CVE-2025-61676: October CMS XSS Vulnerability

CVE-2025-61676 Overview

A Cross-Site Scripting (XSS) vulnerability has been identified in October CMS, a popular Content Management System and web platform. The vulnerability exists in the backend configuration forms, specifically in the Branding & Appearance settings. A user with the "Customize Backend Styles" permission can inject malicious HTML/JavaScript into the stylesheet input field. The specially crafted input can break out of the intended <style> context, allowing arbitrary script execution across backend pages affecting all users.

Critical Impact

Authenticated attackers with specific permissions can inject malicious scripts that execute in the context of all backend users, potentially leading to session hijacking, credential theft, and unauthorized administrative actions.

Affected Products

• October CMS versions prior to 3.7.13
• October CMS versions prior to 4.0.12

Discovery Timeline

• 2026-01-10 - CVE CVE-2025-61676 published to NVD
• 2026-01-13 - Last updated in NVD database

Technical Details for CVE-2025-61676

Vulnerability Analysis

This stored XSS vulnerability (CWE-79) affects the backend configuration forms in October CMS. The vulnerability stems from insufficient input validation in the stylesheet input field within the Branding & Appearance settings. When a user with the "Customize Backend Styles" permission submits malicious content, the application fails to properly sanitize the input before rendering it within the <style> context.

The attack requires authentication and specific permissions, limiting the attack surface. However, once exploited, the injected script executes in the browser context of all users accessing the backend, making it a significant threat for multi-user October CMS installations.

Root Cause

The root cause is improper input sanitization in the stylesheet input field. The application does not adequately validate or encode user-supplied content before embedding it within HTML <style> tags. This allows an attacker to craft payloads that escape the style context using techniques such as closing the style tag and injecting script elements.

Attack Vector

The attack is network-based and requires the attacker to have authenticated access with the "Customize Backend Styles" permission. The attacker navigates to the Branding & Appearance settings in the October CMS backend and injects a malicious payload into the stylesheet input field. The payload breaks out of the <style> context by using HTML tag injection techniques, such as:

The malicious payload could close the existing <style> tag and inject arbitrary HTML/JavaScript elements. When other backend users access any backend page, the injected script executes in their browser context, potentially allowing the attacker to steal session cookies, perform actions on behalf of authenticated administrators, or modify page content.

For detailed technical information, refer to the GitHub Security Advisory.

Detection Methods for CVE-2025-61676

Indicators of Compromise

• Unexpected <script> tags or JavaScript event handlers in the custom stylesheet configuration stored in the database
• Unusual modifications to the Branding & Appearance settings by users with limited expected access
• Browser console errors or unexpected JavaScript execution on backend pages
• Session token exfiltration attempts in network logs originating from backend pages

Detection Strategies

• Monitor changes to backend configuration settings, particularly the Branding & Appearance stylesheet fields
• Implement Content Security Policy (CSP) headers to detect and block inline script execution
• Review audit logs for modifications to branding settings by users with the "Customize Backend Styles" permission
• Deploy web application firewalls (WAF) with XSS detection rules to identify suspicious payloads

Monitoring Recommendations

• Enable comprehensive logging for all backend configuration changes in October CMS
• Set up alerts for any modifications to the Styles configuration in Branding & Appearance
• Monitor for unusual user behavior patterns from accounts with elevated styling permissions
• Implement real-time browser-based XSS detection through CSP violation reporting

How to Mitigate CVE-2025-61676

Immediate Actions Required

• Upgrade October CMS to version 3.7.13 or later for the 3.x branch
• Upgrade October CMS to version 4.0.12 or later for the 4.x branch
• Audit current Branding & Appearance settings for any suspicious or unexpected content
• Review user permissions and restrict "Customize Backend Styles" access to trusted administrators only

Patch Information

October CMS has released security patches addressing this vulnerability. Users should upgrade to the following versions:

• Version 3.7.13 - Patched release for the 3.x branch
• Version 4.0.12 - Patched release for the 4.x branch

For detailed patch information and upgrade instructions, see the GitHub Security Advisory.

Workarounds

• Temporarily revoke the "Customize Backend Styles" permission from all users until patching is complete
• Implement strict Content Security Policy headers to mitigate the impact of any injected scripts
• Regularly audit and sanitize existing stylesheet configurations for malicious content
• Restrict backend access to trusted IP addresses as an additional layer of protection

# Configuration example - Review and restrict permissions
# In your October CMS backend, navigate to:
# Settings -> Administrators -> [User] -> Permissions
# 
# Uncheck "Customize Backend Styles" for non-essential users
# until the system is patched to version 3.7.13 or 4.0.12