CVE-2023-4635 in EventON Plugin
Summary
by MITRE • 10/25/2023
The EventON plugin for WordPress is vulnerable to Reflected Cross-Site Scripting via the 'tab' parameter in versions up to, and including, 2.2.2 due to insufficient input sanitization and output escaping. This makes it possible for unauthenticated attackers to inject arbitrary web scripts in pages that execute if they can successfully trick a user into performing an action such as clicking on a link.
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Analysis
by VulDB Data Team • 04/10/2026
The EventON plugin for WordPress represents a widely used calendar management solution that has been identified with a critical reflected cross-site scripting vulnerability affecting versions up to and including 2.2.2. This vulnerability stems from inadequate input validation and output escaping mechanisms within the plugin's codebase, specifically concerning the 'tab' parameter handling. The flaw allows malicious actors to inject arbitrary JavaScript code that executes in the context of a victim's browser when they interact with specially crafted URLs. The vulnerability's classification aligns with CWE-79 which addresses improper neutralization of input during web page generation, making it particularly dangerous in web applications where user input is directly rendered without proper sanitization. The reflected nature of this XSS vulnerability means that the malicious script is reflected off the web server rather than being stored, making it easier to deliver through social engineering tactics such as phishing emails or compromised websites.
The operational impact of this vulnerability extends beyond simple script execution as it creates a vector for more sophisticated attacks that can compromise user sessions, steal sensitive information, or redirect users to malicious sites. Attackers can craft payloads that exploit the 'tab' parameter to inject malicious scripts that persist in the user's browser session, potentially leading to session hijacking or credential theft. The vulnerability affects unauthenticated attackers, meaning no prior access or credentials are required to exploit the issue, which significantly increases its attack surface. This weakness directly relates to ATT&CK technique T1566.001 which covers phishing with malicious attachments, as attackers can leverage the vulnerability to create convincing phishing campaigns that appear legitimate to end users. The reflected nature also makes it particularly challenging to detect through traditional security monitoring as the malicious payloads are not stored on the server but rather injected into the response stream during dynamic page generation.
Mitigation strategies for this vulnerability must address both immediate remediation and long-term security hardening measures. The most critical immediate action involves updating to the latest version of the EventON plugin where the XSS vulnerability has been patched through proper input sanitization and output escaping. Administrators should also implement Content Security Policy headers to limit the execution of unauthorized scripts, though this provides defense-in-depth rather than a complete solution. Input validation should be strengthened to ensure all user-supplied parameters including the 'tab' parameter undergo rigorous sanitization before being processed or rendered in web pages. The vulnerability demonstrates the importance of following secure coding practices such as those outlined in the OWASP Secure Coding Practices, specifically the principle of least privilege and proper input validation. Organizations should also consider implementing web application firewalls that can detect and block suspicious parameter patterns, and conduct regular security assessments of WordPress plugins to identify similar vulnerabilities. Additionally, user education regarding suspicious links and email attachments remains crucial as social engineering remains a primary delivery method for exploiting such XSS vulnerabilities. The incident highlights the necessity of continuous security monitoring and vulnerability management processes to ensure timely patch deployment and prevent exploitation of known vulnerabilities in widely used web applications.