CVE-2026-28496criticalobserved exploitationCWE-1336

CVE-2026-28496: critical vulnerability in FOSSBilling

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

Published

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85Vexday Risk Score

Patch now. It exploitation observed by VulnCheck and has a working public exploit.

ssvc Actcvss 9.4epss 1.9%
from disclosure to weapon6 days
Published on NVDJun 23
1st PoC+6d
VulnCheck+2d
In short

FOSSBilling before version 0.8.0 allows administrators to inject malicious code into email templates and other Twig-rendered content, which can be executed by the server to steal data or take control of the system.

Technical detail

Server-Side Template Injection (SSTI) in Twig template rendering affects FOSSBilling <0.8.0; authenticated administrators can inject arbitrary Twig expressions via email templates, mass mail campaigns, custom payment adapters, and the string_render API endpoint. The lack of Twig sandbox allows access to the full environment, API context, and dependency injection container, enabling information disclosure and remote code execution.

Summary generated and translated by AI from the 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.
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
Affected products
FOSSBilling · FOSSBilling
⚠ Public resources, to assess the exposure of systems you control or are authorized to test. Test only with authorization.
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