# CVE-2026-43921: FOSSBilling vulnerable to arbitrary PHP code injection via unescaped config serialization

> An attacker with admin privileges can inject arbitrary PHP code into configuration files, leading to remote code execution on every subsequent request.

- **Severity:** High 8.9 (`CVSS:4.0/AV:N/AC:L/AT:P/PR:H/UI:N/VC:H/VI:H/VA:H/SC:H/SI:H/SA:H`)
- **Exploited in the wild:** Not known
- **Login needed:** An administrator
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 6 Jul 2026
- **Updated:** 7 Jul 2026
- **Also known as:** GHSA-v4j9-w6pj-38w5

## What is CVE-2026-43921?

CVE-2026-43921 is a high-severity code injection vulnerability in FOSSBilling, published on 6 Jul 2026. An attacker needs administrator access to exploit it, with no action from the victim.

### Official description

FOSSBilling is a free, open-source billing and client management system. Versions 0.6.10 through 0.7.2 have a PHP code injection vulnerability in FOSSBilling's `Config::prettyPrintArrayToPHP()` method. When configuration values are updated, string values are written into `config.php` without escaping single quotes. Because `config.php` is loaded via a bare `include` on every HTTP request, an attacker with admin privileges can inject arbitrary PHP code that executes on every subsequent request. Version 0.8.0 contains a patch. Some workarounds are available. Restrict admin access to trusted personnel only; audit `config.php` for unexpected PHP code; and/ or at the reverse proxy/WAF level, restrict access to admin API endpoints that modify configuration.

Weakness: CWE-94 (Improper Control of Generation of Code)

## Which versions are affected by CVE-2026-43921?


## How do I fix CVE-2026-43921?

No fix has been published for CVE-2026-43921 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-43921 being exploited?

There is no known exploitation of CVE-2026-43921 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-43921 and fix it if it is affected.

What it is: CVE-2026-43921 is a high-severity code injection vulnerability in FOSSBilling, published on 6 Jul 2026. An attacker needs administrator access to exploit it, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-43921 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-2026-43921/ (Markdown: https://insights.sbomify.com/CVE-2026-43921/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-43921
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-43921
- OSV: https://osv.dev/vulnerability/CVE-2026-43921

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-43921/
Summaries are generated and may contain mistakes; the official description above is the record.