TI-2026-21990 Aliases CVE-2026-27604

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

MEDIUM 51CWE-200Published 2026-06-23 · Updated 2026-06-23

Key facts

Attack vector: Network
Privileges required: None
User interaction: None
Attack complexity: Low
Attack requirements: None
Impact type: Information disclosure, Security bypass
Confidentiality · integrity · availability: High · High · High
Fix status: Fixed

Attack profile from CVSS 4.0 · CNA. Fix status from CNA. Impact type from CWE-200 and CWE-306.

Summary

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.

Why it matters now

Exploitation None reported CISA SSVC · not in CISA KEV

EPSS 0.01264 69th percentileScored 2026-11-07

Fix Fixed FOSSBilling (FOSSBilling): 0.8.0

SSVC decision points

CISA ADP · SSVC 2.0.3

Exploitation: None
Automatable: Yes
Technical impact: Total

The decision (Track, Attend, Act) also depends on your mission and well-being impact; see CISA's SSVC guide.

Affected products

Vendor	Product	Affected versions	Fixed in	Status	Source
FOSSBilling	FOSSBilling	0.5.4 to before 0.8.0	0.8.0	Patch available	CNA

FOSSBilling VendorFOSSBilling Affected 0.5.4 to before 0.8.0 Fixed in 0.8.0 Patch available CNA

Remediation

Fix · CNA FOSSBilling (FOSSBilling) Fixed in 0.8.0

Timeline

2026-10-02 Threatist record created from CVE-2026-27604
2026-10-13 EPSS moved to the 50th–90th percentile

References

Other 2

TI-2023-03258 SQL Injection in fossbilling/fossbilling CVSS 3.1CRITICAL 9.8
TI-2023-03719 Insufficient Session Expiration in fossbilling/fossbilling CVSS 3.1CRITICAL 9.8
TI-2023-03259 Unrestricted Upload of File with Dangerous Type in fossbilling/fossbilling CVSS 3.1HIGH 8.8
TI-2023-03261 Improper Neutralization of Formula Elements in a CSV File in fossbilling/fossbilling CVSS 3.1HIGH 8.0
TI-2026-30636 FOSSBilling missing authorization in guest Invoice API endpoints CVSS 4.0HIGH 7.7
TI-2023-03173 Code Injection in fossbilling/fossbilling CVSS 3.1HIGH 7.2

See all 43 →

Sources

This product uses the NVD API but is not endorsed or certified by the NVD. Sources and licences