# CVE-2026-33543: FOSSBilling authentication bypass in guest staff creation API

Source: https://junglewise.ai/threats/cve-2026-33543-fossbilling-authentication-bypass-in-guest-staff-creation-api  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-06-24. Updated: 2026-06-24  
License: CC BY 4.0 with a link back

CVE-2026-33543 · Severity: info · CVSS 9.3 · Published 2026-06-24

FOSSBilling, an open-source billing and client management platform, contains a critical security flaw that allows anyone to create a new administrator account without any existing credentials. By accessing a specific web address intended only for initial setup, an attacker can bypass security checks and gain full control over the system. This could lead to the theft of customer data, financial records, and complete disruption of the billing service.

Technologies: [FOSSBilling](https://junglewise.ai/threats/technologies/fossbilling). Vendors: [FOSSBilling](https://junglewise.ai/threats/vendors/fossbilling).

## Quick answers

**Is CVE-2026-33543 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-33543 being exploited in the wild.

**How severe is CVE-2026-33543?** Informational severity, with a CVSS score of 9.3, published 24 June 2026.

**Which products and versions are affected?** FOSSBilling <= 0.7.2.

**Is there a fix for CVE-2026-33543?** A patch was published on 2026-05-28: Version 0.8.0 released Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-33543 attacked?** It is attacked over the network, in a web application.

**Am I affected by CVE-2026-33543?** Check whether you run FOSSBilling at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## Technical details

An authentication bypass exists in the `/api/guest/staff/create` endpoint of FOSSBilling due to a flawed logic check in `src/modules/Staff/Api/Guest.php`. The endpoint is intended for initial bootstrap but fails to properly verify if an administrator already exists. The check uses `is_countable()` on a `Model_Admin` object or `null` returned by the database; since these types are not countable, the expression `!is_countable(...)` always evaluates to true. This allows an unauthenticated remote attacker to trigger the `createAdmin()` and `login()` functions, resulting in a fully privileged administrative session. The vulnerability is patched in version 0.8.0.

## Affected products

- FOSSBilling FOSSBilling <= 0.7.2

## Timeline

- 2026-05-28: patched: Version 0.8.0 released
- 2026-06-20: advisory: GitHub Security Advisory published
- 2026-06-24: disclosed: CVE-2026-33543 published to NVD

## References

- [https://github.com/FOSSBilling/FOSSBilling/releases/tag/0.8.0](https://github.com/FOSSBilling/FOSSBilling/releases/tag/0.8.0)
- [https://github.com/FOSSBilling/FOSSBilling/security/advisories/GHSA-28mh-j262-q49w](https://github.com/FOSSBilling/FOSSBilling/security/advisories/GHSA-28mh-j262-q49w)

## Related threats

- [FOSSBilling stored XSS in support ticket notes](https://junglewise.ai/threats/cve-2026-111048-fossbilling-is-an-open-source-billing-and-client-management)
- [FOSSBilling CSRF vulnerability in staff guest login endpoint](https://junglewise.ai/threats/cve-2026-112374-fossbilling-before-0-8-9-contains-a-cross-site-request-forgery)
- [FOSSBilling email enumeration via guest signup endpoint](https://junglewise.ai/threats/cve-2026-111056-fossbilling-is-an-open-source-billing-and-client-management)
- [FOSSBilling path traversal in template_exists endpoint](https://junglewise.ai/threats/cve-2026-111053-fossbilling-is-an-open-source-billing-and-client-management)
- [FOSSBilling authorization bypass in extension configuration management](https://junglewise.ai/threats/cve-2026-111046-fossbilling-is-an-open-source-billing-and-client-management)