CVE-2025-62499 is a stored cross-site scripting (XSS) vulnerability identified in Six Apart Ltd.'s Movable Type (Software Edition) affecting multiple versions including 7 r.5509 and earlier, 8.0.0 to 8.0.7, and 8.4.0 to 8.4.3. The flaw resides in the Edit CategorySet of ContentType page, where input fields do not properly sanitize or encode user-supplied data. An attacker possessing the "ContentType Management" privilege can craft and store malicious JavaScript payloads within this interface. When other users with access to this page load the affected content, the stored script executes in their browsers, potentially allowing the attacker to hijack sessions, steal cookies, perform actions on behalf of the victim, or deliver further malware. The vulnerability requires that the attacker already have elevated privileges (ContentType Management) and that the victim interacts with the vulnerable page, limiting the attack surface. The CVSS v3.0 score of 4.8 reflects a medium severity, with network attack vector, low attack complexity, high privileges required, and user interaction necessary. No public exploits or active exploitation have been reported to date. The vulnerability affects a widely used content management system, often deployed in corporate and publishing environments, making it a relevant concern for organizations relying on Movable Type for web content management. The lack of official patch links suggests that organizations should monitor vendor communications closely for updates or apply workarounds such as input validation and privilege restrictions.

For European organizations, this vulnerability poses a risk primarily to the confidentiality and integrity of web sessions and data managed through Movable Type. Exploitation could lead to unauthorized actions performed by attackers impersonating legitimate users, data leakage, or defacement of web content. Organizations in sectors such as media, publishing, and corporate communications that use Movable Type are at risk of reputational damage and operational disruption. Since the vulnerability requires elevated privileges, insider threats or compromised accounts with ContentType Management rights are the most likely vectors. The impact on availability is minimal, but the potential for lateral movement or further compromise through session hijacking elevates the risk. Given the medium severity and absence of known exploits, the immediate threat level is moderate; however, unpatched systems remain vulnerable to targeted attacks, especially in environments with less stringent access controls.

European organizations should implement the following specific mitigations: 1) Immediately audit and restrict ContentType Management privileges to only trusted personnel to reduce the attack surface. 2) Apply any official patches or updates from Six Apart Ltd. as soon as they become available. 3) Implement input validation and output encoding on the Edit CategorySet of ContentType page to prevent malicious script injection. 4) Monitor web application logs for unusual activity related to ContentType management functions. 5) Employ Content Security Policy (CSP) headers to limit the impact of potential XSS payloads. 6) Educate administrators and users with elevated privileges about the risks of XSS and safe handling of input fields. 7) Consider isolating or sandboxing the Movable Type management interface to limit exposure. 8) Regularly review and update web application firewall (WAF) rules to detect and block XSS attack patterns targeting Movable Type. These steps go beyond generic advice by focusing on privilege management, proactive monitoring, and layered defenses tailored to the vulnerability context.