CVE-2025-53350 is a reflected Cross-site Scripting (XSS) vulnerability identified in the webjunk Calendar Plus product, affecting versions up to and including 1.2.4. The vulnerability stems from improper neutralization of input during web page generation, which allows malicious actors to inject and execute arbitrary JavaScript code in the context of a victim's browser when they interact with a crafted URL or input. This type of vulnerability is classified as reflected because the malicious payload is reflected off the web server in an immediate response, requiring user interaction to trigger. The CVSS 3.1 base score of 7.1 reflects a high severity, with attack vector being network (remote), low attack complexity, no privileges required, but user interaction necessary. The scope is changed (S:C), indicating that the vulnerability can affect resources beyond the initially vulnerable component. The impact affects confidentiality, integrity, and availability, as attackers can steal session cookies, perform actions on behalf of users, or cause denial of service. Although no public exploits are currently known, the vulnerability is published and should be addressed promptly. The lack of available patches in the provided data suggests that organizations should implement immediate mitigations while awaiting vendor updates. The vulnerability is particularly relevant for organizations relying on Calendar Plus for scheduling and collaboration, as exploitation could lead to unauthorized access or disruption of services.

For European organizations, exploitation of CVE-2025-53350 could lead to significant security breaches including theft of sensitive calendar data, session hijacking, and unauthorized actions performed under the guise of legitimate users. This can disrupt business operations, compromise confidential information, and damage trust in organizational IT systems. Given the collaborative nature of calendar applications, attackers could leverage this vulnerability to pivot into other internal systems or conduct targeted phishing campaigns. The reflected XSS nature means that social engineering is a key component of exploitation, increasing the risk to end users who may be tricked into clicking malicious links. Organizations in sectors such as finance, government, healthcare, and critical infrastructure in Europe, which often rely on secure scheduling tools, may face increased risks. Additionally, the vulnerability could be exploited to bypass security controls or deliver secondary payloads, amplifying its impact.

1. Apply vendor patches immediately once available to address the root cause of the vulnerability. 2. Implement strict input validation and output encoding on all user-supplied data to prevent script injection. 3. Deploy Content Security Policy (CSP) headers to restrict the execution of unauthorized scripts in browsers. 4. Use web application firewalls (WAFs) with updated signatures to detect and block reflected XSS attack patterns targeting Calendar Plus. 5. Educate users about the risks of clicking on unsolicited or suspicious links, especially those related to calendar invitations or scheduling. 6. Conduct regular security assessments and penetration testing focused on web application vulnerabilities. 7. Monitor logs for unusual activity or repeated attempts to exploit XSS vectors. 8. Consider isolating or sandboxing calendar application access to limit potential lateral movement if exploited.