Live Exposure Defense: From CVE to Confirmed Exposure in 12 Hours – See more

Back
New CVE Detected

CVE-2026-33543 – Authentication Bypass – FOSSBilling ≤ 0.7.2

Be the first to know when new zero-days emerge:

Subscribe to Email Alerts
Subscribe to RSS Feed

Summary

CVE-2026-33543 is a critical authentication bypass vulnerability in FOSSBilling, a free open-source billing and client management system, affecting all versions up to and including 0.7.2. A logic flaw in a guest API endpoint originally intended for first-time administrator bootstrapping allows an unauthenticated remote attacker to create a new administrator account and immediately obtain a fully privileged admin session on any exposed instance. This vulnerability carries a CVSS 4.0 score of 9.3 (Critical).

Technical details

  • Root cause: The admin-existence guard in the /api/guest/staff/create endpoint calls is_countable() on the return value of Box_Database::findOne(), which returns a Model_Admin object or null — neither of which is a countable type. Because is_countable() returns false for both types and the check applies a negation operator, the expression permanently evaluates to true, bypassing the intended protection regardless of whether an administrator already exists on the system.
  • Affected components: src/modules/Staff/Api/Guest.php (create() method) and src/modules/Staff/Service.php (createAdmin() and login() methods).
  • Trigger conditions: A single unauthenticated HTTP POST request to /api/guest/staff/create on any exposed instance running version 0.7.2 or earlier. No credentials, session tokens, or prior access of any kind are required.
  • Attack vector: Remotely exploitable over the network with no attack complexity, no prerequisites, and no user interaction (CVSS 4.0: AV:N, AC:L, AT:N, PR:N, UI:N).
  • Impact: An attacker can instantly register a new administrator account and authenticate into the full admin panel and API, resulting in complete administrative compromise — including unrestricted access to customer data, financial records, hosted service configurations, and all billing operations.

Affected software

  • FOSSBilling versions 0.1.0 through 0.7.2 (all versions prior to 0.8.0)

Severity

CVSS 4.0 Base Score: 9.3 (Critical)
Vector String: 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

  • CWE-288: Authentication Bypass Using an Alternate Path or Channel
  • CWE-306: Missing Authentication for Critical Function

Mitigation and recommended actions

  • Immediate: Upgrade to FOSSBilling 0.8.0 (released May 28, 2026), which resolves this vulnerability.
  • If immediate patching is not possible: Block external access to the /api/guest/staff/create endpoint at the reverse proxy or WAF level, and restrict API access to trusted source IPs only. Additionally, audit all administrator accounts on the affected instance for any unauthorized entries and revoke them immediately.

IONIX Status

The IONIX research team is tracking ongoing exploitation attempts and recommends immediate patching. Potentially affected assets are outlined in this post.

References

Are you exposed?

Get a free report of your organization’s exposure to this CVE and threat

  • Mapping of all Assets with this Technology
  • Identification of potentially exposed assets to this CVE
  • Confirmation of verified exploitable assets
Get Exposure Report

How IONIX’s External Exposure Management Platform Detects and Validates
Zero-Days to Shrink MTTR

1

Map your entire attack surface (continously)

IONIX uses multi-factor discovery methods, including DNS analysis, certificate mapping, metadata inspection, and more, to automatically map every internet-facing asset across your environment. This includes cloud instances, third-party platforms, shadow IT, and even forgotten infrastructure that traditional tools miss.

2

Monitor for new CVEs

Dozens of threat intel feeds using agentic technology are continuously analyzed to detect the appearance of proof-of-concept code, exploit kits, and indicators of active targeting. IONIX goes further by applying AI to proactively evaluate whether emerging vulnerabilities are likely to be exploited, even before PoCs go public.

3

Identify Potential External Exposures

Not all CVEs matter. IONIX filters vulnerabilities by asking attacker-centric questions: Can it be reached from the internet? Does it require authentication? Is it being exploited in the wild? This dramatically reduces noise and focuses teams on threats that can actually be weaponized.

4

Create Safe, Scalable Exploit Validations

IONIX transforms real-world PoCs into safe, non-intrusive test payloads that can be run in production environments without disruption. These simulations are precisely targeted to the systems that are vulnerable, ensuring rapid validation without unnecessary load.

5

Execute Exploit Validations

By combining context about software stack, versioning, exposure status, and reachability, IONIX ensures that only the right payloads are executed against the right assets, maximizing efficiency and minimizing risk.

6

Drive Fast and Actionable Remediation

Results are routed through integrations with ticketing, SOAR, and SIEM tools. Issues are written in plain language, bundled into remediation clusters, and prioritized based on asset criticality, exploitability, and blast radius. This shortens mean time to remediation (MTTR) and empowers teams to act with confidence.

Are you exposed?

Get a free report of your organization’s exposure to this CVE and threat

  • Mapping of all Assets with this Technology
  • Identification of potentially exposed assets to this CVE
  • Confirmation of verified exploitable assets
Get Exposure Report
Close

Subscribe to Threat Center RSS

Copy/paste the link below into your preferred RSS reader or follow these instructions to subscribe to Slack alerts.

Open RSS feedSlack setup instructions

Close

Get Real-Time CVE Alerts to Your Email

Be the first to know when new zero-days emerge