CVE-2023-51295 is a medium severity vulnerability affecting PHPJabbers Event Booking Calendar version 4.0. The vulnerability involves multiple HTML injection flaws in several input parameters, specifically "name", "plugin_sms_api_key", "plugin_sms_country_code", and "title". HTML injection occurs when an attacker is able to inject arbitrary HTML or script code into web pages viewed by other users, potentially leading to cross-site scripting (XSS) or other client-side attacks. In this case, the injection points are parameters that are likely used to capture user input or configuration values related to event booking and SMS plugin settings. The CVSS 3.1 base score of 6.5 reflects a network exploitable vulnerability (AV:N) with low attack complexity (AC:L), no privileges required (PR:N), and no user interaction needed (UI:N). The impact affects confidentiality and integrity but not availability. The CWE-77 classification indicates improper neutralization of special elements used in a command (in this case, HTML content). Although no known exploits are reported in the wild, the vulnerability could allow an attacker to inject malicious HTML or scripts, potentially leading to session hijacking, defacement, or redirection attacks. The lack of vendor or product details beyond PHPJabbers Event Booking Calendar v4.0 limits precise contextualization, but the affected parameters suggest that the vulnerability could be exploited remotely via crafted HTTP requests without authentication or user interaction.

For European organizations using PHPJabbers Event Booking Calendar v4.0, this vulnerability poses a risk of client-side attacks such as session hijacking, phishing, or unauthorized data manipulation through injected HTML or scripts. This can lead to compromised user accounts, leakage of sensitive booking or customer data, and damage to organizational reputation. Since the vulnerability requires no authentication or user interaction, attackers can exploit it remotely, increasing the risk of widespread abuse. Organizations relying on this calendar for event management, ticketing, or customer engagement could see disruptions or data integrity issues. Additionally, if the SMS plugin parameters are exploited, attackers might manipulate SMS-related functionalities, potentially causing misinformation or unauthorized notifications. The confidentiality and integrity impacts could also affect compliance with GDPR and other European data protection regulations, leading to legal and financial consequences.

To mitigate this vulnerability, organizations should immediately apply any available patches or updates from PHPJabbers for the Event Booking Calendar. If patches are not yet available, implement strict input validation and output encoding on all affected parameters ("name", "plugin_sms_api_key", "plugin_sms_country_code", "title") to neutralize any HTML or script content. Employ Content Security Policy (CSP) headers to restrict the execution of unauthorized scripts in the web application. Conduct thorough code reviews and penetration testing focusing on injection points to identify and remediate similar issues. Additionally, monitor web server logs for suspicious requests targeting these parameters and implement Web Application Firewall (WAF) rules to block malicious payloads. Educate developers and administrators about secure coding practices related to input sanitization and parameter handling. Finally, consider isolating or disabling the SMS plugin functionality if it is not critical, to reduce the attack surface.