CVE-2024-13431 is a reflected Cross-Site Scripting (XSS) vulnerability identified in the Appointment Booking Calendar — Simply Schedule Appointments Booking Plugin, also known as Simply Schedule Appointments, for WordPress. This vulnerability affects all plugin versions up to and including 1.6.8.3. The root cause is improper neutralization of input during web page generation, specifically insufficient sanitization and escaping of the 'accent_color' and 'background' URL parameters. An unauthenticated attacker can craft a malicious URL containing JavaScript payloads in these parameters. When a victim clicks this link, the injected script executes in the context of the victim's browser session on the affected WordPress site. This reflected XSS flaw can be leveraged to steal session cookies, perform actions on behalf of the user, or redirect users to malicious sites. The vulnerability does not require authentication but does require user interaction (clicking a link). The CVSS v3.1 base score is 6.1, indicating medium severity, with attack vector network, low attack complexity, no privileges required, user interaction required, and impacts on confidentiality and integrity but not availability. No public exploits have been reported yet, but the vulnerability is publicly disclosed and should be considered a significant risk for sites using this plugin. The plugin is widely used for appointment scheduling, making it a valuable target for attackers aiming to compromise business websites or their users. The vulnerability was published on March 7, 2025, and assigned by Wordfence. No official patches or updates are linked yet, so mitigation relies on workarounds or plugin updates once available.

This vulnerability poses a moderate risk to organizations using the Simply Schedule Appointments plugin on WordPress sites. Successful exploitation can lead to the execution of arbitrary JavaScript in the context of the affected site, enabling attackers to steal sensitive information such as session cookies, perform unauthorized actions on behalf of users, or redirect users to phishing or malware sites. This compromises the confidentiality and integrity of user data and can damage organizational reputation. While availability is not impacted, the potential for user account compromise or data leakage can have serious consequences, especially for businesses relying on appointment scheduling for customer interactions. The attack requires no authentication but does require user interaction, which may limit mass exploitation but still poses a significant risk through targeted phishing campaigns. Organizations with high traffic WordPress sites using this plugin, particularly in sectors like healthcare, legal, or professional services, may face increased risk. The absence of known exploits in the wild currently reduces immediate threat but does not eliminate the risk of future exploitation.

Organizations should immediately verify if they use the Appointment Booking Calendar — Simply Schedule Appointments Booking Plugin and identify the plugin version. Until an official patch is released, consider the following mitigations: 1) Implement Web Application Firewall (WAF) rules to detect and block requests containing suspicious payloads in the 'accent_color' and 'background' parameters. 2) Employ Content Security Policy (CSP) headers to restrict the execution of inline scripts and reduce the impact of XSS attacks. 3) Educate users and administrators about the risks of clicking unsolicited links, especially those targeting the affected parameters. 4) Monitor web server and application logs for unusual query parameters or repeated suspicious requests. 5) If feasible, temporarily disable or replace the vulnerable plugin with alternative appointment scheduling solutions until a secure update is available. 6) Follow vendor announcements closely and apply patches immediately once released. 7) Conduct regular security assessments and penetration tests focusing on input validation and output encoding in web applications. These targeted mitigations go beyond generic advice by focusing on the specific vulnerable parameters and practical interim controls.