CVE-2026-43928
LowCVSS 2.3Exploitation Probability (EPSS)
Low risk19th percentile - higher than 19% of all known CVEs
Summary
In FOSSBilling versions prior to 0.8.0, the PayPalEmail payment adapter accepts PayPal IPN callbacks and credits the IPN-supplied amount (`mc_gross`) to the client's balance without validating it against the invoice total. Combined with a $0.05 floating-point epsilon tolerance in the invoice credit-payment logic, this allows a client to underpay an invoice by up to $0.04 and still have it marked as fully paid.
Risk Assessment
The organization faces financial losses as clients can intentionally underpay invoices while the system incorrectly marks them as fully paid. This can lead to systematic abuse and difficulties in identifying fraudulent transactions.
Recommendation
Immediately update FOSSBilling to version 0.8.0 or later. Until the update is applied, manually monitor IPN transactions for amounts that do not match invoice totals, and manually review and refund suspicious payments.
Original NVD description (English source)
FOSSBilling is a free, open-source billing and client management system. Prior to version 0.8.0, the PayPalEmail payment adapter accepts PayPal IPN callbacks and credits the IPN-supplied amount (`mc_gross`) to the client's balance without validating it against the invoice total. Combined with a $0.05 floating-point epsilon tolerance in the invoice credit-payment logic, this allows a client to underpay an invoice by up to $0.04 and still have it marked as fully paid. Version 0.8.0 patches the issue. There is no effective workaround without modifying the source code. Merchants using the PayPalEmail adapter should monitor IPN transactions for amounts that do not match their corresponding invoice totals, and manually review and refund suspicious payments.