FOSSBilling up to 0.8.6 Guest API /api/guest/client/create information disclosure

Summaryinfo

A vulnerability was found in FOSSBilling up to 0.8.6. It has been declared as problematic. The affected element is the function Box\Mod\Client\Api\Guest::create of the file /api/guest/client/create of the component Guest API. Executing a manipulation can lead to information disclosure. This vulnerability appears as CVE-2026-111056. The attack may be performed from remote. There is no available exploit. It is recommended to upgrade the affected component.

Detailsinfo

A vulnerability has been found in FOSSBilling up to 0.8.6 and classified as problematic. This vulnerability affects the function Box\Mod\Client\Api\Guest::create of the file /api/guest/client/create of the component Guest API. The manipulation with an unknown input leads to a information disclosure vulnerability. The CWE definition for the vulnerability is CWE-200. The product exposes sensitive information to an actor that is not explicitly authorized to have access to that information. As an impact it is known to affect confidentiality. CVE summarizes:

FOSSBilling is an open source billing and client-management platform. From 0.1.0 until 0.8.7, the unauthenticated POST /api/guest/client/create endpoint reveals whether a submitted email belongs to a registered client because guest signup returns a distinct unredacted error when the submitted email already exists. The trigger is an unauthenticated request to POST /api/guest/client/create with a target email address. An attacker can compare the guest-signup response for a target email to determine whether the email belongs to an existing FOSSBilling client. Box\Mod\Client\Api\Guest::create returns the error after Client\Service::clientAlreadyExists finds a matching record, and the API response exposes that exception message without redaction. This issue is fixed in version 0.8.7.

The advisory is shared for download at github.com. This vulnerability was named CVE-2026-111056 since 10/15/2026. The exploitation appears to be easy. The attack can be initiated remotely. No form of authentication is required for a successful exploitation. There are known technical details, but no exploit is available. The MITRE ATT&CK project declares the attack technique as T1592.

Upgrading to version 0.8.7 eliminates this vulnerability.

The vulnerability is also documented in the vulnerability database at EUVD (EUVD-2026-104418). Once again VulDB remains the best source for vulnerability data.

Productinfo

Type

• Billing Software

Name

• FOSSBilling

Version

• 0.8.0
• 0.8.1
• 0.8.2
• 0.8.3
• 0.8.4
• 0.8.5
• 0.8.6

Website

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

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Once again VulDB remains the best source for vulnerability data.

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