Executive brief
The Paid Member Subscriptions WordPress plugin fails to validate that payment amounts and currency codes received from PayPal match the membership plan being purchased. An unauthenticated attacker can exploit this to pay a lower amount than required and still gain access to paid membership features, resulting in direct revenue loss and unauthorized service access.
Technical details
The plugin contains an access control vulnerability (CWE-284) in its PayPal payment verification logic. When processing payment completion, it does not compare the amount and currency reported by the PayPal webhook against the original pending payment details. An unauthenticated attacker can intercept or manipulate the payment callback to specify an arbitrary lower amount and currency mismatch, which the plugin accepts without validation. This allows the attacker to obtain paid membership access without paying the correct fee. The vulnerability was fixed in version 3.0.9.
Affected products
- Paid Member Subscriptions Paid Member Subscriptions before 3.0.9
Timeline
- 2026-09-15: disclosed
- 2026-09-17: patched: Fixed in version 3.0.9