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Information ExposureWeakness · CWE-200

CVE-2026-27604

CRITICAL · 10.0 CVSS v4.0 Published 2026-06-23
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
100/100
Remediation priority · Urgent
Remotely reachable No privileges Zero-click

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
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.

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis · high confidence

This is a critical authorization bypass in FOSSBilling where the API role handling incorrectly maps the `system` identity to cron admin privileges, allowing unauthenticated attackers to invoke privileged `/api/system/*` endpoints without any credentials, session, or CSRF token. This grants full administrative access to the billing system.

MitigationUpgrade to version 0.8.0 immediately, and implement defense-in-depth by blocking external access to `/api/system/*` at the WAF/reverse proxy, restricting API access to trusted IPs, rotating all admin/client API tokens, and invalidating active sessions.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Network
Complexity
Low
Privileges
None
Authentication
X
User interaction
None
Scope
X

CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:H/VI:H/VA:H/SC:H/SI:H/SA:H/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Verify FOSSBilling is installed
    Look for the FOSSBilling installation directory (commonly /var/www/fossbilling, /var/www/html/fossbilling, or similar). Check for characteristic files such as index.php, composer.json, or src/ directory with FOSSBilling code.
    Affected if FOSSBilling is not present on the system
  2. Determine the installed FOSSBilling version
    Check the composer.json file in the installation root for the 'version' field, or look for a VERSION file in the root directory. Alternatively, check the src/Version.php file if it exists.
    Affected if The installed version is lower than 0.8.0 (compare your version to the affected ranges)
  3. Verify API endpoint accessibility
    Send a request to http://your-server/api/system/info or similar /api/system/* endpoint without any authentication headers, session cookie, or CSRF token. Use: curl -s http://TARGET_HOST/api/system/info
    Affected if The API returns a successful response with system information or admin-level data without requiring any credentials
  4. Check network exposure of API endpoints
    Review your web server (Apache/Nginx) configuration and firewall rules to determine if the /api/ endpoint is exposed to untrusted networks or the public internet.
    Affected if The API endpoints are reachable from external/untrusted networks

The environment is affected if FOSSBilling version is below 0.8.0 AND the /api/system/* endpoint responds to unauthenticated requests.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Mitigation available No clean upgrade yet — mitigate in the meantime
Mitigation

Upgrade to version 0.8.0 immediately, and implement defense-in-depth by blocking external access to `/api/system/*` at the WAF/reverse proxy, restricting API access to trusted IPs, rotating all admin/client API tokens, and invalidating active sessions.

Recommended fix High confidence

FOSSBilling version 0.8.0

  1. Upgrade FOSSBilling to version 0.8.0 or later to patch the authorization bypass vulnerability
  2. After upgrading, rotate all admin and client API tokens as a precautionary measure
  3. Invalidate all active sessions and reset high-privilege credentials
  4. Review API request logs for any suspicious `/api/system/` access that may indicate exploitation
  5. If immediate upgrade is not possible, configure reverse proxy or WAF to block external access to `/api/system/*` endpoints
  6. Alternatively, restrict API access by configuring trusted source IPs using the `api.allowed_ips` configuration option

Generated from the published advisory — verify against the referenced sources before acting.

Have this fixed Scoped from the published advisory
  • Consultation4.0 h
  • Implementation8.0 h
  • Testing6.0 h
  • Review / QA4.0 h
22.0 hours of engineering $3,860
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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2026-27604 in production — separate from our analysis above.

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
  • No weaponised exploit code, or anything meant to cause harm
  • No spam, self-promotion, credentials, or personal data