CVE-2026-25136: Rucio WebUI Reflected XSS Vulnerability

CVE-2026-25136 Overview

A reflected Cross-Site Scripting (XSS) vulnerability has been identified in Rucio, a software framework that provides functionality to organize, manage, and access large volumes of scientific data using customizable policies. The vulnerability exists in the rendering of the ExceptionMessage within the WebUI 500 error page. This flaw could allow attackers to steal login session tokens from users who navigate to a specially crafted malicious URL.

Critical Impact

Attackers can exploit this reflected XSS vulnerability to steal user session tokens, potentially leading to account takeover and unauthorized access to sensitive scientific data managed by Rucio installations.

Affected Products

• Rucio versions prior to 35.8.3
• Rucio versions prior to 38.5.4
• Rucio versions prior to 39.3.1

Discovery Timeline

• 2026-02-25 - CVE-2026-25136 published to NVD
• 2026-02-25 - Last updated in NVD database

Technical Details for CVE-2026-25136

Vulnerability Analysis

This vulnerability is classified under CWE-79 (Improper Neutralization of Input During Web Page Generation), commonly known as Cross-Site Scripting. The flaw exists specifically within Rucio's WebUI error handling mechanism. When the application encounters a 500 Internal Server Error, it renders an error page that includes an ExceptionMessage. This message is not properly sanitized before being rendered in the user's browser, creating a reflected XSS attack vector.

The attack requires user interaction—specifically, the victim must click on or navigate to a maliciously crafted URL containing the XSS payload. Once executed, the injected script runs in the context of the victim's browser session with full access to the page's DOM, cookies, and session storage.

Root Cause

The root cause of this vulnerability is insufficient input validation and output encoding in the error page rendering functionality. When the WebUI generates the 500 error page, the ExceptionMessage parameter is incorporated into the HTML response without proper sanitization or encoding. This allows an attacker to inject arbitrary JavaScript code that executes when the error page is displayed to the victim.

Attack Vector

The attack is network-based and requires no prior authentication or special privileges. An attacker crafts a URL containing malicious JavaScript within parameters that ultimately get reflected in the ExceptionMessage field of the 500 error page. When a victim clicks this link, the malicious script executes in their browser context, allowing the attacker to:

1. Steal session cookies and authentication tokens
2. Perform actions on behalf of the authenticated user
3. Redirect users to malicious sites
4. Modify page content to conduct phishing attacks

The attack scenario typically involves social engineering to convince users to click the malicious link, often distributed via email, messaging platforms, or compromised websites. For detailed mitigation strategies against XSS attacks, see the OWASP Cross-Site Scripting Cheat Sheet.

Detection Methods for CVE-2026-25136

Indicators of Compromise

• Unusual HTTP requests to Rucio WebUI containing encoded JavaScript payloads in URL parameters
• Web server logs showing requests that result in 500 errors with suspicious query strings
• Users reporting unexpected behavior or redirections when accessing Rucio
• Authentication anomalies such as session tokens being used from unexpected IP addresses

Detection Strategies

• Implement Web Application Firewall (WAF) rules to detect and block common XSS payload patterns in incoming requests
• Monitor web server access logs for requests containing script tags, JavaScript event handlers, or encoded payloads targeting error pages
• Deploy browser security headers such as Content-Security-Policy to restrict script execution
• Use network intrusion detection systems (NIDS) signatures for known XSS attack patterns

Monitoring Recommendations

• Enable detailed logging on Rucio WebUI instances to capture full request URLs and parameters
• Set up alerts for high volumes of 500 errors, which may indicate exploitation attempts
• Monitor for exfiltration of session data to external domains
• Review authentication logs for suspicious session reuse patterns

How to Mitigate CVE-2026-25136

Immediate Actions Required

• Upgrade Rucio to patched versions 35.8.3, 38.5.4, or 39.3.1 immediately depending on your version branch
• Implement Content-Security-Policy headers to restrict inline script execution as a defense-in-depth measure
• Review access logs for any evidence of prior exploitation attempts
• Educate users about the risks of clicking suspicious links, especially those containing URL-encoded parameters

Patch Information

The Rucio development team has released security patches addressing this vulnerability. Organizations should upgrade to the following fixed versions based on their current deployment:

• For the 35.x branch: Upgrade to version 35.8.3
• For the 38.x branch: Upgrade to version 38.5.4
• For the 39.x branch: Upgrade to version 39.3.1

Full details about the vulnerability and remediation can be found in the GitHub Security Advisory GHSA-h79m-5jjm-jm4q.

Workarounds

• Deploy a Web Application Firewall (WAF) with XSS filtering rules to block malicious requests before they reach the application
• Implement strict Content-Security-Policy headers that disable inline script execution: script-src 'self'
• Place Rucio WebUI behind a reverse proxy that sanitizes or strips potentially malicious URL parameters
• Restrict access to Rucio WebUI to trusted networks via network segmentation until patching is complete

# Example Content-Security-Policy header configuration for Apache
# Add to Apache configuration or .htaccess file
Header set Content-Security-Policy "default-src 'self'; script-src 'self'; style-src 'self' 'unsafe-inline'; img-src 'self' data:; frame-ancestors 'none';"
Header set X-Content-Type-Options "nosniff"
Header set X-XSS-Protection "1; mode=block"