CVE-2026-28496
CRITICALEPSS 97th pctlDescription
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.
How to fix
No published remediation has been found for this vulnerability's affected products yet.
Mitigation guidance may be in the linked vendor advisories in the References section below.
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CVSS v4 Vector
Exploitability
Impact
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/E:X/CR:X/IR:X/AR:X/MAV:X/MAC:X/MAT:X/MPR:X/MUI:X/MVC:X/MVI:X/MVA:X/MSC:X/MSI:X/MSA:X/S:X/AU:X/R:X/V:X/RE:X/U:X
Exploit Intelligence
Very high risk: more likely to be exploited than 97% of all known CVEs.
References
Related Vulnerabilities
Other CWE-1336 vulnerabilities, ordered by exploit likelihood. View all
| CVE | Severity | CVSS | EPSS | Exploited | Fix |
|---|---|---|---|---|---|
| CVE-2024-4040 | Critical | 9.8 | 100% | KEV | Fix |
| CVE-2024-23692 | Critical | 9.8 | 99% | KEV + Ransom | - |
| CVE-2025-47916 | Critical | 10.0 | 85% | - | Fix |
| CVE-2024-32651 | Critical | 10.0 | 84% | - | - |
| CVE-2022-25813 | High | 7.5 | 67% | - | Fix |
| CVE-2025-34300 | Unscored | - | 51% | - | - |
Common questions
How do I fix CVE-2026-28496?
No published fix for CVE-2026-28496 has been found yet. Check the linked vendor advisories for guidance as it becomes available.
Is CVE-2026-28496 being actively exploited?
Not that we know of. CVE-2026-28496 is not in the CISA Known Exploited Vulnerabilities catalog. Its EPSS score of 17.6% is the estimated probability that it will be exploited in the next 30 days. That is higher than 97% of all scored CVEs.
How severe is CVE-2026-28496?
CVE-2026-28496 has a CVSS v4 base score of 9.4, rated critical. CVSS rates the technical impact if the vulnerability is exploited, not how likely that is, so weigh it alongside the exploit-prediction score when you decide what to patch first.
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This product uses NVD data but is not endorsed or certified by the NVD. EPSS scores courtesy of FIRST.org (https://www.first.org/epss). Source: CISA KEV Catalog. Data as of 2026-06-23.