EUVD-2026-42852
GHSA-x463-v9cq-m85h
Severity by source
AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
Network-accessible unauthenticated AJAX endpoint (AV:N, PR:N); no complexity barriers; user click required (UI:R); injected script executes in victim browser context, changing scope (S:C) with limited session/content impact (C:L/I:L).
Primary rating from Vendor (Wordfence).
CVSS VectorVendor: Wordfence
Lifecycle Timeline
2DescriptionCVE.org
The ICS Calendar plugin for WordPress is vulnerable to Reflected Cross-Site Scripting via the 'htmltagtitle' parameter in all versions up to, and including, 12.0.9 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. The vulnerability is reachable via the unauthenticated wp_ajax_nopriv_r34ics_ajax AJAX action, which accepts attacker-controlled js_args values merged over stored shortcode configuration without nonce verification, allowing the htmltagtitle key to bypass the normal shortcode allowlist check.
AnalysisAI
Reflected XSS in the ICS Calendar WordPress plugin (all versions ≤ 12.0.9) allows unauthenticated network attackers to inject arbitrary JavaScript into victim browsers by exploiting a missing nonce check and input sanitization failure on the publicly accessible wp_ajax_nopriv_r34ics_ajax AJAX endpoint. The attacker-controlled js_args object is merged over stored shortcode configuration before allowlist validation, enabling the htmltagtitle key to reach the calendar-month.php template unescaped. No public exploit code or CISA KEV listing exists at time of analysis, though the scope-changing CVSS vector (S:C) and zero authentication barrier make socially engineered delivery via crafted URLs a realistic threat to any site running this plugin.
Technical ContextAI
CWE-79 (Improper Neutralization of Input During Web Page Generation - Cross-Site Scripting) describes the root cause: attacker input is reflected into page output without adequate sanitization or encoding. The ICS Calendar plugin (CPE: cpe:2.3:a:room34:ics_calendar:*:*:*:*:*:*:*:*) registers the wp_ajax_nopriv_r34ics_ajax WordPress AJAX action, which is accessible to unauthenticated users by design. The vulnerable handler in r34ics-ajax.php (lines 33, 53, 72) accepts a js_args JSON payload and merges it over the plugin's stored shortcode configuration object without first verifying a WordPress nonce. Because the merge occurs before the shortcode parameter allowlist is evaluated, the htmltagtitle key is carried through to the calendar rendering template (templates/calendar-month.php:40) where it is written into the HTML output without output escaping. This is a classic parameter-injection path: a server-side object merge that allows attacker-controlled keys to override or introduce configuration values that were intended to be developer-controlled, bypassing the allowlist gate that would otherwise block arbitrary keys.
RemediationAI
Update the ICS Calendar plugin to the version released after the patch commit recorded in the WordPress Subversion repository changeset at https://plugins.trac.wordpress.org/changeset?reponame=&old=3563728%40ics-calendar&new=3563728%40ics-calendar; the exact patched release version number is not independently confirmed from the available data, so administrators should check the WordPress.org plugin directory for the current release and upgrade accordingly. If immediate patching is not possible, deactivating the plugin eliminates the entire attack surface with no side effects beyond loss of calendar functionality. Sites that must keep the plugin active while awaiting a patch can deploy a WAF rule blocking requests to wp-admin/admin-ajax.php where the action parameter equals r34ics_ajax and the request body or query string contains a htmltagtitle key - note this will break legitimate AJAX calendar rendering. Implementing a strict Content-Security-Policy header (script-src 'self') limits the damage of any successful XSS execution by preventing inline script and off-origin resource loading, though this may require testing for compatibility with other site components.
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External POC / Exploit Code
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