CVE-2018-18872 in Calendar Plugin
Summary
by MITRE
The Kieran O'Shea Calendar plugin before 1.3.11 for WordPress has Stored XSS via the event_title parameter in a wp-admin/admin.php?page=calendar add action, or the category name during category creation at the wp-admin/admin.php?page=calendar-categories URI.
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Analysis
by VulDB Data Team • 09/15/2023
The CVE-2018-18872 vulnerability represents a critical stored cross-site scripting flaw in the Kieran O'Shea Calendar plugin for WordPress, affecting versions prior to 1.3.11. This vulnerability exposes WordPress sites to persistent malicious code execution through user input fields that are not properly sanitized or validated. The flaw manifests in two distinct attack vectors within the plugin's administrative interface, creating multiple pathways for threat actors to compromise the system. The vulnerability specifically targets the event_title parameter during event creation and the category name field during category creation, both occurring within the WordPress admin dashboard environment.
The technical implementation of this vulnerability stems from inadequate input validation and output sanitization within the plugin's backend processing. When administrators or users with appropriate privileges create calendar events or categories through the wp-admin interface, the plugin fails to properly escape or filter user-supplied data before storing it in the database. This stored data is then subsequently rendered in the web interface without proper HTML encoding, allowing malicious scripts to execute in the context of other users' browsers. The vulnerability operates at the application layer and directly impacts the integrity of the WordPress administrative environment, where trusted users interact with the system.
The operational impact of this vulnerability extends beyond simple data theft or defacement, as it provides attackers with the capability to execute arbitrary JavaScript code within the browser context of authenticated users. This creates a persistent threat vector where malicious actors can establish backdoors, steal session cookies, redirect users to malicious sites, or perform actions on behalf of legitimate users. The stored nature of the XSS vulnerability means that once exploited, the malicious payload remains active until the affected plugin is updated or the compromised data is manually removed from the database. This persistent threat poses significant risk to WordPress administrators and users who maintain calendar data through the vulnerable plugin.
Mitigation strategies for CVE-2018-18872 require immediate patching of the affected plugin to version 1.3.11 or later, which incorporates proper input sanitization and output escaping mechanisms. System administrators should conduct thorough security audits of their WordPress installations to identify all instances of the vulnerable plugin and ensure complete remediation. Additionally, implementing proper input validation at multiple layers, including database storage and output rendering, helps prevent similar vulnerabilities from emerging in other components. This vulnerability aligns with CWE-79, which describes cross-site scripting flaws, and represents a classic example of how insufficient sanitization of user inputs can create persistent security weaknesses in web applications. The ATT&CK framework categorizes this vulnerability under the T1059.007 technique for scripting, as it enables attackers to execute code through malicious script injection within the targeted environment.