CVE-2026-27604: 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.allowedips), 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.
Affected Software
Remediation
Recommended actions to resolve this vulnerability, in priority order.
- Upgrade
Upgrade
FOSSBillingto a version that resolves this vulnerability.Fixed in 0.8.0 - Configuration
Restrict API access by configuring api.allowed_ips to allow only trusted source IP addresses.
FOSSBilling api.allowed_ips = trusted source IPs only - Compensating control
Block external access to /api/system/* at the reverse proxy or WAF (deny requests to the /api/system/* path from untrusted networks).
- Operational
Rotate all admin and client API tokens immediately.
- Operational
Invalidate active sessions and reset high-privilege credentials.
- Operational
Review API request logs for suspicious /api/system/ access and treat any findings as a potential incident.
Event History
Frequently Asked Questions
What is the severity of CVE-2026-27604?
CVE-2026-27604 has a risk score of 86, indicating a high severity vulnerability.
How do I fix CVE-2026-27604?
To fix CVE-2026-27604, upgrade FOSSBilling to version 0.8.0 or later, where the authorization bypass is resolved.
What are the consequences of CVE-2026-27604?
CVE-2026-27604 allows unauthenticated users to access privileged admin functions through the API, potentially leading to unauthorized system changes.
Which versions of FOSSBilling are affected by CVE-2026-27604?
FOSSBilling versions from 0.5.4 to 0.8.0 are affected by CVE-2026-27604.
What type of vulnerability is CVE-2026-27604?
CVE-2026-27604 is classified as an authorization bypass vulnerability affecting the API role validation.