| Title | FOSSBilling <= 0.8.6 Authentication Bypass Issues |
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| Description | The unauthenticated guest signup endpoint (POST /api/guest/client/create) discloses whether a given email address already belongs to a registered client. Guest::create() throws the error "This email address is already registered." when Client\Service::clientAlreadyExists() finds a matching row, and returns a new client ID otherwise. Because the API layer passes exception messages straight through to the JSON response with no redaction, this is a clean existence oracle for any FOSSBilling deployment's customer email list. |
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| Source | ⚠️ https://github.com/FOSSBilling/FOSSBilling/security/advisories/GHSA-x4mh-g4pc-wfc5 |
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| User | mikannse (UID 100854) |
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| Submission | 10/08/2026 03:52 (14 days ago) |
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| Moderation | 10/21/2026 12:48 (13 days later) |
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| Status | Duplicate |
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| VulDB entry | 422428 [FOSSBilling up to 0.8.6 Guest API /api/guest/client/create information disclosure] |
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| Points | 0 |
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