CVE-2024-31378: Mailmunch Mailchimp Forms CSRF Vulnerability

CVE-2024-31378 Overview

CVE-2024-31378 is a Cross-Site Request Forgery (CSRF) vulnerability affecting the MailChimp Forms by MailMunch plugin for WordPress. The flaw impacts all versions through 3.2.1. An attacker can craft a malicious request that, when triggered by an authenticated administrator visiting an attacker-controlled page, performs privileged actions inside the plugin without the victim's consent.

Critical Impact
Successful exploitation allows an unauthenticated attacker to leverage a logged-in administrator's session to alter plugin state, leading to high impact on confidentiality, integrity, and availability of the affected WordPress site.

Affected Products

MailMunch MailChimp Forms by MailMunch WordPress plugin
All versions from n/a through 3.2.1
WordPress sites running the vulnerable plugin with authenticated administrator users

Discovery Timeline

2024-04-15 - CVE-2024-31378 published to NVD
2026-04-28 - Last updated in NVD database

Technical Details for CVE-2024-31378

Vulnerability Analysis

The vulnerability is classified under [CWE-352] Cross-Site Request Forgery. The MailChimp Forms by MailMunch plugin fails to validate the origin or authenticity of state-changing HTTP requests sent to its administrative endpoints. WordPress provides nonces and the check_admin_referer() API to defend against this class of issue, but the affected plugin code paths do not enforce these checks before performing sensitive actions.

Exploitation requires user interaction. An attacker must convince an authenticated administrator to visit a malicious page or click a crafted link while logged in to WordPress. The browser automatically attaches the administrator's session cookies, allowing the forged request to execute with full administrator privileges.

The Patchstack advisory rates the issue with high impact on confidentiality, integrity, and availability, consistent with attacker-controlled modification of plugin configuration on a WordPress installation. The current EPSS probability is low, indicating limited observed exploitation attempts.

Root Cause

The root cause is missing or improperly verified anti-CSRF tokens on plugin request handlers. Sensitive actions exposed by the plugin accept requests based solely on the user's authenticated session, without validating a per-request nonce tied to the originating page.

Attack Vector

The attack vector is network-based and requires no privileges, but it does require user interaction from an authenticated administrator. The attacker hosts a page containing an auto-submitting form or fetch request targeting the vulnerable plugin endpoint. When the administrator loads the page, the browser issues the request with valid session cookies, and the plugin executes the action.

The vulnerability is described in prose because no public proof-of-concept code is referenced in the advisory. See the Patchstack CSRF Vulnerability Advisory for technical details.

Detection Methods for CVE-2024-31378

Indicators of Compromise

Unexpected configuration changes in MailChimp Forms by MailMunch plugin settings
HTTP POST requests to plugin admin endpoints with Referer headers pointing to external domains
Administrator account activity originating from sessions immediately after visits to untrusted sites
New or modified forms, integrations, or API keys within the plugin that administrators did not create

Detection Strategies

Inspect web server access logs for requests to MailChimp Forms by MailMunch admin handlers that lack expected nonce parameters such as _wpnonce
Compare Referer and Origin headers on plugin state-changing requests against the site's own hostname
Correlate WordPress audit log entries for plugin configuration changes with administrator browsing telemetry

Monitoring Recommendations

Enable a WordPress audit logging plugin to record changes to MailMunch settings and form definitions
Forward web server and WordPress logs to a centralized analytics platform such as Singularity Data Lake for correlation across endpoint and web telemetry
Alert on administrator HTTP sessions that issue plugin write requests from external referrers

How to Mitigate CVE-2024-31378

Immediate Actions Required

Update the MailChimp Forms by MailMunch plugin to a version newer than 3.2.1 as soon as a fixed release is available from the vendor
Restrict WordPress administrator accounts to a minimum and require these users to avoid browsing untrusted sites while authenticated
Enforce two-factor authentication for all administrator accounts to reduce session abuse risk
Audit recent plugin configuration changes and revert any unauthorized modifications

Patch Information

Review the Patchstack CSRF Vulnerability Advisory for current vendor patch status. Apply the fixed plugin release through the WordPress admin update interface or via WP-CLI once published.

Workarounds

Temporarily deactivate the MailChimp Forms by MailMunch plugin if a patched version is not yet available
Use a web application firewall to block requests to plugin admin endpoints when the Referer or Origin header does not match the site domain
Require administrators to log out of WordPress before browsing external sites, or use a dedicated browser profile for administrative tasks

bash

# Update the plugin once a fixed version is published
wp plugin update mailchimp-forms-by-mailmunch

# Temporary workaround: deactivate the plugin until patched
wp plugin deactivate mailchimp-forms-by-mailmunch