CVE-2026-42331 FOSSBilling missing authorization in guest Invoice API endpoints
Unauthenticated attackers can modify payment gateways on unpaid invoices if invoice hashes are exposed, requiring the accessible-from-hash setting to be enabled.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- None listed
What is CVE-2026-42331?
CVE-2026-42331 is a high-severity missing authorization vulnerability in FOSSBilling, published on 6 Jul 2026. An attacker can exploit it over the internet without logging in, 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 Guest API invoice/update endpoint is missing an authorization check present in other invoice-related endpoints, allowing an unauthenticated user with knowledge of an invoice hash to modify the payment gateway associated with an unpaid invoice. An attacker who obtains an invoice hash, which may leak through shared URLs, referrer headers, or email links, can change the `gateway_id` on an unpaid invoice to any payment gateway configured in the system. This does not allow redirecting payments to an arbitrary external endpoint, as the gateway must already be installed and configured by an administrator. The practical impact is further limited by the `invoice_accessible_from_hash` system setting. Version 0.8.0 contains a patch. No known workarounds are available.
Which versions are affected by CVE-2026-42331?
How do I fix CVE-2026-42331?
No fix has been published for CVE-2026-42331 yet. Limit exposure of the affected software until one is available.
Upgrade, and check permissions on every request on the server, not only in the interface. More about Missing authorization.
Is CVE-2026-42331 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-42331 exists.
Sources
Also known as GHSA-8755-w77f-3g7j.