CVE-2026-28496 FOSSBilling: Server-side template injection in Twig template rendering enables information disclosure and RCE
Administrators can inject Twig expressions to achieve remote code execution and information disclosure in FOSSBilling.
- Exploited in the wild
- Not known
- Login needed
- An administrator
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- None listed
What is CVE-2026-28496?
CVE-2026-28496 is a critical code injection vulnerability in FOSSBilling, published on 23 Jun 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 prior to 0.8.0 have a Server-Side Template Injection (SSTI) vulnerability in the template rendering system. Administrators with access to features that render Twig templates (email templates, mass mail campaigns, custom payment adapters, and the `string_render` API endpoint) can inject arbitrary Twig expressions, leading to information disclosure and remote code execution. The vulnerability exists because Twig templates are rendered without a sandbox, allowing access to the full Twig environment, API context, and the application's dependency injection container. Version 0.8.0 patches the issue. Some workarounds are available. Audit existing email templates for suspicious Twig expressions, rotate all admin and client API tokens, and/or block external access to /api/system/* at reverse proxy/WAF to mitigate chaining with GHSA-78x5-c8gw-8279.
Weakness: CWE-1336
Which versions are affected by CVE-2026-28496?
How do I fix CVE-2026-28496?
No fix has been published for CVE-2026-28496 yet. Limit exposure of the affected software until one is available.
Upgrade, and never evaluate templates, expressions or code built from user input. More about Code injection.
Is CVE-2026-28496 being exploited?
It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-28496 exists.
Public exploit code: 1 Nuclei template and 2 proofs of concept on GitHub.
Sources
Also known as CVE-2026-42347.