CVE-2024-21911 is a stored cross-site scripting (XSS) vulnerability classified under CWE-79 that affects TinyMCE versions before 5.6.0. TinyMCE is a widely used web-based rich text editor integrated into numerous content management systems, web applications, and SaaS platforms. The vulnerability arises from improper neutralization of input during web page generation, allowing an unauthenticated and remote attacker to inject crafted HTML content into the editor. When other users load or interact with the compromised content, the malicious JavaScript executes in their browsers, potentially leading to session hijacking, credential theft, or execution of further malicious actions within the context of the affected web application. The vulnerability does not require authentication but does require user interaction to trigger the payload. The CVSS 3.1 score is 6.1, reflecting medium severity with network attack vector, low attack complexity, no privileges required, but requiring user interaction. The scope is changed (S:C), indicating that the vulnerability affects resources beyond the initially vulnerable component. There are no known exploits in the wild as of the published date, but the risk remains significant due to the widespread use of TinyMCE. No official patch links were provided in the source, but upgrading to version 5.6.0 or later is recommended to remediate the issue. Additional mitigations include input sanitization and deployment of Content Security Policy (CSP) headers to reduce the impact of potential exploitation.

For European organizations, this vulnerability poses a risk primarily to web applications and services that embed TinyMCE versions prior to 5.6.0. Exploitation can lead to unauthorized script execution in users' browsers, enabling attackers to steal session cookies, perform actions on behalf of users, or deliver further malware. This can compromise confidentiality and integrity of user data and organizational information. Given the prevalence of TinyMCE in enterprise content management, e-commerce, and customer portals, the impact could extend to sensitive business operations and customer trust. The vulnerability does not affect availability directly but can facilitate broader attacks that degrade service or cause reputational damage. Organizations in sectors with high regulatory requirements for data protection, such as finance, healthcare, and government, face increased compliance risks if exploited. The requirement for user interaction means phishing or social engineering could be used to trigger the attack, increasing the threat surface. Overall, the vulnerability could enable attackers to bypass security controls and escalate privileges within web environments used by European entities.

1. Upgrade TinyMCE to version 5.6.0 or later immediately to apply the official fix for this vulnerability. 2. Implement strict input validation and sanitization on all user-generated content before it is stored or rendered by the editor to prevent injection of malicious HTML or scripts. 3. Deploy Content Security Policy (CSP) headers to restrict the execution of unauthorized scripts and reduce the impact of potential XSS attacks. 4. Conduct regular security audits and penetration testing focused on web application components using TinyMCE to identify residual risks. 5. Educate users about the risks of interacting with suspicious content and implement anti-phishing measures to reduce the likelihood of triggering malicious payloads. 6. Monitor web application logs and user activity for unusual behavior indicative of exploitation attempts. 7. If upgrading is not immediately feasible, consider disabling or restricting the use of TinyMCE in sensitive contexts until patched. 8. Collaborate with software vendors and service providers to ensure timely updates and security patches are applied.