnerabilities
• Implement strict input validation and output encoding for all user-supplied content
• Deploy Content Security Policy (CSP) headers to restrict inline script execution
• Consider temporarily disabling or restricting access to vulnerable form components until patched

Patch Information

Refer to the The Missing Link Security Advisory for detailed patch information and vendor guidance. Organizations should monitor Kentico's official security channels for updates and apply patches as they become available.

Workarounds

• Implement server-side input validation that strips or encodes HTML and JavaScript from form submissions
• Deploy a Web Application Firewall with XSS protection rules to filter malicious payloads
• Implement strict Content Security Policy headers to prevent execution of injected scripts
• Restrict form submission capabilities to authenticated users only where business requirements allow

# Example Content Security Policy header configuration
# Add to web server configuration or application response headers
Content-Security-Policy: default-src 'self'; script-src 'self'; object-src 'none'; style-src 'self' 'unsafe-inline'; frame-ancestors 'self';