How severe is CVE-2026-33543?

CVE-2026-33543 has a CVSS 4.0 base score of 9.3, rated critical severity.

Is CVE-2026-33543 being actively exploited?

It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (21st percentile), an estimate of the probability of exploitation in the next 30 days.

How do I fix CVE-2026-33543?

Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its critical severity, prioritise patching exposed systems.

Does CVE-2026-33543 have an EU (EUVD) identifier?

Yes. CVE-2026-33543 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-39096.

When was CVE-2026-33543 published?

CVE-2026-33543 was published on 2026-06-24 and last updated on 2026-06-25.

CVE-2026-33543

CVE-2026-33543 is a critical-severity vulnerability with a CVSS 4.0 base score of 9.3. It is not currently listed as actively exploited by CISA, and its EPSS exploit-prediction score is low. The underlying weakness is classified as CWE-288.

Key facts

Severity: Critical (CVSS 4.0 base score 9.3)
EPSS exploit prediction: 0% (21st percentile)
Actively exploited: Not listed in CISA KEV
EU (EUVD) id: EUVD-2026-39096
Weakness: CWE-288
Published: 2026-06-24
Last modified: 2026-06-25

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.

Frequently asked questions

What is CVE-2026-33543?: 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.
How severe is CVE-2026-33543?: CVE-2026-33543 has a CVSS 4.0 base score of 9.3, rated critical severity.
Is CVE-2026-33543 being actively exploited?: It is not currently listed in CISA's KEV catalog. Its EPSS exploit-prediction score is 0% (21st percentile), an estimate of the probability of exploitation in the next 30 days.
How do I fix CVE-2026-33543?: Review the linked vendor and NVD advisories for patched versions and mitigations, then upgrade or apply the recommended workaround. Given its critical severity, prioritise patching exposed systems.
Does CVE-2026-33543 have an EU (EUVD) identifier?: Yes. CVE-2026-33543 is tracked in the ENISA EU Vulnerability Database (EUVD) as EUVD-2026-39096.
When was CVE-2026-33543 published?: CVE-2026-33543 was published on 2026-06-24 and last updated on 2026-06-25.

References

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