CVE-2026-28496: FOSSBilling: Server-side template injection in Twig template rendering enables information disclosure and RCE

1. In CISA KEV: not seen
2. Exploited (reported): not seen
3. Scanning observed: not seen
4. Proof of concept public2 public GitHub repositories (unverified), listed by PoC-in-GitHub29 Jun
5. Not established: not seen

DescriptionNVD

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.

Exploitation

Check available, not yet exploited. A public nuclei template can confirm it on a system you are authorised to test.

CISA KEV

Not listed

Public check

FOSSBilling - Server-Side Template Injection · nuclei template in projectdiscovery/nuclei-templates

Weakness

Improper Neutralization of Special Elements Used in a Template Engine · Command and Code Injection

Vendor

FOSSBilling

Published

June 2026

Band

Check available, not yet exploited, June 2026

1. 29 Jun
   PoC-in-GitHub lists 2 public GitHub repositories (unverified) PoC-in-GitHub

• NVD entrynvd.nist.gov
• Vendor advisorygithub.com
• CVE recordcve.org
• Weakness CWE-1336cwe.mitre.org