CVE-2026-23840 identifies a critical security vulnerability in the Movary web application, a platform designed for tracking, rating, and exploring movie watch histories. The root cause is improper input validation (CWE-20) of the 'categoryDeleted' URL parameter, which allows attackers to inject arbitrary JavaScript code, resulting in a cross-site scripting (XSS) vulnerability (CWE-79). This vulnerability affects all Movary versions prior to 0.70.0. An attacker can craft a malicious URL containing a payload in the 'categoryDeleted' parameter and trick users into clicking it. Upon execution, the malicious script can hijack user sessions, steal cookies, manipulate the DOM, or perform actions on behalf of the user, compromising confidentiality and integrity. The vulnerability does not require authentication (PR:N) but does require user interaction (UI:R). The CVSS 3.1 score of 9.3 reflects the network attack vector (AV:N), low attack complexity (AC:L), and high impact on confidentiality and integrity (C:H/I:H), with no impact on availability (A:N). Although no public exploits are currently known, the vulnerability is publicly disclosed and fixed in Movary version 0.70.0. The absence of patch links suggests users should upgrade to the latest version directly from the vendor. The vulnerability's scope is limited to web clients interacting with the vulnerable parameter, but the impact on user data and trust is significant.

For European organizations, the impact of CVE-2026-23840 can be substantial, particularly for those using Movary as part of their digital entertainment or media management infrastructure. Successful exploitation can lead to theft of user credentials, session hijacking, and unauthorized actions performed in the context of the victim's session. This can result in data breaches involving personal user information, loss of user trust, and potential regulatory repercussions under GDPR due to compromised personal data. Additionally, attackers could use the XSS vulnerability as a pivot point for further attacks, such as delivering malware or phishing campaigns targeting European users. The vulnerability's network-based attack vector means it can be exploited remotely without authentication, increasing the risk of widespread exploitation if not promptly addressed. Organizations relying on Movary for internal or public-facing services may face reputational damage and operational disruptions if users are compromised. The lack of known exploits in the wild currently reduces immediate risk but does not eliminate the threat, especially given the public disclosure and availability of technical details.

European organizations should immediately upgrade Movary installations to version 0.70.0 or later, where the vulnerability is patched. In addition to upgrading, organizations should implement strict input validation and sanitization on all user-supplied data, particularly URL parameters like 'categoryDeleted'. Deploying a robust Content Security Policy (CSP) can help mitigate the impact of XSS by restricting the execution of unauthorized scripts. Web Application Firewalls (WAFs) configured to detect and block XSS payloads targeting Movary can provide an additional layer of defense. Regular security audits and penetration testing focusing on input validation should be conducted to identify similar vulnerabilities. User education on the risks of clicking untrusted links can reduce the likelihood of successful exploitation. Monitoring web server logs for suspicious requests containing unusual 'categoryDeleted' parameter values can help detect attempted attacks. Finally, organizations should ensure incident response plans include procedures for handling XSS incidents to minimize damage.