CVE-2026-90922 in Paid Membership Subscriptions Plugin
Summary
by MITRE • 09/17/2026
The Paid Membership Subscriptions WordPress plugin before 3.0.9 does not verify that the amount and currency reported by the payment provider match the pending payment before completing it, allowing unauthenticated users to obtain a paid membership by paying an arbitrary lower amount.
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Analysis
by VulDB Data Team • 09/17/2026
The vulnerability identified in the Paid Membership Subscriptions WordPress plugin prior to version 3.0.9 represents a critical business logic flaw rooted in insufficient validation of financial transaction data during the checkout process. This issue specifically affects the integration between the payment gateway and the subscription management system, where the application fails to perform integrity checks on the monetary values returned by external payment providers. In secure e-commerce architectures, it is imperative that the server-side state regarding a pending order's expected cost and currency type be strictly compared against the actual data received from the third-party payment processor upon callback or webhook completion. The absence of this verification step creates a significant gap in the application's security posture, allowing for potential financial fraud through manipulation of transaction parameters.
From a technical perspective, the flaw allows unauthenticated attackers to exploit the lack of server-side validation by intercepting and modifying the response data sent from the payment gateway back to the WordPress site. By altering fields such as amount or currency code in transit or via direct API calls if exposed, an attacker can submit a request indicating that a lower fee has been paid for a subscription tier that requires a higher standard price. Since the plugin proceeds to activate the membership privileges based solely on the payment provider's confirmation without cross-referencing it against its own internal records of what was originally requested and quoted, the system erroneously grants access. This mechanism bypasses authentication requirements entirely because the exploitation relies on manipulating the post-payment state transition rather than breaking into user accounts or exploiting input validation flaws in login forms.
The operational impact of this vulnerability is severe for any organization relying on paid subscriptions through this plugin to generate revenue. Attackers can obtain premium membership benefits, such as access to exclusive content, services, or features, without paying the required fees. This results in direct financial loss proportional to the number of successful exploits and undermines the integrity of the business model. Furthermore, if the vulnerability is automated at scale, it could lead to significant revenue erosion and potential abuse of resources that are intended only for paying customers. The lack of authentication requirement means that any internet user with basic knowledge of web request manipulation can attempt this attack, increasing the likelihood of successful exploitation in unpatched environments.
This type of flaw aligns closely with CWE-840, which describes Business Logic Errors where the application performs an action without proper validation or authorization checks relevant to business rules. Additionally, it relates to CWE-209, as the generation of error messages or status updates might inadvertently reveal information about the system's state if not handled carefully during exploitation attempts. In terms of offensive security frameworks like MITRE ATT&CK, this vulnerability facilitates techniques associated with T1583, specifically Acquire Infrastructure for Financial Gain, by allowing attackers to establish a foothold in paid services without cost. It also touches upon aspects of privilege escalation, albeit at the application logic level rather than system permissions, effectively granting unauthorized access rights through financial manipulation.
To mitigate this vulnerability, immediate action is required to upgrade the Paid Membership Subscriptions plugin to version 3.0.9 or later, where these validation checks have presumably been implemented by the developers. In addition to updating software, administrators should ensure that their payment gateway integrations are configured to use secure callbacks and webhooks with signature verification if supported by the provider. Implementing server-side reconciliation processes is crucial; this involves maintaining a local record of pending transactions with their expected amounts and currencies, which must be strictly compared against the data received from the payment processor before any membership status changes or access rights are granted. Regular security audits focusing on financial transaction flows can help identify similar logic flaws in other plugins or custom code within the WordPress ecosystem to prevent future occurrences of this class of business logic vulnerabilities.