CVE-2026-19804: s2Member <= 260814 - Unauthenticated Remote Code Execution via 'first_name' Parameter in PayPal Proxy Return
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 'firstname' parameter parameter. This is due to insufficient sanitization of the firstname parameter via escrefs(), 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 %%firstname%% 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.
Affected Software
Event History
Frequently Asked Questions
Which sites are exposed to exploitation?
Sites running s2Member version 260814 or earlier are exposed only if an administrator has configured a Signup Tracking Codes template containing the %%first_name%% placeholder. This is a documented, GUI-supported feature rather than an inherently enabled condition.
Does an attacker need an account or user interaction?
No account or user interaction is required. However, the attacker must obtain the site-global proxy verification key, which is exposed in plaintext in the JSON response from any PayPal Checkout AJAX request on the target site.
How can I determine whether my site has the required vulnerable configuration?
Review the configured Signup Tracking Codes templates for use of the %%first_name%% placeholder. Also verify whether the site exposes a PayPal Checkout AJAX response, as the proxy verification key is disclosed in that response.
What is the risk if the exploitation conditions are met?
An unauthenticated attacker can bypass PayPal postback verification and execute code on the server. The reported impact includes compromise of confidentiality, integrity, and availability.