CVE-2026-1051: Newsletter WordPress Plugin CSRF Vulnerability

CVE-2026-1051 Overview

CVE-2026-1051 is a Cross-Site Request Forgery (CSRF) vulnerability in the Newsletter – Send awesome emails from WordPress plugin. The flaw affects all versions up to and including 9.1.0. The vulnerability stems from missing or incorrect nonce validation in the hook_newsletter_action() function. Unauthenticated attackers can unsubscribe newsletter subscribers through forged requests if they trick a logged-in user into clicking a malicious link. The issue is tracked under [CWE-352] and impacts integrity of subscription data without affecting confidentiality or availability.

Critical Impact

Attackers can forcibly unsubscribe newsletter subscribers by tricking authenticated users into visiting attacker-controlled pages, disrupting communication workflows for affected WordPress sites.

Affected Products

• Newsletter – Send awesome emails from WordPress plugin
• All versions up to and including 9.1.0
• WordPress sites running the vulnerable plugin

Discovery Timeline

• 2026-01-20 - CVE-2026-1051 published to NVD
• 2026-04-15 - Last updated in NVD database

Technical Details for CVE-2026-1051

Vulnerability Analysis

The Newsletter plugin exposes the hook_newsletter_action() function without enforcing proper anti-CSRF protections. WordPress provides a nonce framework specifically designed to validate that state-changing requests originate from legitimate user interactions. The plugin's unsubscription handler in unsubscription/unsubscription.php fails to apply this validation correctly. As a result, the server processes unsubscription actions based solely on session cookies and request parameters. An attacker can host a page containing an automatic request to the vulnerable endpoint. When an authenticated user visits the page, the browser submits the request with the user's session, and the plugin processes the unsubscribe action.

Root Cause

The root cause is missing or incorrect nonce verification on the hook_newsletter_action() function. WordPress plugins must call wp_verify_nonce() or check_admin_referer() to confirm that requests originate from the intended interface. The unsubscription handler omits this check, leaving the action endpoint reachable through forged cross-origin requests. See the WordPress Plugin Code Reference for the affected code path.

Attack Vector

Exploitation requires user interaction. The attacker crafts a malicious web page or email containing a link or auto-submitting form pointing to the vulnerable unsubscription endpoint. When a logged-in subscriber or administrator clicks the link, the browser sends authenticated cookies along with the forged request. The plugin processes the unsubscribe operation without validating request origin. The attack does not require credentials and operates over the network. Refer to the Wordfence Vulnerability Report for additional exploitation context.

Detection Methods for CVE-2026-1051

Indicators of Compromise

• Unexpected spikes in subscriber unsubscribe events without corresponding user-initiated actions
• Web server access logs showing requests to the Newsletter plugin unsubscription endpoint with external Referer headers
• Subscriber complaints about being unsubscribed without their consent

Detection Strategies

• Monitor HTTP requests targeting the Newsletter plugin action endpoints for missing or absent nonce parameters
• Correlate Referer header anomalies on POST and GET requests to /wp-admin/admin-ajax.php invoking newsletter actions
• Review plugin logs and database tables tracking subscriber status changes for unusual patterns

Monitoring Recommendations

• Enable verbose access logging on the WordPress site and ingest logs into a centralized log analytics platform
• Alert on bulk unsubscription events occurring within short time windows
• Track outbound links from external referrers that terminate at newsletter action URLs

How to Mitigate CVE-2026-1051

Immediate Actions Required

• Update the Newsletter plugin to a version newer than 9.1.0 once a fixed release is available from the plugin vendor
• Audit the WordPress site for unauthorized subscriber status changes since the plugin was installed
• Educate administrators and editors about clicking links from untrusted sources while authenticated to the site

Patch Information

At the time of NVD publication, all versions up to and including 9.1.0 are affected. Site operators should monitor the WordPress plugin repository and the Wordfence Vulnerability Report for patched release information and apply the update through the WordPress admin dashboard or via WP-CLI.

Workarounds

• Deploy a web application firewall (WAF) rule that blocks newsletter action requests lacking a valid same-origin Referer header
• Temporarily disable the Newsletter plugin if active newsletter functionality is not business-critical
• Restrict administrative access to trusted networks to reduce the population of authenticated users exposed to CSRF attempts

# Example WP-CLI command to update the plugin once a fix is released
wp plugin update newsletter

# Verify the installed version after update
wp plugin get newsletter --field=version