CVE-2024-8477 Overview
CVE-2024-8477 is a Cross-Site Request Forgery (CSRF) vulnerability [CWE-352] affecting the Brevo (formerly Sendinblue) Newsletter, SMTP, Email Marketing and Subscribe Forms plugin for WordPress. The flaw exists in all versions up to and including 3.1.87. Missing or incorrect nonce validation on the Init() function allows unauthenticated attackers to disconnect a site's Brevo integration through a forged request. Exploitation requires tricking a site administrator into clicking a malicious link or visiting an attacker-controlled page.
Critical Impact
An attacker who successfully lures an authenticated administrator can terminate the Brevo API connection, disrupting newsletter delivery, transactional email, and marketing automation workflows.
Affected Products
- Brevo Newsletter, SMTP, Email Marketing and Subscribe Forms plugin for WordPress — all versions through 3.1.87
- WordPress sites using the mailin plugin package
- Fixed in plugin version 3.1.88
Discovery Timeline
- 2024-10-10 - CVE-2024-8477 published to the National Vulnerability Database (NVD)
- 2026-06-17 - Last updated in NVD database
Technical Details for CVE-2024-8477
Vulnerability Analysis
The vulnerability resides in the plugin's Init() function, which handles initialization actions including the disconnection of the Brevo API integration. The function processes state-changing requests without validating a WordPress nonce token. WordPress nonces are the standard defense against CSRF, tying a request to a specific user session and action.
Because the function trusts the request context, any authenticated administrator visiting an attacker-controlled page can trigger the disconnect action. The browser automatically supplies the administrator's authentication cookies, and the plugin executes the request as if the admin initiated it. The impact is limited to integrity — the Brevo connection state is altered — with no direct disclosure of confidential data.
Root Cause
The root cause is missing nonce verification in the Init() handler. Standard WordPress hardening requires calls to wp_verify_nonce() or check_admin_referer() before performing privileged state changes. The Brevo plugin omitted these checks on the initialization path that handles account disconnection, leaving the endpoint reachable by any request that arrives with a valid admin session cookie.
Attack Vector
Exploitation follows a classic CSRF pattern. An attacker crafts an HTML page containing an auto-submitting form or image tag targeting the vulnerable WordPress endpoint. The attacker delivers the link through phishing, forum posts, or comments. When a logged-in administrator loads the page, the browser issues the request with valid session cookies and the plugin executes the disconnect logic. No credentials, tokens, or prior access to the target site are required from the attacker.
The vulnerability mechanism is described in prose only; see the Wordfence Vulnerability Report and the WordPress Plugin Changeset for the patch diff.
Detection Methods for CVE-2024-8477
Indicators of Compromise
- Unexpected disconnection events for the Brevo API integration in WordPress admin logs
- HTTP requests to the Brevo plugin admin page originating from external Referer headers
- Administrator sessions loading third-party pages immediately before a Brevo disconnect event
- Sudden failure of newsletter or transactional email delivery without an administrator-initiated change
Detection Strategies
- Monitor WordPress audit logs for calls to the plugin's page-home.php handler that lack an associated nonce parameter
- Inspect web server access logs for POST or GET requests to Brevo plugin endpoints with off-site Referer values
- Correlate administrator browser activity with plugin state changes to identify request forgery patterns
Monitoring Recommendations
- Enable a WordPress activity logging plugin that records plugin configuration changes and administrator actions
- Alert on any Brevo integration disconnect or reconfiguration outside change windows
- Track outbound email delivery metrics and generate alerts on abrupt drops that may indicate a severed API link
How to Mitigate CVE-2024-8477
Immediate Actions Required
- Update the Brevo Newsletter, SMTP, Email Marketing and Subscribe Forms plugin to version 3.1.88 or later
- Audit administrator accounts and remove unused privileged users to reduce the CSRF attack surface
- Review recent Brevo connection state changes and reconnect the integration if disconnection is observed
- Educate administrators to avoid clicking untrusted links while logged into the WordPress admin console
Patch Information
The vendor released the fix in version 3.1.88. The patch is documented in the WordPress Plugin Changeset 3165451, which adds nonce validation to the affected initialization path. Site owners should apply the update through the WordPress plugin manager or WP-CLI.
Workarounds
- Restrict access to the WordPress admin interface using IP allowlisting at the web server or WAF layer
- Deploy a web application firewall rule that blocks requests to the Brevo plugin admin endpoints lacking a same-origin Referer header
- Require administrators to use dedicated browser profiles or sessions for WordPress administration to limit cross-site exposure
# Configuration example: update the plugin using WP-CLI
wp plugin update mailin --version=3.1.88
wp plugin list --name=mailin --fields=name,status,version
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
