CVE-2025-53350 is a reflected Cross-site Scripting (XSS) vulnerability found in webjunk's Calendar Plus plugin, affecting all versions up to and including 1.2.4. The vulnerability stems from improper neutralization of user-supplied input during the generation of web pages, which allows attackers to inject malicious JavaScript code that is reflected back to users without proper sanitization. When a victim clicks a crafted URL or interacts with a maliciously crafted input, the injected script executes in the victim's browser context, potentially leading to session hijacking, credential theft, or unauthorized actions performed on behalf of the user. The CVSS v3.1 base score is 7.1, reflecting a high severity due to the network attack vector, low attack complexity, no required privileges, but requiring user interaction and having a scope change. The vulnerability affects confidentiality, integrity, and availability as attackers can steal sensitive data, manipulate user sessions, or disrupt service. Although no known exploits are currently in the wild, the vulnerability is publicly disclosed and should be addressed promptly. The plugin is commonly used in web applications for calendar management, making it a relevant target for attackers aiming to compromise web portals or intranet systems.

For European organizations, this vulnerability poses a significant risk especially for those relying on the Calendar Plus plugin for internal or customer-facing calendar functionalities. Exploitation can lead to unauthorized access to user sessions, leakage of sensitive information, and potential lateral movement within networks if attackers leverage stolen credentials. This can disrupt business operations, damage reputation, and lead to regulatory non-compliance under GDPR due to data breaches. The reflected XSS nature means phishing campaigns can be highly effective, increasing the risk of widespread compromise. Organizations with public-facing web applications or intranet portals using Calendar Plus are particularly vulnerable. The impact is heightened in sectors with sensitive data such as finance, healthcare, and government services prevalent in Europe.

1. Immediately update Calendar Plus to a patched version once available from the vendor. If no patch is currently available, consider disabling the plugin temporarily. 2. Implement strict input validation and output encoding on all user-supplied data within the application to prevent script injection. 3. Deploy a Web Application Firewall (WAF) with rules to detect and block reflected XSS attack patterns targeting Calendar Plus endpoints. 4. Conduct security awareness training for users to recognize and avoid clicking suspicious links that could trigger reflected XSS attacks. 5. Use Content Security Policy (CSP) headers to restrict the execution of unauthorized scripts in browsers. 6. Regularly audit and monitor web application logs for unusual activities or attempted exploit patterns related to Calendar Plus. 7. Employ multi-factor authentication (MFA) to reduce the impact of stolen credentials resulting from session hijacking.