Is CVE-2026-42331 exploited in the wild?

No. Junglewise Threat Intelligence has no report of CVE-2026-42331 being exploited in the wild.

How severe is CVE-2026-42331?

Informational severity, with a CVSS score of 7.7, published 6 July 2026.

Is there a fix for CVE-2026-42331?

No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.

How is CVE-2026-42331 attacked?

It is attacked over the network, in a web application.

Am I affected by CVE-2026-42331?

Check whether you run FOSSBilling at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

CVE-2026-42331: FOSSBilling missing authorization in Guest API invoice endpoints

CVE-2026-42331 · Severity: info · CVSS 7.7 · Published 2026-07-06

FOSSBilling is an open-source platform used by businesses to manage client billing and automated invoicing. A security flaw in the system's guest interface allows unauthorized individuals to modify unpaid invoices if they obtain a specific web link or invoice ID. While an attacker cannot redirect payments to their own personal bank account unless they have already compromised the system's settings, they can disrupt business operations by changing which approved payment method is used for a transaction.

Technologies: FOSSBilling. Vendors: FOSSBilling.

Quick answers

Is CVE-2026-42331 exploited in the wild?: No. Junglewise Threat Intelligence has no report of CVE-2026-42331 being exploited in the wild.
How severe is CVE-2026-42331?: Informational severity, with a CVSS score of 7.7, published 6 July 2026.
Which products and versions are affected?: FOSSBilling < 0.8.0.
Is there a fix for CVE-2026-42331?: No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.
How is CVE-2026-42331 attacked?: It is attacked over the network, in a web application.
Am I affected by CVE-2026-42331?: Check whether you run FOSSBilling at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

Technical details

The vulnerability is caused by a missing authorization check (`checkInvoiceAuth()`) in the `invoice/update` and `invoice/payment` endpoints within the Guest API (`src/modules/Invoice/Api/Guest.php`). An unauthenticated attacker who obtains a valid invoice hash—potentially leaked via referrer headers, shared URLs, or emails—can send a POST request to modify the `gateway_id` of an unpaid invoice. Additionally, the `payment` endpoint can be used to access payment adapter HTML output, potentially exposing sensitive transaction details. The exploit is limited to gateways already configured in the system by an administrator. The issue is addressed in version 0.8.0.

Affected products

FOSSBilling FOSSBilling < 0.8.0

Timeline

2026-06-20: advisory: GitHub security advisory published
2026-07-06: disclosed: NVD publication date

References

https://github.com/FOSSBilling/FOSSBilling/security/advisories/GHSA-8755-w77f-3g7j

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