The Simple Membership WordPress plugin before 4.8.3 does not avoid transmitting a newly registered member's plaintext password in a URL query string when an optional auto-login-after-registration feature is enabled, exposing the credential in browser history and in web server, proxy, and CDN access logs to anyone able to read them.

The Simple Membership plugin for WordPress is vulnerable to unauthorized modification of data and sensitive information disclosure in versions up to, and including, 4.8.3 via the resend-activation and email-activation endpoints. The endpoints are dispatched from SwpmInitTimeTasks::checkanddoemailactivation() on frontend init with no authentication, nonce, capability, or ownership check, and the recipient address used by SwpmRegistration::sendregemail() is taken from an attacker-controlled $POST['email'] parameter (overriding the member's registered address). This makes it possible for unauthenticated attackers to redirect an arbitrary pending member's activation email — and the follow-up 'registration complete' email containing the member's username and plaintext password — to an attacker-chosen address, and to then activate that member's account without their consent.

The Simple Membership plugin for WordPress is vulnerable to authorization bypass in all versions up to, and including, 4.7.5. This is due to the plugin not properly verifying that a user is authorized to perform an action. This makes it possible for unauthenticated attackers to deactivate arbitrary member accounts by forging a charge.refunded webhook event containing a victim's subscription ID, setting the target member's accountstate to 'inactive' and triggering cancellation hooks, transaction-record status changes, and cancellation notification emails. This vulnerability is exploitable only on installations where no Stripe webhook signing secret has been configured, which is the default out-of-the-box state; sites that have configured the stripe-webhook-signing-secret option are routed to the properly verified HMAC path and are not affected.

The Simple Membership plugin for WordPress is vulnerable to Sensitive Information Exposure in all versions up to, and including, 4.5.5 via the WordPress core search feature. This makes it possible for unauthenticated attackers to extract sensitive data from posts that have been restricted to higher-level roles such as administrator.

The Simple Membership plugin for WordPress is vulnerable to Stored Cross-Site Scripting via the plugin's 'swpmpaypalsubscriptioncancellink' shortcode in all versions up to, and including, 4.4.5 due to insufficient input sanitization and output escaping on user supplied attributes. This makes it possible for authenticated attackers, with contributor-level access and above, to inject arbitrary web scripts in pages that will execute whenever a user accesses an injected page.

The Simple Membership plugin for WordPress is vulnerable to Stored Cross-Site Scripting via the plugin's 'swpmpaypalsubscriptioncancellink' shortcode in all versions up to, and including, 4.4.3 due to insufficient input sanitization and output escaping on user supplied attributes. This makes it possible for authenticated attackers, with contributor-level access and above, to inject arbitrary web scripts in pages that will execute whenever a user accesses an injected page.