# CVE-2026-42331: FOSSBilling missing authorization in guest Invoice API endpoints

> Unauthenticated attackers can modify payment gateways on unpaid invoices if invoice hashes are exposed, requiring the accessible-from-hash setting to be enabled.

- **Severity:** High 7.7 (`CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:H/SA:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 6 Jul 2026
- **Updated:** 7 Jul 2026
- **Also known as:** GHSA-8755-w77f-3g7j

## What is CVE-2026-42331?

CVE-2026-42331 is a high-severity missing authorization vulnerability in FOSSBilling, published on 6 Jul 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. Prior to version 0.8.0, the Guest API invoice/update endpoint is missing an authorization check present in other invoice-related endpoints, allowing an unauthenticated user with knowledge of an invoice hash to modify the payment gateway associated with an unpaid invoice. An attacker who obtains an invoice hash, which may leak through shared URLs, referrer headers, or email links,  can change the `gateway_id` on an unpaid invoice to any payment gateway configured in the system. This does not allow redirecting payments to an arbitrary external endpoint, as the gateway must already be installed and configured by an administrator. The practical impact is further limited by the `invoice_accessible_from_hash` system setting. Version 0.8.0 contains a patch. No known workarounds are available.

Weakness: CWE-863 (Incorrect Authorization), CWE-306 (Missing Authentication for Critical Functionality)

## Which versions are affected by CVE-2026-42331?


## How do I fix CVE-2026-42331?

No fix has been published for CVE-2026-42331 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-42331 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-42331 exists.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-42331 and fix it if it is affected.

What it is: CVE-2026-42331 is a high-severity missing authorization vulnerability in FOSSBilling, published on 6 Jul 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-2026-42331 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-2026-42331/ (Markdown: https://insights.sbomify.com/CVE-2026-42331/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-42331
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-42331
- OSV: https://osv.dev/vulnerability/CVE-2026-42331

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-42331/
Summaries are generated and may contain mistakes; the official description above is the record.