CVE-2026-25735: Rucio WebUI Stored XSS Vulnerability

CVE-2026-25735 Overview

CVE-2026-25735 is a stored Cross-Site Scripting (XSS) vulnerability affecting 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 Identity Name field of the WebUI where attacker-controlled input is persisted by the backend and later rendered without proper output encoding.

This stored XSS vulnerability allows malicious JavaScript code to be executed in the context of the WebUI for any user who views the affected pages. The persistent nature of this vulnerability makes it particularly concerning as the malicious payload is stored server-side and executed every time a victim accesses the compromised page.

Critical Impact

Successful exploitation enables arbitrary JavaScript execution in victims' browsers, potentially allowing session token theft, unauthorized actions on behalf of authenticated users, and further compromise of scientific data management operations.

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-2026-25735 published to NVD
• 2026-02-26 - Last updated in NVD database

Technical Details for CVE-2026-25735

Vulnerability Analysis

The vulnerability is classified as CWE-79 (Improper Neutralization of Input During Web Page Generation), commonly known as Cross-Site Scripting. In this case, the vulnerability manifests as a stored XSS condition where malicious input submitted to the Identity Name field is persisted in the backend database without proper sanitization. When other users subsequently view pages that display this Identity Name, the unsanitized content is rendered directly into the HTML response without proper output encoding, causing the browser to execute embedded JavaScript code.

The attack requires network access and some level of privileged access to submit the malicious Identity Name value. However, once stored, the payload executes automatically for any user viewing the affected content, requiring no additional interaction beyond page viewing.

Root Cause

The root cause of this vulnerability is the lack of proper output encoding when rendering user-supplied Identity Name values in the WebUI. The backend correctly stores the data, but the frontend fails to encode special characters (such as <, >, ", and ') when inserting the Identity Name into HTML contexts. This allows an attacker to inject arbitrary HTML and JavaScript that will be executed in victims' browsers.

Attack Vector

The attack leverages the network-accessible WebUI interface. An attacker with sufficient privileges to modify Identity Name values can inject malicious JavaScript payloads. The attack flow proceeds as follows:

1. An authenticated attacker with appropriate permissions submits a crafted Identity Name containing JavaScript code
2. The backend persists this value without modification
3. When any user accesses a page displaying the compromised Identity Name, the WebUI renders the malicious content without encoding
4. The victim's browser executes the injected JavaScript in the context of the authenticated session

The malicious JavaScript could steal session tokens, perform actions as the victim user, redirect users to phishing pages, or exfiltrate sensitive data visible in the WebUI. For organizations managing large volumes of scientific data, this could lead to unauthorized access to research datasets or manipulation of data management policies.

Detection Methods for CVE-2026-25735

Indicators of Compromise

• Unusual or suspicious strings in Identity Name fields containing HTML tags or JavaScript syntax (e.g., <script>, onerror=, javascript:)
• Unexpected outbound connections from client browsers to external domains when viewing Rucio WebUI pages
• Reports from users of unusual behavior or pop-ups when accessing identity-related pages
• Audit logs showing Identity Name modifications with encoded or script-like content

Detection Strategies

• Implement Content Security Policy (CSP) headers to detect and block inline script execution attempts
• Deploy Web Application Firewall (WAF) rules to identify XSS payload patterns in submitted form data
• Enable browser-based XSS auditors and monitor for violations
• Review application logs for Identity Name submissions containing suspicious characters or encoded script content

Monitoring Recommendations

• Configure alerting on any Identity Name field containing common XSS vectors such as <script, javascript:, onerror, or onload
• Monitor network traffic for unusual data exfiltration patterns from WebUI sessions
• Implement real-time monitoring of CSP violation reports to identify attempted exploitation

How to Mitigate CVE-2026-25735

Immediate Actions Required

• Upgrade Rucio to version 35.8.3, 38.5.4, or 39.3.1 depending on your current version branch
• Audit existing Identity Name values in the database for potentially malicious content
• Implement Content Security Policy headers to provide defense-in-depth against XSS attacks
• Review access controls to limit which users can modify Identity Name fields

Patch Information

Rucio has released security patches addressing this vulnerability across multiple version branches. Organizations should upgrade to the appropriate fixed version:

• Rucio Release 35.8.3 - For users on the 35.x branch
• Rucio Release 38.5.4 - For users on the 38.x branch
• Rucio Release 39.3.1 - For users on the 39.x branch

Additional technical details and guidance are available in the GitHub Security Advisory GHSA-8wpv-6x3f-3rm5. For general XSS prevention best practices, refer to the OWASP XSS Prevention Cheat Sheet.

Workarounds

• Implement strict input validation on Identity Name fields to reject potentially malicious characters and patterns
• Deploy a Web Application Firewall (WAF) with XSS detection rules in front of the Rucio WebUI
• Configure restrictive Content Security Policy headers to prevent inline script execution
• Limit access to Identity Name modification functionality to only trusted administrative users until patching is complete

# Example Content Security Policy header configuration for Apache
# Add to your 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:; object-src 'none';"