---
cve: "CVE-2026-33543"
severity: "CRITICAL"
cvss: 9.3
epss: "29%"
vendor: "fossbilling"
kev: false
exploited: false
published: "2026-06-24 21:01:16"
tags: [cve, security, critical]
source: tsecurity.de CVE-Dossier
exported: "2026-09-18T01:54:35+02:00"
---

# CVE-2026-33543

> 9.3 CRITICAL · 🧪 PoC

## Beschreibung

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-Vektor

```
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
```

| Metrik | Wert | Bewertung |
|---|---|---|
| AV Angriffsvektor | Netzwerk | bad |
| AC Komplexität | Gering | bad |
| PR Privilegien | Keine | bad |
| UI Interaktion | Keine | bad |

## Patch verfügbar (OSV)

- 3bd35f5b2921d8a26a403142ae0408f95e6463cc (Commit)

## Referenzen

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

---
_Exportiert aus dem [tsecurity.de CVE-Dossier](https://tsecurity.de/cve?cve=CVE-2026-33543) · Datenquellen: EUVD (ENISA), NVD, OSV, CISA KEV, FIRST EPSS, Exploit-DB, BSI BITS_