October CMS is a popular content management system and web platform used for building websites and web applications. CVE-2025-61676 is a cross-site scripting (XSS) vulnerability classified under CWE-79, discovered in the backend configuration forms of October CMS versions prior to 3.7.13 and 4.0.12. The vulnerability arises from improper neutralization of input during web page generation, specifically in the stylesheet input field under the Branding & Appearance settings. Users with the 'Customize Backend Styles' permission can inject malicious HTML or JavaScript code into this input. Because the input is intended to be placed within a <style> tag, a crafted payload can break out of this context, allowing the injection of executable script code. This results in arbitrary script execution on backend pages, affecting all users who access these pages. The attack requires authenticated access with elevated permissions and user interaction to trigger the malicious payload. The vulnerability does not affect the public-facing frontend but compromises the backend environment, potentially leading to session hijacking, privilege escalation, or further backend compromise. The issue was patched in October CMS versions 3.7.13 and 4.0.12 by properly sanitizing and restricting the input to prevent script injection. No known exploits have been reported in the wild, but the vulnerability poses a significant risk to organizations relying on vulnerable October CMS versions for their web infrastructure.

For European organizations using October CMS versions prior to 3.7.13 or 4.0.12, this vulnerability could lead to significant security risks within their backend management interfaces. Successful exploitation allows attackers with specific backend permissions to execute arbitrary JavaScript, potentially leading to session hijacking, unauthorized actions, or further compromise of administrative accounts. This could result in data breaches, defacement, or disruption of web services. Since the vulnerability requires authenticated access with the 'Customize Backend Styles' permission, insider threats or compromised accounts pose a particular risk. The impact is heightened for organizations with multiple backend users or those that grant broad permissions. Given the widespread use of October CMS in Europe for various web applications, especially in small to medium enterprises and public sector websites, the vulnerability could affect critical infrastructure and sensitive data. However, the lack of known exploits in the wild and the requirement for elevated permissions somewhat limit the immediate risk. Nonetheless, unpatched systems remain vulnerable to targeted attacks or insider misuse.

1. Immediately upgrade October CMS installations to version 3.7.13 or 4.0.12 or later to apply the official patch addressing this vulnerability. 2. Review and restrict backend user permissions, ensuring only trusted users have the 'Customize Backend Styles' permission. 3. Implement strict access controls and multi-factor authentication (MFA) for all backend users to reduce the risk of account compromise. 4. Conduct regular audits of backend user activities and permissions to detect any unauthorized changes or suspicious behavior. 5. Employ Content Security Policy (CSP) headers to limit the impact of potential XSS attacks by restricting script execution sources. 6. Monitor logs for unusual backend activity or attempts to inject malicious styles or scripts. 7. Educate backend users about the risks of XSS and the importance of cautious input handling. 8. If patching is temporarily not possible, consider disabling or limiting access to the Branding & Appearance settings for non-essential users as a temporary workaround.