CVE-2026-49765: Mailchimp Integration Auth Bypass Flaw

CVE-2026-49765 Overview

CVE-2026-49765 is an unauthenticated PHP Object Injection vulnerability in the WordPress plugin Integration for Mailchimp and Contact Form 7, WPForms, Elementor, Ninja Forms. All versions through 1.1.8 are affected. The flaw maps to [CWE-502: Deserialization of Untrusted Data] and allows network-based exploitation without authentication or user interaction. Successful exploitation can compromise confidentiality, integrity, and availability of the underlying WordPress site.

Critical Impact
Unauthenticated attackers can inject crafted PHP objects to trigger property-oriented programming (POP) chains, potentially leading to remote code execution, arbitrary file operations, or full site takeover.

Affected Products

WordPress plugin: Integration for Mailchimp and Contact Form 7, WPForms, Elementor, Ninja Forms
All versions <= 1.1.8
WordPress sites with the cf7-mailchimp plugin installed and active

Discovery Timeline

2026-06-15 - CVE-2026-49765 published to NVD
2026-06-17 - Last updated in NVD database

Technical Details for CVE-2026-49765

Vulnerability Analysis

The vulnerability is a PHP Object Injection flaw caused by insecure deserialization of attacker-controlled input. The plugin passes untrusted data into PHP's unserialize() function without validating the structure or class types of the serialized payload. An unauthenticated attacker reaching the affected endpoint over the network can submit a crafted serialized string. PHP then instantiates arbitrary objects and invokes their magic methods such as __wakeup(), __destruct(), or __toString().

When a suitable POP gadget chain exists in WordPress core, other plugins, or loaded libraries, this primitive escalates into file writes, SQL execution, or remote code execution. The Exploit Prediction Scoring System places this CVE in the 29.967 percentile with a probability of 0.383%, but the impact profile remains severe given the lack of authentication.

Root Cause

The root cause is the use of PHP deserialization on data sourced from HTTP request parameters within the cf7-mailchimp plugin. The plugin does not enforce an allowlist of safe classes and does not validate input as structured data such as JSON. Any serialized object the attacker supplies is reconstructed by the PHP runtime.

Attack Vector

Attackers deliver the exploit over HTTP or HTTPS to a public-facing WordPress site. The request contains a serialized PHP object payload in a parameter consumed by the vulnerable plugin code path. No credentials, tokens, or user interaction are required. When combined with a POP chain from another component on the host, the attacker achieves code execution under the web server user. Refer to the Patchstack WordPress Vulnerability advisory for additional technical details.

Detection Methods for CVE-2026-49765

Indicators of Compromise

HTTP requests to plugin endpoints containing serialized PHP markers such as O:, a:, or s: followed by integer:string patterns in POST or GET parameters.
Unexpected creation or modification of PHP files under wp-content/uploads/ or plugin directories.
New administrator accounts or modified wp_options rows in the WordPress database without a corresponding admin session.
Outbound connections from the web server to unfamiliar IPs shortly after suspicious POST requests to cf7-mailchimp endpoints.

Detection Strategies

Inspect web server and WAF logs for request bodies containing PHP serialization signatures targeting plugin handlers.
Monitor PHP error logs for __wakeup(), __destruct(), or class-not-found warnings originating from the plugin context.
Enable file integrity monitoring across the WordPress installation to detect unauthorized PHP file changes.

Monitoring Recommendations

Centralize WordPress, PHP-FPM, and web server logs into a SIEM and alert on serialized payload patterns.
Track plugin version inventory across all WordPress instances and alert when cf7-mailchimp <= 1.1.8 is detected.
Baseline normal form submission payloads and alert on anomalously long or binary-shaped parameter values.

How to Mitigate CVE-2026-49765

Immediate Actions Required

Update the Integration for Mailchimp and Contact Form 7, WPForms, Elementor, Ninja Forms plugin to a version newer than 1.1.8 as soon as a fixed release is published by the vendor.
If no fixed version is available, deactivate and remove the plugin from all WordPress sites.
Audit the WordPress installation for unauthorized administrator accounts, scheduled tasks, and modified PHP files.

Patch Information

Consult the Patchstack advisory for the current patched version and vendor remediation guidance. Apply updates through the WordPress plugin dashboard or via wp-cli once available.

Workarounds

Deploy a Web Application Firewall rule that blocks request parameters containing PHP serialization patterns such as O:\d+:" and a:\d+:\{.
Restrict access to the plugin's AJAX and form submission endpoints via IP allowlisting where feasible.
Disable the plugin until a verified patch is installed if the affected functionality is non-critical.

bash

# Example wp-cli commands to inventory and disable the vulnerable plugin
wp plugin list --name=cf7-mailchimp --fields=name,status,version
wp plugin deactivate cf7-mailchimp
wp plugin delete cf7-mailchimp