CVE-2026-11964 in User Registration & Membership Plugin
Summary
by MITRE • 07/13/2026
The User Registration & Membership WordPress plugin before 5.2.2 does not verify the authenticity of incoming payment-provider webhook notifications before acting on them, allowing unauthenticated attackers to forge a payment-approved event and activate a paid membership subscription without completing a real payment.
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Analysis
by VulDB Data Team • 07/13/2026
The vulnerability exists within the User Registration & Membership WordPress plugin version 5.2.1 and earlier, where the system fails to implement proper authentication checks for incoming webhook notifications from payment providers. This represents a critical security flaw that directly violates the principle of input validation and authentication enforcement as outlined in CWE-862. The plugin processes payment webhook events without verifying their source or authenticity, creating an exploitable condition where malicious actors can craft and send fake webhook messages to trigger membership activation.
This vulnerability allows unauthenticated attackers to manipulate the membership system by forging successful payment notifications from legitimate payment providers such as PayPal, Stripe, or other integrated gateways. The flaw operates at the webhook processing layer where the plugin accepts serialized data without proper cryptographic verification or source authentication mechanisms. Attackers can exploit this by sending specially crafted HTTP requests that mimic legitimate payment provider webhooks, causing the system to automatically grant premium membership access without requiring actual payment processing.
The operational impact of this vulnerability extends beyond simple unauthorized access as it enables attackers to gain premium membership privileges without financial transaction. This creates potential revenue loss for plugin users while simultaneously allowing malicious actors to exploit premium features such as content access restrictions, advanced dashboard functionalities, or other paid service components. The attack vector aligns with ATT&CK technique T1078.004 which covers valid accounts obtained through exploitation of credentials and privilege escalation.
The technical implementation lacks proper webhook signature verification mechanisms that should validate incoming requests against known payment provider authentication standards. According to industry best practices, webhooks should implement cryptographic signatures or shared secrets that authenticate the source of notifications before processing. This vulnerability specifically relates to CWE-347 which addresses insufficient verification of data integrity in security tokens and authentication mechanisms. Organizations using this plugin face significant risk as attackers can repeatedly exploit this flaw without detection, potentially leading to widespread unauthorized membership activation across multiple user accounts.
Mitigation strategies should include immediate plugin updates to version 5.2.2 or later where proper webhook authentication has been implemented. Additionally, administrators should verify that payment provider webhooks are configured with proper security tokens and signature verification mechanisms. Network-level monitoring should be enhanced to detect unusual patterns in membership activation events that could indicate webhook manipulation attempts. The vulnerability demonstrates the critical importance of implementing proper webhook security measures as outlined in OWASP API Security Top 10 category a03, which addresses injection vulnerabilities in API communication channels where unverified inputs can lead to privilege escalation and unauthorized access.