CVE-2026-43928 FOSSBilling: Payment amount not validated in PayPalEmail adapter allows invoice underpayment
Attackers can underpay invoices by exploiting missing validation in the PayPalEmail adapter, leading to financial loss for merchants.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- None listed
What is CVE-2026-43928?
CVE-2026-43928 is a low-severity vulnerability in FOSSBilling, published on 6 Jul 2026. Any signed-in user can exploit it over the network, with no action from the victim.
Official description
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.
Which versions are affected by CVE-2026-43928?
How do I fix CVE-2026-43928?
No fix has been published for CVE-2026-43928 yet. Limit exposure of the affected software until one is available.
Is CVE-2026-43928 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-43928 exists.
Sources
Also known as GHSA-xjc6-g382-h942.