CVE-2026-24838 is a critical vulnerability classified under CWE-79 (Improper Neutralization of Input During Web Page Generation), commonly known as cross-site scripting (XSS), found in the Dnn.Platform content management system. Dnn.Platform is an open-source CMS built on the Microsoft technology stack, widely used for managing web content. The vulnerability exists in the handling of module titles, which support rich text input. Prior to versions 9.13.10 and 10.2.0, these module titles could include embedded scripts that are not properly sanitized or neutralized, allowing malicious JavaScript code to execute in the context of the victim's browser. This flaw can be exploited by an attacker with authenticated access (high privileges) to inject scripts that execute without requiring user interaction, potentially leading to session hijacking, data theft, or further compromise of the web application and its users. The vulnerability affects versions earlier than 9.13.10 and versions from 10.0.0 up to but not including 10.2.0. The CVSS v3.1 base score is 9.1, indicating a critical severity with network attack vector, low attack complexity, high privileges required, no user interaction needed, and a scope change that impacts confidentiality, integrity, and availability. Although no known exploits have been reported in the wild, the potential impact is severe. The fix is included in versions 9.13.10 and 10.2.0, which properly sanitize module title inputs to prevent script execution.

For European organizations, this vulnerability poses a significant risk to web-based services relying on Dnn.Platform. Exploitation can lead to unauthorized disclosure of sensitive information, defacement of websites, session hijacking, and potentially full compromise of the CMS environment. This can disrupt business operations, damage reputation, and lead to regulatory non-compliance under GDPR due to data breaches. Public-facing portals, intranets, and extranets using vulnerable versions are particularly at risk. Since exploitation requires authenticated access with high privileges, insider threats or compromised credentials could be leveraged to launch attacks. The broad impact on confidentiality, integrity, and availability makes this a critical concern for sectors such as government, finance, healthcare, and critical infrastructure within Europe.

European organizations should immediately verify their Dnn.Platform versions and upgrade to 9.13.10 or 10.2.0 or later to apply the official patch. In addition to patching, organizations should audit all module titles and rich text inputs for malicious content and implement strict input validation and output encoding as defense-in-depth measures. Employing web application firewalls (WAFs) with custom rules to detect and block suspicious script injections can provide temporary protection. Limit administrative privileges and enforce strong authentication mechanisms to reduce the risk of credential compromise. Regularly monitor logs for unusual activities related to module title changes or script injections. Conduct security awareness training for administrators to recognize and prevent misuse of CMS features. Finally, maintain an incident response plan tailored for web application attacks to quickly contain and remediate any exploitation attempts.