CVE-2026-33543
FOSSBilling: Authentication bypass allows unauthenticated administrator creation
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.
INFO
Published Date :
June 24, 2026, 9:01 p.m.
Last Modified :
June 24, 2026, 9:01 p.m.
Remotely Exploit :
Yes !
Source :
GitHub_M
Affected Products
The following products are affected by CVE-2026-33543
vulnerability.
Even if cvefeed.io is aware of the exact versions of the
products
that
are
affected, the information is not represented in the table below.
No affected product recoded yet
CVSS Scores
| Score | Version | Severity | Vector | Exploitability Score | Impact Score | Source |
|---|---|---|---|---|---|---|
| CVSS 4.0 | CRITICAL | [email protected] |
Solution
- Update FOSSBilling to version 0.8.0 or later.
- Verify the guest API endpoint is no longer accessible.
- Ensure administrator creation is restricted.
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CVE-2026-33543 vulnerability anywhere in the article.