External risk intelligence

The Events Calendar Unauthenticated PHP Object Injection Vulnerability

CVE advisorySeverity: CRITICAL (CVSS 9.8)

CVE-2026-78265

The vulnerability affects a WordPress plugin designed for event management. Such plugins are typically installed on web servers and are publicly accessible to site visitors to view or interact with event calendars, making the application's functionality internet-facing by default.

Deserialization

Halo Surface Signal: 4 out of 5 — likely to be public-facing.

External exposure likelihood

Horizon Alert

Summary of the vulnerability and why it matters

A critical vulnerability has been identified in a popular WordPress plugin for managing events. This flaw could allow unauthorized access and manipulation of systems if exploited, impacting the integrity and availability of data. The main concern is to confirm if this technology is in use and understand its potential exposure.

Unauthenticated code injection in event software.
Affects public-facing websites.
Confirm usage and assess exposure.

Attack Path

How an attacker could exploit the issue

An unauthenticated attacker can exploit this vulnerability by sending specially crafted data to a vulnerable WordPress website. This allows them to inject malicious PHP objects, potentially leading to the execution of arbitrary code on the server.

No authentication required.
Triggered via crafted data injection.
High risk of code execution.

Live Threat

Current exploitation, exposure, and threat context

This unauthenticated PHP Object Injection vulnerability could allow an attacker to execute arbitrary code on the server when the application unserializes malicious data. This could lead to a full compromise of the affected WordPress site, including data theft, modification, or deletion.

Server-side code execution.
Website data compromise.
Full site takeover.

Operational Fix

Recommended remediation, mitigation, and detection steps

This unauthenticated PHP Object Injection vulnerability in The Events Calendar affects web applications where the plugin is installed and publicly accessible. The primary responsibility for addressing this lies with the Application Owner or Web Development Team managing the WordPress site. The first critical step is to identify all instances of the affected plugin, confirm its reachability from the internet, and assess its business criticality. Once ownership and exposure are confirmed, remediation can be planned based on risk.

Application owners must address the issue.
Verify plugin reachability and criticality first.
Plan remediation based on verified risk.

Supplementary metadata

CVSS vector

Validate whether this threat affects your internet-facing exposure.

Halo Threat Intelligence helps prioritize remediation with Halo Surface Signal and H/A/L/O context. Start exposure validation with a free external attack surface trial.

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Frequently asked questions

What is The Events Calendar plugin?

The Events Calendar is a widely used WordPress plugin that helps site administrators organize, display, and manage event schedules. It is frequently employed by businesses, organizations, and community sites to provide visitors with interactive, public-facing calendars, allowing them to browse and RSVP for events directly through a web browser.

What does PHP Object Injection mean for CVE-2026-78265?

This vulnerability, classified as CWE-502 (Deserialization of Untrusted Data), occurs when the plugin improperly handles serialized information. By sending specially crafted data, an attacker can trick the system into creating unauthorized PHP objects. This weakness allows the attacker to manipulate how the application behaves, which can lead to the execution of arbitrary code on the underlying server.

How is this vulnerability triggered?

An attacker triggers this flaw by sending a specifically formatted request containing malicious data to a site running a vulnerable version of the plugin. Importantly, the vulnerability requires no user account or administrative privileges to initiate. Simply interacting with the public features of a site that processes this crafted input is sufficient to trigger the flaw; standard legitimate site traffic does not activate the vulnerability.

Is my website at risk from this vulnerability?

According to Halo Surface Signal, this plugin is typically installed on web servers where it is internet-facing by default, meaning it is accessible to any visitor. Because the vulnerability does not require authentication, any WordPress site running the affected versions is reachable by external parties. If your site uses this plugin to display calendars to the public, it is likely exposed to this threat.

Do I need to take action if I use this plugin?

Yes. Your first priority is to create an inventory of all your WordPress sites to confirm which ones have The Events Calendar installed. Determine if the plugin is active and reachable via the internet. Once you have confirmed where it is running, verify the version number. This allows your team to prioritize updates or protective measures for the most critical sites first.

References

patchstack.com/database/wordpress/plugin/the-events-calendar/vulnera…

Written by Nicholas Merritt

Nicholas Merritt is VP of Security Solutions at Halo Security. With more than 25 years across application security, vulnerability prioritization, and offensive security, he helps teams translate threat data into practical exposure validation and remediation focus. He authors Halo Threat Intelligence CVE advisories using Halo Surface Signal and H/A/L/O context to prioritize internet-facing risk.