CVE-2025-62499 is a stored cross-site scripting (XSS) vulnerability identified in Six Apart Ltd.'s Movable Type (Software Edition), specifically within the Edit CategorySet of ContentType page. The vulnerability allows an attacker who possesses the ContentType Management privilege to inject crafted malicious scripts into the system. These scripts are stored persistently and executed in the web browsers of users who access the affected page, potentially leading to session hijacking, credential theft, or unauthorized actions performed in the context of the victim's session. The vulnerability affects multiple versions of Movable Type, including the 7 series (up to r.5509), 8.0 series (8.0.0 to 8.0.7), and 8.4 series (8.4.0 to 8.4.3). The CVSS 3.0 base score is 4.8, indicating medium severity, with the vector highlighting network attack vector, low attack complexity, high privileges required, user interaction needed, and a scope change. Although no known exploits are currently reported in the wild, the vulnerability's nature as stored XSS means it could be leveraged for persistent attacks against users with access to the ContentType management interface. The attack requires the attacker to have elevated privileges, limiting the attack surface to insiders or compromised accounts. The vulnerability impacts confidentiality and integrity but does not affect availability. Since Movable Type is used for content management, exploitation could lead to defacement, data leakage, or further compromise through chained attacks.

For European organizations using Movable Type, this vulnerability poses a risk primarily to the confidentiality and integrity of their content management systems. Attackers with ContentType Management privileges could inject malicious scripts that execute in the browsers of other privileged users, potentially leading to session hijacking, unauthorized data access, or manipulation of content. This could result in reputational damage, data breaches, and compliance violations under regulations such as GDPR. The impact is heightened in organizations where Movable Type is used for critical content publishing or internal communications. Since the vulnerability requires high privileges and user interaction, the risk is somewhat contained but still significant in environments with multiple administrators or editors. The absence of known exploits reduces immediate risk but does not eliminate the threat, especially given the persistent nature of stored XSS. European entities with public-facing or internal Movable Type deployments should consider this vulnerability a moderate threat that could be leveraged in targeted attacks or insider threats.

To mitigate CVE-2025-62499, European organizations should first apply any available patches or updates from Six Apart Ltd. If patches are not yet available, organizations should restrict the ContentType Management privilege to the minimum number of trusted users to reduce the attack surface. Implement strict input validation and sanitization on all user inputs related to ContentType management to prevent injection of malicious scripts. Employ Content Security Policy (CSP) headers to limit the execution of unauthorized scripts in browsers. Regularly audit and monitor logs for suspicious activities related to ContentType editing pages. Educate administrators and content managers about the risks of XSS and the importance of cautious input handling. Consider deploying web application firewalls (WAFs) with rules targeting XSS payloads specific to Movable Type. Finally, conduct periodic security assessments and penetration tests focusing on CMS components to detect and remediate similar vulnerabilities proactively.