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

> Unauthenticated attackers can access privileged admin API endpoints in FOSSBilling due to improper role validation, allowing unauthorized system control.

- **Severity:** Critical 10.0 (`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`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 23 Jun 2026
- **Updated:** 23 Jun 2026

## What is CVE-2026-27604?

CVE-2026-27604 is a critical missing authorization vulnerability in FOSSBilling, published on 23 Jun 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.

### Official description

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.

Weakness: CWE-862 (Missing Authorization), CWE-863 (Incorrect Authorization), CWE-306 (Missing Authentication for Critical Functionality), CWE-200 (Exposure of Sensitive Information to an Unauthorized Actor)

## Which versions are affected by CVE-2026-27604?


## How do I fix CVE-2026-27604?

No fix has been published for CVE-2026-27604 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-27604 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-27604 exists.

Public exploit code:

- FOSSBilling 0.5.4-0.7.x - Unauthenticated System API Role Authorization Bypass (nuclei): http/cves/2026/CVE-2026-27604.yaml

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-27604 and fix it if it is affected.

What it is: CVE-2026-27604 is a critical missing authorization vulnerability in FOSSBilling, published on 23 Jun 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-27604 exists.

Affected product: FOSSBilling. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-27604/ (Markdown: https://insights.sbomify.com/CVE-2026-27604/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-27604
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-27604
- OSV: https://osv.dev/vulnerability/CVE-2026-27604

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-27604/
Summaries are generated and may contain mistakes; the official description above is the record.