CVE-2026-27604: FOSSBilling: Improper API Role Validation (system) Enables Unauthenticated Access to Privileged Admin Functions

Is it exploited?

Reported, not confirmed by CISA. VulnCheck KEV lists it as exploited in the wild. CISA has not added it to its Known Exploited Vulnerabilities catalog as of 10 Nov 2026.

VulnCheck KEV lists it since 10 Nov 2026. VulnCheck's own honeypots also recorded exploitation attempts.

How likely is exploitation in the next 30 days?

1.3%

EPSS score, percentile 70.1 of all scored records. A probability estimated by FIRST, not a report of exploitation.

How severe?

10.0 Critical

CVSS v4.0 base score, given by the CNA

What should I do?

CISA has set no required action, because the vulnerability is not in KEV.

No patch or vendor advisory is listed in the CVE record. Check FOSSBilling's advisories.

Which versions are affected?

Affected

• >= 0.5.4, < 0.8.0

Versions by product

Source: CISA KEV 2026.11.10, as of 10 Nov 2026; VulnCheck KEV, as of 12 Nov 2026; FIRST EPSS, as of 12 Nov 2026; CVE List, as of 12 Nov 2026. About the data.

Description

FOSSBilling: Improper API Role Validation (system) Enables Unauthenticated Access to Privileged Admin Functions

FOSSBilling is a free, open-source billing and client management system. Starting in version 0.5.4 and prior to version 0.8.0, an authorization bypass in the API role handling allows unauthenticated access to privileged `/api/system/*` endpoints. Because `system` resolves to the cron admin identity, attackers can invoke admin API methods without valid credentials, session, or CSRF token. Version 0.8.0 patches the issue. Some workarounds are available. Block external access to `/api/system/*` at reverse proxy/WAF, restrict API access by trusted source IPs only (`api.allowed_ips`), rotate all admin/client API tokens immediately, invalidate active sessions and reset high-privilege credentials, and/or review API request logs for suspicious `/api/system/` access and treat as potential incident.

Source: CVE List, as of 12 Nov 2026. About the data.

What to do

Advisories and patches

No patch, vendor advisory or mitigation is listed in the CVE record. Check FOSSBilling's own security advisories for a fix, and compare your version with the affected versions below.

This summary is based on the CVE record as of 12 Nov 2026. Check the vendor's advisory before you act: affected versions and fixes can change.

Affected products and versions

Source: CVE List, as of 12 Nov 2026. About the data.

Timeline