CVE-2026-42331
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.
What this means
- Exposure
- Exploitable remotely over the network, without authentication and with no action from the victim.
- Impact
- An attacker can alter some data. The impact spreads beyond the vulnerable component into other parts of the system.
- Weakness
- A sensitive function is reachable with no authentication at all.
- Likelihood
- Its EPSS score stays low: nothing points to imminent exploitation, which is no reason to leave it unpatched.
What to doFold into the next patch cycle. Start with the instances exposed to the internet.
Read automatically from the CVSS vector, the weakness type (CWE) and the EPSS score. The technical description above remains the one published by NIST.