CVE-2023-51296 identifies a Cross-Site Scripting (XSS) vulnerability in PHPJabbers Event Booking Calendar version 4.0. The vulnerability arises from insufficient input sanitization and output encoding in several parameters: 'name', 'plugin_sms_api_key', 'plugin_sms_country_code', and 'title'. These parameters are likely used in the calendar's user interface or backend plugin configurations, where malicious input can be injected and subsequently executed in the context of a victim's web browser. This type of vulnerability is classified under CWE-79, which is a common web application security weakness allowing attackers to execute arbitrary JavaScript code. The CVSS 3.1 base score is 6.1 (medium), reflecting that the attack vector is network-based (remote), requires no privileges, but does require user interaction, and the impact affects confidentiality and integrity with no impact on availability. The scope is changed, indicating that the vulnerability can affect components beyond the initially vulnerable module, potentially impacting other parts of the application or user sessions. No patches or known exploits are currently documented, but the risk remains significant given the widespread use of PHPJabbers products in event management scenarios. Attackers could leverage this vulnerability to perform session hijacking, steal sensitive user data, or conduct phishing attacks by injecting malicious scripts. The lack of authentication requirement lowers the barrier for exploitation, but the need for user interaction means attackers must trick users into clicking malicious links or visiting compromised pages. The vulnerability was reserved in December 2023 and published in February 2025, indicating recent discovery and disclosure.

For European organizations, this vulnerability can lead to unauthorized disclosure of sensitive information such as session cookies, personal data, or credentials if exploited via XSS attacks. Event booking platforms often handle user registrations, payment information, and personal details, so exploitation could compromise user privacy and trust. Attackers could manipulate event details or inject malicious content, damaging organizational reputation and potentially leading to financial losses. Since the vulnerability affects web-facing components, it increases the attack surface for phishing campaigns targeting event attendees or administrators. The medium severity suggests a moderate risk, but the widespread use of PHPJabbers software in Europe, especially in sectors like education, hospitality, and public services, amplifies the potential impact. Additionally, the vulnerability could be chained with other exploits to escalate privileges or conduct further attacks within the network. Organizations failing to mitigate this risk may face regulatory consequences under GDPR due to inadequate protection of personal data processed through the affected applications.

Organizations should immediately audit their use of PHPJabbers Event Booking Calendar v4.0 and identify if the vulnerable parameters are exposed to user input. Implement strict input validation and output encoding on all affected parameters ('name', 'plugin_sms_api_key', 'plugin_sms_country_code', 'title') to neutralize malicious scripts. Deploy or update Web Application Firewalls (WAFs) with rules specifically targeting XSS attack patterns related to these parameters. Monitor web server logs and application behavior for unusual or suspicious requests that may indicate exploitation attempts. If possible, isolate the event booking application within a segmented network zone to limit lateral movement in case of compromise. Educate users and administrators about the risks of clicking untrusted links or submitting unverified data. Engage with PHPJabbers support or community forums to obtain or request official patches or updates addressing this vulnerability. Finally, consider implementing Content Security Policy (CSP) headers to restrict the execution of unauthorized scripts on affected web pages.