clavaque s2Member Plugin prior 260814 on WordPress esc_refs first_name os command injection

Summaryinfo

A vulnerability described as critical has been identified in clavaque s2Member Plugin. This affects the function esc_refs. Such manipulation of the argument first_name leads to os command injection. This vulnerability is uniquely identified as CVE-2026-19804. The attack can be launched remotely. No exploit exists. Upgrading the affected component is recommended.

Detailsinfo

A vulnerability, which was classified as critical, has been found in clavaque s2Member Plugin. Affected by this issue is the function esc_refs. The manipulation of the argument first_name with an unknown input leads to a os command injection vulnerability. Using CWE to declare the problem leads to CWE-78. The product constructs all or part of an OS command using externally-influenced input from an upstream component, but it does not neutralize or incorrectly neutralizes special elements that could modify the intended OS command when it is sent to a downstream component. Impacted is confidentiality, integrity, and availability. CVE summarizes:

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.

The advisory is available at wordfence.com. This vulnerability is handled as CVE-2026-19804 since 08/13/2026. The exploitation is known to be easy. The attack may be launched remotely. No form of authentication is required for exploitation. Technical details are known, but there is no available exploit. This vulnerability is assigned to T1202 by the MITRE ATT&CK project.

Upgrading to version 260814 eliminates this vulnerability. Applying the patch 260814 is able to eliminate this problem. The best possible mitigation is suggested to be upgrading to the latest version.

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Productinfo

Type

• WordPress Plugin

Vendor

• clavaque

Name

• s2Member Plugin

CPE 2.3info

• 🔒

CPE 2.2info

• 🔒

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