CVE-2025-26923: Event Post Plugin Stored XSS Vulnerability

CVE-2025-26923 Overview

CVE-2025-26923 is a stored Cross-Site Scripting (XSS) vulnerability in the Bastien Ho Event post WordPress plugin. The flaw affects all plugin versions up to and including 5.9.8. Improper neutralization of user-supplied input during web page generation allows an authenticated attacker to inject persistent JavaScript payloads that execute in the browsers of users who view the affected pages.

The vulnerability is categorized under [CWE-79] (Improper Neutralization of Input During Web Page Generation).

Critical Impact

Authenticated attackers can store malicious scripts that run in visitor and administrator sessions, enabling session theft, unauthorized actions, and content manipulation across affected WordPress sites.

Affected Products

• Bastien Ho Event post WordPress plugin, versions up to and including 5.9.8
• WordPress installations with the vulnerable plugin activated
• Any site rendering event content authored through the plugin

Discovery Timeline

• 2025-03-26 - CVE-2025-26923 published to the National Vulnerability Database
• 2026-06-17 - Last updated in NVD database

Technical Details for CVE-2025-26923

Vulnerability Analysis

The Event post plugin fails to properly sanitize and encode user-supplied input before rendering it in generated web pages. An authenticated user with permission to create or edit event posts can embed HTML and JavaScript inside plugin-controlled fields. When another user loads the page containing that content, the browser parses and executes the injected script within the site's origin.

Because the payload is persisted in the database, exploitation does not require social-engineering delivery of a crafted URL. Every visitor to the affected event page becomes a target. The scope change reflected in the vulnerability profile indicates that stored scripts can affect resources beyond the initially compromised component, including administrator sessions.

Root Cause

The root cause is missing or insufficient output encoding on fields handled by the plugin. WordPress provides escaping helpers such as esc_html(), esc_attr(), and wp_kses_post() for context-appropriate sanitization. The affected plugin either omits these calls or applies them inconsistently, permitting raw HTML tags and event handlers to survive into the rendered DOM.

Attack Vector

Exploitation requires an authenticated account with permission to submit event content and requires a victim to view the page containing the payload. The attack is delivered over the network against the WordPress site. A typical scenario involves a contributor-level user inserting a <script> tag or DOM event handler such as onerror into an event field. When an editor or administrator later reviews the event, the payload executes with that user's privileges, enabling actions such as creating administrator accounts or exfiltrating session cookies.

Refer to the Patchstack XSS Vulnerability Report for additional technical context.

Detection Methods for CVE-2025-26923

Indicators of Compromise

• Event post entries containing <script> tags, javascript: URIs, or inline event handlers such as onerror, onload, or onmouseover.
• Unexpected administrator account creations or role changes shortly after event posts are viewed.
• Outbound requests from browsers of authenticated users to unfamiliar domains when accessing event pages.

Detection Strategies

• Audit the wp_posts and plugin-specific tables for stored HTML markup in fields that should contain plain text.
• Deploy Web Application Firewall (WAF) rules that flag script tags and encoded payloads submitted to plugin endpoints.
• Review WordPress access logs for POST requests to event submission endpoints from low-privilege accounts followed by admin page views.

Monitoring Recommendations

• Alert on modifications to wp_users and wp_usermeta tables that grant administrator capabilities.
• Monitor browser Content Security Policy (CSP) violation reports for inline script execution on event pages.
• Track plugin version inventory across managed WordPress sites to identify hosts running Event post5.9.8 or earlier.

How to Mitigate CVE-2025-26923

Immediate Actions Required

• Update the Event post plugin to a version later than 5.9.8 once the vendor publishes a patched release.
• Restrict event authoring permissions to trusted users until the plugin is updated.
• Review existing event posts for injected HTML or JavaScript and remove any malicious content.

Patch Information

At the time of the last NVD update on 2026-06-17, the vulnerability was reported to affect versions through 5.9.8. Consult the Patchstack XSS Vulnerability Report for the latest fixed version guidance from the vendor.

Workarounds

• Deactivate the Event post plugin until a fixed version is available if event functionality is not critical.
• Enforce a strict Content Security Policy that disallows inline scripts on pages rendering plugin output.
• Deploy WAF signatures that block XSS payloads targeting plugin submission endpoints.
• Reduce the number of accounts with contributor or higher roles to limit the pool of potential authenticated attackers.