CVE-2026-28496

CVE-2026-28496 has been observed exploited in the wild (reported by VulnCheck KEV). EIP tracks 1 public exploit from researchers including rootdirective-sec. A Nuclei detection template is also available.

AI-analyzed exploit summary This repository contains a functional PoC for CVE-2026-28496, demonstrating a Server-Side Template Injection (SSTI) vulnerability in FOSSBilling's Twig rendering. The PoC sends a crafted template payload to the `/api/system/system/string_render` endpoint and checks if the server evaluates the expression, confirming vulnerability.

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.