CVE-2025-56536: OpenNebula Stored XSS Vulnerability

CVE-2025-56536 Overview

A stored cross-site scripting (XSS) vulnerability has been identified in OpenNebula v6.10.0.1. This vulnerability allows attackers to execute arbitrary web scripts or HTML by injecting a crafted payload into the user information parameter. As a stored XSS vulnerability, malicious scripts persist in the application's database and execute whenever other users access the affected page, making it particularly dangerous in multi-user cloud management environments.

Critical Impact
Attackers can persistently inject malicious scripts that execute in the context of other users' sessions, potentially leading to session hijacking, credential theft, or unauthorized actions within the OpenNebula cloud management platform.

Affected Products

OpenNebula v6.10.0.1

Discovery Timeline

2026-04-29 - CVE CVE-2025-56536 published to NVD
2026-04-29 - Last updated in NVD database

Technical Details for CVE-2025-56536

Vulnerability Analysis

This stored XSS vulnerability (CWE-79) exists within OpenNebula's user information handling mechanism. The application fails to properly sanitize user-supplied input before storing it in the database and subsequently rendering it in web pages. When malicious script code is injected into the user information parameter, it is stored persistently and executed in the browsers of any users who view the affected content.

The attack can be executed over the network and requires user interaction (a victim must view the page containing the malicious payload). The vulnerability has a changed scope, meaning the malicious script executes within the context of the vulnerable web application but can affect resources beyond its security scope, potentially impacting other users' sessions and data.

Root Cause

The root cause of this vulnerability is improper input validation and output encoding in OpenNebula's user information handling functionality. The application does not adequately sanitize special characters (such as <, >, ", and ') in user-supplied data before storing it in the database or rendering it in HTML context. This allows attackers to inject HTML tags and JavaScript code that the browser interprets and executes as part of the legitimate page content.

Attack Vector

The attack is executed over the network with low complexity. An attacker with access to OpenNebula can craft a malicious payload containing JavaScript code and inject it into the user information parameter. Since this is a stored XSS vulnerability, the payload persists in the application's database. When other authenticated users access pages that display the compromised user information, their browsers execute the attacker's malicious script. This can lead to session token theft, phishing attacks, defacement, or performing unauthorized actions on behalf of the victim user.

The vulnerability exploits insufficient input sanitization in the user profile or user information fields. Attackers typically inject payloads such as script tags or event handlers that execute when the content is rendered in a victim's browser.

Detection Methods for CVE-2025-56536

Indicators of Compromise

Unexpected JavaScript code or HTML tags present in user information fields within the OpenNebula database
Anomalous user profile data containing encoded script payloads (e.g., <script>, <img onerror=, javascript:)
Browser console errors or unexpected script execution when viewing user profiles or related pages
Reports of suspicious behavior or unauthorized actions from legitimate users after viewing certain pages

Detection Strategies

Implement Web Application Firewall (WAF) rules to detect and block common XSS payloads in HTTP requests targeting user information endpoints
Monitor application logs for requests containing suspicious characters or encoded script patterns in user input fields
Deploy Content Security Policy (CSP) headers with violation reporting to detect attempted script injections
Conduct regular database audits to identify stored payloads containing HTML or JavaScript in user information fields

Monitoring Recommendations

Enable detailed logging for all user profile modification requests and review logs for injection attempts
Configure browser-side monitoring through CSP report-uri directives to capture XSS attempt notifications
Implement real-time alerting for database insertions containing potential XSS patterns in user-controlled fields

How to Mitigate CVE-2025-56536

Immediate Actions Required

Upgrade OpenNebula to version 7.x or later, which addresses this vulnerability according to the OpenNebula Release Announcement
Review existing user information entries in the database and sanitize any suspicious content
Implement Content Security Policy (CSP) headers to mitigate the impact of successful XSS attacks
Restrict access to user profile modification features until patching is complete

Patch Information

OpenNebula has released version 7.x which addresses security issues present in earlier versions. Administrators should upgrade to the latest stable release available from the official OpenNebula repositories. For detailed technical information about this vulnerability, refer to the GitHub PoC for CVE-2025-56536.

Workarounds

Implement strict input validation on user information fields, rejecting or encoding special characters such as <, >, ", ', and &
Deploy a Web Application Firewall (WAF) with XSS protection rules in front of OpenNebula instances
Enable Content Security Policy headers with script-src 'self' to prevent inline script execution
Limit user profile editing capabilities to trusted administrators until the patch can be applied

bash

# Example Content Security Policy header configuration for Apache
# Add to your OpenNebula virtual host configuration
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-Content-Type-Options "nosniff"
Header set X-XSS-Protection "1; mode=block"