s2Member <= 260814 - Unauthenticated Remote Code Execution via 'first_name' Parameter in PayPal Proxy Return

Summary

The s2Member – Excellent for All Kinds of Memberships, Content Restriction Paywalls & Member Access Subscriptions plugin for WordPress is vulnerable to Remote Code Execution in all versions up to, and including, 260814 via the 'first_name' parameter parameter. This is due to insufficient sanitization of the first_name parameter via esc_refs(), which strips only regex backreferences and not PHP tags, before substitution into the eval'd Signup Tracking Codes template, combined with disclosure of the site-global proxy verification key that allows PayPal postback verification to be bypassed. This makes it possible for unauthenticated attackers to execute code on the server. Successful exploitation requires that the site administrator has configured a Signup Tracking Codes template containing the %%first_name%% placeholder (a documented, GUI-supported feature) and that the attacker has obtained the site-global proxy verification key, which is exposed in plaintext in the JSON response of any PayPal Checkout AJAX request on the target site.

Timeline

1. Sep 25, 2026, 7:40 AM UTCCVE published
2. Sep 25, 2026, 12:49 PM UTCCISA SSVC assessment

   Exploitation: none · Automatable: no · Technical impact: total

3. Sep 25, 2026, 1:00 PM UTCRecord last updated

Affected versions

• clavaque s2Member – Excellent for All Kinds of Memberships, Content Restriction Paywalls & Member Access Subscriptions

  through 260814

References 10