Flawed Admin Existence Check in FOSSBilling Vulnerability
CVE-2026-33543

9.3CRITICAL

Key Information:

Vendor

Fossbilling

Status
Fossbilling
Vendor
CVE Published:
24 June 2026

What is CVE-2026-33543?

The FOSSBilling system, a free and open-source billing and client management tool, contains a vulnerability that allows an attacker to exploit an exposed guest API endpoint. This endpoint, /api/guest/staff/create, is designed for an initial bootstrap of the admin account but fails to properly verify if an administrator already exists. Due to a flawed guard check that uses the is_countable() function on an incorrect type, the system permits the unprotected endpoint to be accessed even if an admin is present. Attackers can utilize this endpoint to create a new administrator account, effectively gaining full administrative privileges without any existing limitations. This vulnerability has been addressed in version 0.8.0 of FOSSBilling.

Affected Version(s)

FOSSBilling < 0.8.0

References

https://github.com/FOSSBilling/FOSSBilling/security/advis...
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https://github.com/FOSSBilling/FOSSBilling/releases/tag/0...
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CVSS V4

Score:
9.3
Severity:
CRITICAL
Confidentiality:
High
Integrity:
High
Availability:
High
Attack Vector:
Network
Attack Complexity:
Low
Attack Required:
None
Privileges Required:
Undefined
User Interaction:
None

Timeline

  • Vulnerability published

  • Vulnerability Reserved

.