# CVE-2026-43927: FOSSBilling has race condition in cart checkout that bypasses promo code usage limits


- **Severity:** Medium 6.9 (`CVSS:4.0/AV:N/AC:L/AT:N/PR:N/UI:N/VC:N/VI:L/VA:N/SC:N/SI:N/SA:N`)
- **Exploited in the wild:** Not known
- **Fix available:** No
- **Published:** 6 Jul 2026
- **Updated:** 7 Jul 2026
- **Also known as:** GHSA-w898-cx35-25gh

## What is CVE-2026-43927?

CVE-2026-43927 is a medium-severity vulnerability in FOSSBilling, published on 6 Jul 2026. 

### Official description

FOSSBilling is a free, open-source billing and client management system. Prior to version 0.8.0, a race condition in the cart checkout flow allows an authenticated client to apply a promo code beyond its configured maximum uses. By sending concurrent checkout requests before any single request completes the usage increment, a client can obtain unlimited discounted or free orders from a single-use or limited-use promo code. Version 0.8.0 patches the issue. Some workarounds are available. Disable promo codes entirely until a patch is available or monitor the `promo` table for `used` values exceeding `maxuses` and manually review affected orders.

Weakness: CWE-367 (Time-of-check Time-of-use (TOCTOU) Race Condition)

## Which versions are affected by CVE-2026-43927?


## How do I fix CVE-2026-43927?

No fix has been published for CVE-2026-43927 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-43927 being exploited?

There is no known exploitation of CVE-2026-43927 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-43927 and fix it if it is affected.

What it is: CVE-2026-43927 is a medium-severity vulnerability in FOSSBilling, published on 6 Jul 2026. 
Exploitation: There is no known exploitation of CVE-2026-43927 in the wild and no public exploit code.

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-2026-43927/ (Markdown: https://insights.sbomify.com/CVE-2026-43927/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-43927
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-43927
- OSV: https://osv.dev/vulnerability/CVE-2026-43927

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-43927/
Summaries are generated and may contain mistakes; the official description above is the record.