FOSSBilling up to 0.5.5 Guest API gateway_id improper authorization

Summaryinfo

A vulnerability categorized as problematic has been discovered in FOSSBilling. This affects an unknown function of the component Guest API. Such manipulation of the argument gateway_id leads to improper authorization. This vulnerability is listed as CVE-2026-42331. The attack may be performed from remote. There is no available exploit.

Detailsinfo

A vulnerability was found in FOSSBilling and classified as problematic. Affected by this issue is an unknown functionality of the component Guest API. The manipulation of the argument gateway_id with an unknown input leads to a improper authorization vulnerability. Using CWE to declare the problem leads to CWE-285. The product does not perform or incorrectly performs an authorization check when an actor attempts to access a resource or perform an action. Impacted is integrity. CVE summarizes:

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.

The advisory is available at github.com. This vulnerability is handled as CVE-2026-42331 since 04/26/2026. The exploitation is known to be easy. The attack may be launched remotely. No form of authentication is required for exploitation. Technical details are known, but there is no available exploit. This vulnerability is assigned to T1548.002 by the MITRE ATT&CK project.

Upgrading to version 0.8.0 eliminates this vulnerability.

The vulnerability is also documented in the vulnerability database at EUVD (EUVD-2026-41947). If you want to get best quality of vulnerability data, you may have to visit VulDB.

Productinfo

Type

• Billing Software

Name

• FOSSBilling

Version

• 0.5.0
• 0.5.1
• 0.5.3
• 0.5.4
• 0.5.5

Website

• Product: https://github.com/FOSSBilling/FOSSBilling/

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If you want to get best quality of vulnerability data, you may have to visit VulDB.

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