CVE-2025-10503: Authentication Endpoint XSS Vulnerability

CVE-2025-10503 Overview

CVE-2025-10503 is a reflected Cross-Site Scripting (XSS) vulnerability affecting WSO2 products. The authentication endpoint accepts user-supplied input without enforcing expected validation constraints, leading to a lack of proper output encoding. This allows for the injection of malicious JavaScript payloads, enabling reflected cross-site scripting attacks.

An attacker can leverage this vulnerability to redirect the user's browser to a malicious website, modify the user interface of the web page, retrieve information from the browser, or cause other harmful actions. However, due to the protection of session-related cookies with the httpOnly flag, session hijacking is not possible.

Critical Impact

Attackers can inject malicious JavaScript through the authentication endpoint, potentially redirecting users to phishing sites, defacing web interfaces, or stealing sensitive browser-accessible data.

Affected Products

• WSO2 Products (specific versions listed in security advisory WSO2-2025-4577)

Discovery Timeline

• 2026-04-29 - CVE CVE-2025-10503 published to NVD
• 2026-04-29 - Last updated in NVD database

Technical Details for CVE-2025-10503

Vulnerability Analysis

This vulnerability is classified as CWE-79 (Improper Neutralization of Input During Web Page Generation), commonly known as Cross-Site Scripting. The flaw exists in the authentication endpoint where user-supplied input is reflected back to the user without proper validation or output encoding.

When a user submits data to the authentication endpoint, the application fails to sanitize special characters that have meaning in HTML and JavaScript contexts. This allows an attacker to craft malicious URLs containing JavaScript payloads that execute in the context of the victim's browser session when they click on the link.

The attack requires user interaction, as the victim must click on a specially crafted URL or be redirected to one. The scope is changed, meaning the vulnerable component and impacted component are different—the vulnerable authentication endpoint allows attacks against the user's browser. While the httpOnly flag on session cookies prevents direct session hijacking, attackers can still perform significant malicious actions including credential phishing, UI modification, and data exfiltration of non-cookie browser data.

Root Cause

The root cause of this vulnerability is improper input validation and output encoding in the authentication endpoint. The application fails to:

1. Validate user input against expected patterns and character sets
2. Apply proper output encoding when reflecting user-supplied data in HTML responses
3. Implement Content Security Policy (CSP) headers that would mitigate script injection

This allows attackers to break out of the expected data context and inject executable JavaScript code that the browser interprets as legitimate application code.

Attack Vector

The attack is network-based and requires user interaction. An attacker would craft a malicious URL containing JavaScript payload in a vulnerable parameter of the authentication endpoint. The attack flow typically involves:

1. Attacker identifies the vulnerable parameter in the authentication endpoint
2. Attacker crafts a URL with embedded JavaScript payload
3. Attacker distributes the malicious URL via phishing emails, social engineering, or watering hole attacks
4. Victim clicks the link and navigates to the legitimate WSO2 application
5. The malicious JavaScript executes in the victim's browser with the origin of the trusted application
6. Attacker achieves their objective (redirect, UI manipulation, data theft, etc.)

For detailed technical information about exploitation, refer to the WSO2 Security Advisory WSO2-2025-4577.

Detection Methods for CVE-2025-10503

Indicators of Compromise

• Unusual URL parameters in authentication endpoint requests containing JavaScript-like syntax (e.g., <script>, javascript:, event handlers like onerror, onload)
• Requests to the authentication endpoint with URL-encoded payloads such as %3Cscript%3E or %22onclick%3D
• Anomalous redirect patterns originating from the authentication flow
• User reports of unexpected browser behavior during login

Detection Strategies

• Implement Web Application Firewall (WAF) rules to detect and block common XSS payloads in URL parameters
• Enable detailed logging on the authentication endpoint to capture suspicious request patterns
• Deploy endpoint detection solutions capable of identifying browser-based attacks and script injection attempts
• Review web server access logs for requests containing encoded or obfuscated JavaScript keywords

Monitoring Recommendations

• Monitor authentication endpoint traffic for abnormal parameter values or unusual character sequences
• Set up alerts for high volumes of failed or suspicious authentication attempts
• Track user complaints related to unexpected redirects or modified page content during login
• Implement real-time security monitoring for web application traffic anomalies

How to Mitigate CVE-2025-10503

Immediate Actions Required

• Apply the security patch provided by WSO2 as referenced in advisory WSO2-2025-4577
• Review and enhance input validation on all authentication endpoint parameters
• Implement strict Content Security Policy (CSP) headers to restrict inline script execution
• Conduct a security audit of other endpoints that may be similarly affected

Patch Information

WSO2 has released a security patch to address this vulnerability. Organizations should consult the WSO2 Security Advisory WSO2-2025-4577 for detailed patch information, affected versions, and upgrade instructions specific to their deployed WSO2 products.

Workarounds

• Deploy a Web Application Firewall (WAF) with XSS protection rules in front of the authentication endpoint
• Implement strict Content Security Policy headers that disable inline JavaScript execution: Content-Security-Policy: script-src 'self'
• Configure input validation at the reverse proxy or load balancer level to filter suspicious characters
• Educate users about the risks of clicking on links in unsolicited emails or messages

# Example Content Security Policy header configuration for Apache
# Add to httpd.conf or .htaccess
Header set Content-Security-Policy "default-src 'self'; script-src 'self'; style-src 'self' 'unsafe-inline'; img-src 'self' data:; frame-ancestors 'self';"
Header set X-XSS-Protection "1; mode=block"
Header set X-Content-Type-Options "nosniff"