CVE-2025-56537: OpenNebula Stored XSS Vulnerability

CVE-2025-56537 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 virtual network template parameter. The flaw persists in the application's storage layer, meaning malicious scripts are executed whenever affected content is rendered by other users viewing the compromised resource.

Critical Impact

Attackers can leverage this stored XSS vulnerability to steal session cookies, hijack user accounts, redirect users to malicious sites, or perform actions on behalf of authenticated users within the OpenNebula cloud management interface.

Affected Products

• OpenNebula v6.10.0.1
• OpenNebula versions prior to v7.0

Discovery Timeline

• 2026-04-29 - CVE-2025-56537 published to NVD
• 2026-04-29 - Last updated in NVD database

Technical Details for CVE-2025-56537

Vulnerability Analysis

This stored XSS vulnerability (CWE-79) resides in OpenNebula's virtual network template handling mechanism. Unlike reflected XSS attacks that require victim interaction with a malicious URL, stored XSS payloads are permanently saved within the application's database and automatically executed when users access the affected resource through normal application workflows.

The vulnerability specifically targets the virtual network template parameter functionality within OpenNebula's cloud management interface. When administrators or users create or modify virtual network templates, insufficient input sanitization allows JavaScript or HTML code to be embedded within template parameters. This malicious code is then stored server-side and rendered without proper encoding when other users view or interact with the affected virtual network template.

The attack requires network access and user interaction, as victims must navigate to pages that render the compromised virtual network template data. However, the scope is changed, meaning the vulnerability can impact resources beyond the original security boundary of the vulnerable component.

Root Cause

The root cause of this vulnerability is improper neutralization of input during web page generation. The OpenNebula application fails to adequately validate, sanitize, or encode user-supplied input within the virtual network template parameter before storing it in the database and subsequently rendering it in the user interface. This allows attackers to inject executable script content that bypasses the application's security controls.

Attack Vector

The attack is executed over the network and requires the attacker to have sufficient privileges to create or modify virtual network templates within the OpenNebula environment. The attacker crafts a malicious payload containing JavaScript or HTML code and injects it into a virtual network template parameter field. Once stored, any user with access to view the affected template will have the malicious script executed in their browser context.

The exploitation flow involves:

1. Attacker gains access to the OpenNebula interface with template creation/modification privileges
2. Attacker injects malicious script code into a virtual network template parameter
3. The payload is stored in the application database without proper sanitization
4. When other users view the compromised template, the malicious script executes in their browser
5. Attacker can steal session tokens, perform unauthorized actions, or redirect users to malicious sites

Technical details and proof-of-concept information are available in the GitHub PoC Repository.

Detection Methods for CVE-2025-56537

Indicators of Compromise

• Unusual JavaScript or HTML content within virtual network template parameters
• Session cookies or authentication tokens being transmitted to external domains
• Unexpected DOM modifications or script injections in OpenNebula web interface pages
• User reports of unusual behavior, redirects, or pop-ups when viewing virtual network templates

Detection Strategies

• Implement web application firewall (WAF) rules to detect common XSS patterns in requests to OpenNebula endpoints
• Monitor application logs for suspicious input patterns containing script tags, event handlers, or encoded JavaScript payloads
• Deploy content security policy (CSP) headers and monitor violation reports for script execution attempts
• Conduct regular security audits of stored template data for malicious content

Monitoring Recommendations

• Enable detailed logging for all template creation and modification operations in OpenNebula
• Configure alerting for CSP violation reports that may indicate XSS exploitation attempts
• Monitor outbound network connections from user browsers accessing the OpenNebula interface for data exfiltration indicators
• Implement real-time scanning of user input for known XSS payload signatures

How to Mitigate CVE-2025-56537

Immediate Actions Required

• Upgrade OpenNebula to version v7.0 or later, which contains the fix for this vulnerability
• Review existing virtual network templates for potentially malicious content and sanitize or remove compromised entries
• Implement Content Security Policy headers to mitigate the impact of any stored XSS payloads
• Restrict template creation and modification privileges to trusted administrators only

Patch Information

The vulnerability has been addressed in OpenNebula v7.0. Organizations running vulnerable versions should upgrade to the patched release as soon as possible. Release information and upgrade instructions are available in the OpenNebula Release Notes.

Workarounds

• Deploy a web application firewall (WAF) with XSS protection rules in front of the OpenNebula interface
• Implement strict Content Security Policy headers to prevent inline script execution
• Conduct a security review of all existing virtual network templates and remove any suspicious content
• Limit user permissions for template creation and modification to reduce the attack surface

For environments where immediate patching is not feasible, implementing defense-in-depth measures through WAF rules and CSP headers can help reduce exploitation risk while planning the upgrade to OpenNebula v7.0.