CVE-2026-111056
FOSSBilling: Unauthenticated client account enumeration via guest signup endpoint
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.
| CWE | CWE-200 CWE-204 CWE-307 |
| Vendor | fossbilling |
| Product | fossbilling |
| Published | Oct 19, 2026 |
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