CVE-2026-27398: RSVP Event Management Auth Bypass Flaw

CVE-2026-27398 Overview

CVE-2026-27398 is a Missing Authorization vulnerability [CWE-862] affecting the WP Chill RSVP and Event Management plugin for WordPress. The flaw exists in versions up to and including 2.7.16. Attackers can exploit incorrectly configured access control security levels to interact with plugin functionality that should be restricted. The vulnerability is exploitable over the network without authentication or user interaction.

Critical Impact
Unauthenticated attackers can access plugin functions intended to be restricted, leading to limited integrity impact on RSVP and event data managed by the affected WordPress sites.

Affected Products

WP Chill RSVP and Event Management plugin for WordPress
All versions from n/a through 2.7.16
WordPress sites running the vulnerable plugin

Discovery Timeline

2026-05-25 - CVE-2026-27398 published to NVD
2026-05-26 - Last updated in NVD database

Technical Details for CVE-2026-27398

Vulnerability Analysis

The vulnerability stems from a Missing Authorization weakness [CWE-862] in the RSVP and Event Management plugin. The plugin exposes functionality without verifying whether the requesting user holds the privileges required to invoke it. Attackers can issue network requests directly to vulnerable endpoints without authentication credentials.

The attack complexity is low, and no user interaction is required. The scope remains unchanged, and the impact is limited to integrity of plugin-managed data. Confidentiality and availability remain unaffected based on the published vector.

Root Cause

The root cause is an incorrectly configured access control check on plugin endpoints. The plugin fails to call capability or nonce verification functions such as current_user_can() or check_admin_referer() before performing privileged actions. This omission allows unauthenticated requests to reach handlers that should be reserved for authorized roles.

Attack Vector

An attacker sends crafted HTTP requests to the vulnerable plugin endpoints exposed by the WordPress site. Because no authentication is required, the attacker only needs network reachability to the target. Successful exploitation lets the attacker modify or create RSVP and event data managed by the plugin. See the Patchstack Vulnerability Report for additional technical context.

Detection Methods for CVE-2026-27398

Indicators of Compromise

Unexpected modifications to RSVP entries, event records, or attendee lists in the WordPress database.
Anonymous HTTP POST or GET requests targeting plugin endpoints under /wp-admin/admin-ajax.php or /wp-json/ routes registered by the RSVP plugin.
Spikes in unauthenticated requests originating from a single IP or short-lived IP ranges against plugin URLs.

Detection Strategies

Review WordPress access logs for requests to RSVP plugin endpoints lacking a valid authenticated session cookie.
Audit plugin-managed database tables for unauthorized insertions, deletions, or state changes against expected workflows.
Correlate WordPress activity logs with web server logs to identify suspicious request patterns matching unauthenticated administrative actions.

Monitoring Recommendations

Deploy a web application firewall (WAF) rule that flags or blocks unauthenticated requests to plugin admin-ajax actions associated with RSVP.
Enable a WordPress activity logging plugin to capture changes to events, RSVPs, and plugin settings.
Monitor outbound notifications such as RSVP confirmation emails for anomalies indicating attacker-induced state changes.

How to Mitigate CVE-2026-27398

Immediate Actions Required

Identify all WordPress sites running WP Chill RSVP and Event Management version 2.7.16 or earlier.
Update the plugin to a patched release once published by the vendor.
Restrict access to the WordPress admin and plugin endpoints behind a WAF or IP allowlist while patching is pending.

Patch Information

As of publication, fixes for versions beyond 2.7.16 are tracked through the Patchstack Vulnerability Report. Site administrators should apply the vendor patch immediately upon release and verify the installed plugin version through the WordPress admin dashboard.

Workarounds

Disable the RSVP and Event Management plugin until a patched version is available if event functionality is not business critical.
Apply WAF rules that deny unauthenticated requests to plugin endpoints handling RSVP and event modifications.
Limit access to /wp-admin/admin-ajax.php and plugin REST routes to authenticated sessions where feasible.

bash

# Configuration example: identify the installed plugin version via WP-CLI
wp plugin get rsvp --field=version
wp plugin update rsvp