CVE-2025-67551 is a Stored Cross-site Scripting (XSS) vulnerability identified in the Wappointment plugin developed by the Wappointment team, affecting versions up to 2.6.9. The vulnerability stems from improper neutralization of user-supplied input during the generation of web pages, which allows malicious scripts to be injected and stored persistently within the application. When other users access the affected pages, the malicious scripts execute in their browsers, potentially leading to session hijacking, credential theft, unauthorized actions on behalf of users, or defacement of the website. Stored XSS is particularly dangerous because the payload is saved on the server and delivered to multiple users, increasing the attack surface. No CVSS score has been assigned yet, and no known exploits are currently in the wild. However, the vulnerability is publicly disclosed and published on December 9, 2025, indicating that attackers could develop exploits soon. Wappointment is a WordPress plugin commonly used for appointment scheduling, and its user base includes various organizations that rely on it for client interactions. The lack of patches or mitigation details in the report suggests that users should be vigilant and prepare to apply updates once available. The vulnerability does not require authentication or user interaction to exploit, increasing its risk profile. The improper input neutralization likely involves failure to sanitize or encode input fields that are rendered in HTML contexts, a common cause of XSS vulnerabilities.

For European organizations using Wappointment, this vulnerability poses significant risks to confidentiality, integrity, and user trust. Attackers exploiting this flaw could steal session cookies, enabling unauthorized access to user accounts and sensitive data. This could lead to data breaches involving personal or financial information, especially critical for sectors like healthcare, legal, or financial services that may use appointment scheduling plugins. Additionally, attackers could perform actions on behalf of legitimate users, potentially disrupting business operations or damaging reputations through website defacement. The stored nature of the XSS increases the likelihood of widespread impact across multiple users. Given the plugin’s integration with WordPress, a widely used CMS in Europe, the scope of affected systems could be substantial. The absence of known exploits currently provides a window for mitigation, but the public disclosure increases the urgency for proactive defense. Failure to address this vulnerability could also lead to regulatory compliance issues under GDPR if personal data is compromised.

Organizations should immediately inventory their WordPress installations to identify the presence and version of the Wappointment plugin. Until an official patch is released, implement Web Application Firewall (WAF) rules to detect and block typical XSS payloads targeting Wappointment input fields. Employ strict Content Security Policies (CSP) to restrict the execution of unauthorized scripts. Review and harden input validation and output encoding practices within the plugin’s configuration if customization is possible. Monitor logs and user reports for suspicious activities indicative of XSS exploitation. Educate users and administrators about the risks of clicking suspicious links or submitting untrusted input. Once a patch is available, prioritize timely updates to the Wappointment plugin. Additionally, consider isolating or limiting the plugin’s permissions to reduce potential damage. Regular backups and incident response plans should be updated to handle potential exploitation scenarios.