# CVE-2026-43921: FOSSBilling PHP code injection in Config component

Source: https://junglewise.ai/threats/cve-2026-43921-fossbilling-php-code-injection-in-config-component  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-07-06. Updated: 2026-07-06  
License: CC BY 4.0 with a link back

CVE-2026-43921 · Severity: info · CVSS 8.9 · Published 2026-07-06

FOSSBilling, an open-source billing and client management platform, contains a vulnerability that allows an administrator to take full control of the underlying server. By saving specially crafted configuration settings, an attacker can inject malicious code that runs automatically every time the application is accessed. This could lead to the theft of sensitive customer data, complete service disruption, or the use of the server for further attacks.

Technologies: [FOSSBilling](https://junglewise.ai/threats/technologies/fossbilling). Vendors: [FOSSBilling](https://junglewise.ai/threats/vendors/fossbilling).

## Quick answers

**Is CVE-2026-43921 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-43921 being exploited in the wild.

**How severe is CVE-2026-43921?** Informational severity, with a CVSS score of 8.9, published 6 July 2026.

**Which products and versions are affected?** FOSSBilling 0.6.10 - 0.7.2.

**Is there a fix for CVE-2026-43921?** No fixed version is recorded yet. Check the vendor's advisory in the references below. If you run it, Junglewise drafts a mitigation that fits your setup and applies it once you approve, with senior security engineers behind it.

**How is CVE-2026-43921 attacked?** It is attacked over the network, in a network appliance.

**Am I affected by CVE-2026-43921?** Check whether you run FOSSBilling at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## Technical details

A PHP code injection vulnerability exists in the `Config::prettyPrintArrayToPHP()` method of FOSSBilling. The root cause is a failure to escape single quotes when writing user-supplied configuration strings into the `config.php` file. An attacker with administrative privileges can use API endpoints like `set_interface_ip()` to inject arbitrary PHP code into the configuration file. Because `config.php` is loaded via a bare `include` statement on every HTTP request, the injected code executes with the privileges of the web server user. The vulnerability is patched in version 0.8.0.

## Affected products

- FOSSBilling FOSSBilling 0.6.10 - 0.7.2

## Timeline

- 2026-06-12: advisory: GitHub advisory published
- 2026-07-06: disclosed: NVD publication date

## References

- [https://github.com/FOSSBilling/FOSSBilling/security/advisories/GHSA-v4j9-w6pj-38w5](https://github.com/FOSSBilling/FOSSBilling/security/advisories/GHSA-v4j9-w6pj-38w5)

## Related threats

- [FOSSBilling stored XSS in support ticket notes](https://junglewise.ai/threats/cve-2026-111048-fossbilling-is-an-open-source-billing-and-client-management)
- [FOSSBilling CSRF vulnerability in staff guest login endpoint](https://junglewise.ai/threats/cve-2026-112374-fossbilling-before-0-8-9-contains-a-cross-site-request-forgery)
- [FOSSBilling email enumeration via guest signup endpoint](https://junglewise.ai/threats/cve-2026-111056-fossbilling-is-an-open-source-billing-and-client-management)
- [FOSSBilling path traversal in template_exists endpoint](https://junglewise.ai/threats/cve-2026-111053-fossbilling-is-an-open-source-billing-and-client-management)
- [FOSSBilling authorization bypass in extension configuration management](https://junglewise.ai/threats/cve-2026-111046-fossbilling-is-an-open-source-billing-and-client-management)