CVE-2026-14827 in Calendar Plugin
Summary
by MITRE • 07/27/2026
The Calendar WordPress plugin before 1.3.18 does not properly escape a user-supplied event field before outputting it inside an HTML attribute on a public-facing page, allowing users with the Contributor role to inject arbitrary JavaScript that executes in the browser of anyone viewing the calendar.
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Analysis
by VulDB Data Team • 07/27/2026
The vulnerability in the Calendar WordPress plugin affects versions prior to 1.3.18 and represents a classic cross-site scripting flaw that enables unauthorized code execution through user-controlled input fields. This issue specifically occurs when event data submitted by users with the Contributor role is processed and displayed on public-facing calendar pages without proper HTML attribute escaping. The security implications are significant as it allows attackers to inject malicious javascript code that executes in the browsers of all visitors who view the affected calendar content, creating a persistent threat vector that can compromise user sessions and potentially exfiltrate sensitive information.
The technical flaw stems from improper input validation and output escaping mechanisms within the plugin's rendering logic. When users with Contributor privileges create or modify events through the WordPress admin interface, the event field data is stored in the database without adequate sanitization for HTML contexts. During page generation, this unsanitized data flows directly into HTML attributes without proper escaping, violating fundamental web security principles and creating an XSS vulnerability that can be exploited by any authenticated user with minimal privileges. This represents a CWE-79: Cross-site Scripting vulnerability where the application fails to properly escape output destined for HTML contexts.
The operational impact of this vulnerability extends beyond simple script injection as it creates a persistent threat that can affect all website visitors without requiring additional authentication or privilege escalation. Attackers can craft malicious event descriptions containing javascript payloads that execute whenever calendar pages are viewed, potentially leading to session hijacking, credential theft, or redirection to malicious sites. The low privilege requirement means that even users with minimal permissions can establish this attack vector, making it particularly dangerous for websites where multiple contributors have access to the calendar functionality.
Mitigation strategies should focus on implementing proper input sanitization and output escaping mechanisms throughout the plugin's data processing pipeline. The immediate solution involves updating to version 1.3.18 or later where the vulnerability has been patched through proper HTML attribute escaping of user-supplied content. Additional defensive measures include implementing Content Security Policy headers to limit script execution, restricting Contributor role permissions for calendar functionality, and conducting regular security audits of plugin code to identify similar output escaping issues. This vulnerability aligns with ATT&CK technique T1566.002: Phishing via Service Provider, as it enables attackers to create persistent phishing vectors through calendar content that can compromise visitors' browsers.