{"id":"CVE-2026-111056","title":"FOSSBilling: Unauthenticated client account enumeration via guest signup endpoint","summary":"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 signu…","severity":"medium","cvss":6.9,"cvssVector":"CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:L/VI:N/VA:N/SC:N/SI:N/SA:N","cvssSource":"cna","cwe":["CWE-200","CWE-204","CWE-307"],"vendor":"FOSSBilling","product":"FOSSBilling","affected":["FOSSBilling >= 0.1.0, < 0.8.7"],"published":"2026-10-19","updated":"2026-10-19","sourceUpdated":"2026-10-19T16:00:57.576Z","source":"CVEORG","sourceUrl":"https://www.cve.org/CVERecord?id=CVE-2026-111056","references":[{"url":"https://github.com/FOSSBilling/FOSSBilling/security/advisories/GHSA-x4mh-g4pc-wfc5","label":"https://github.com/FOSSBilling/FOSSBilling/security/advisories/GHSA-x4mh-g4pc-wfc5"},{"url":"https://github.com/FOSSBilling/FOSSBilling/pull/4234","label":"https://github.com/FOSSBilling/FOSSBilling/pull/4234"},{"url":"https://github.com/FOSSBilling/FOSSBilling/commit/19f41ff0a45874c7362b7732c8f68db84bc59c55","label":"https://github.com/FOSSBilling/FOSSBilling/commit/19f41ff0a45874c7362b7732c8f68db84bc59c55"},{"url":"https://github.com/FOSSBilling/FOSSBilling/releases/tag/0.8.7","label":"https://github.com/FOSSBilling/FOSSBilling/releases/tag/0.8.7"}],"tags":["cve.org"],"ingestedAt":"2026-10-19T16:32:30.072Z","slug":"CVE-2026-111056","body":"## Overview\n\nFOSSBilling 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.\n\n## Affected\n\n- `FOSSBilling >= 0.1.0, < 0.8.7`\n\n## Remediation\n\nRefer to the linked advisories for vendor-supplied fixes and affected version ranges.","depth":"sunlit","depthScore":38,"depthScoreParts":{"impact":38,"likelihood":0,"exploitation":0,"ransomware":0},"changes":[]}