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Vulnerability record · CVE-2026-33543 · published 24 June 2026

CVE-2026-33543: Authentication bypass via alternate path vulnerability

FOSSBilling is a free, open-source billing and client management system. Versions 0.7.2 and prior expose a guest API endpoint, /api/guest/staff/create, intended for initial administrator bootstrap. Due to a flawed admin-existence check, the endpoint remains usable after an administrator already exists. The flawed guard check uses is_countable() on a value that returns a Model_Admin object or null rather than a countable type, causing the expression to always evaluate as true and bypass the intended protection. As a result, an attacker can reach the unprotected endpoint to create a new administrator account and immediately authenticate, gaining a fully privileged admin session even when an admin already exists. This issue has been fixed in version 0.8.0.

9.3 CVSS 4.0 Critical EPSS 0.45% · top 63.6% CWE-288 · Authentication bypass via alternate pathCWE-306 · Missing authentication for critical function Deferred
9.3CVSS 4.0 base score
0.45%EPSS exploitation probability, 30 days
NoNot in CISA KEV
0Affected product versions listed by NVD
2References
25 Jun 2026Last modified by NVD

Description

FOSSBilling is a free, open-source billing and client management system. Versions 0.7.2 and prior expose a guest API endpoint, /api/guest/staff/create, intended for initial administrator bootstrap. Due to a flawed admin-existence check, the endpoint remains usable after an administrator already exists. The flawed guard check uses is_countable() on a value that returns a Model_Admin object or null rather than a countable type, causing the expression to always evaluate as true and bypass the intended protection. As a result, an attacker can reach the unprotected endpoint to create a new administrator account and immediately authenticate, gaining a fully privileged admin session even when an admin already exists. This issue has been fixed in version 0.8.0.

CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:

References

LinkTags
https://github.com/FOSSBilling/FOSSBilling/releases/tag/0.8.0
https://github.com/FOSSBilling/FOSSBilling/security/advisories/GHSA-28mh-j262-q49w

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Source: NIST National Vulnerability Database (record CVE-2026-33543), CISA KEV, FIRST EPSS (scores of 2026-09-26). This page is refreshed as NVD updates the record.