CVE-2026-33543 FOSSBilling: Authentication bypass allows unauthenticated administrator creation
An authentication bypass in FOSSBilling allows attackers to create administrator accounts via a guest API endpoint, gaining full administrative privileges.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- None listed
What is CVE-2026-33543?
CVE-2026-33543 is a critical authentication bypass vulnerability in FOSSBilling, published on 24 Jun 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Official 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.
Which versions are affected by CVE-2026-33543?
How do I fix CVE-2026-33543?
No fix has been published for CVE-2026-33543 yet. Limit exposure of the affected software until one is available.
Upgrade, and rotate credentials and sessions that may have been exposed. More about Authentication bypass.
Is CVE-2026-33543 being exploited?
There is no known exploitation of CVE-2026-33543 in the wild and no public exploit code.
Sources
Also known as GHSA-28mh-j262-q49w.