Which versions of FOSSBilling are affected by EUVD-2026-38455?

A critical vulnerability in FOSSBilling versions prior to 0.8.0 enables authenticated administrators to execute arbitrary code within the billing system infrastructure; no public exploit identified…. A patch is available.

Is there a public PoC exploit available for EUVD-2026-38455?

Yes, a public proof-of-concept exploit is available for EUVD-2026-38455. Prioritise patching immediately. EPSS: 1.9%.

How to fix or mitigate EUVD-2026-38455?

Within 24 hours: Enumerate and audit all FOSSBilling administrator accounts; disable template-editing features if operationally feasible; enable comprehensive audit logging of admin activities. Within 7 days: Reduce administrator access to only essential personnel and enforce multi-factor authentication; implement strict network segmentation isolating FOSSBilling from other systems; monitor for indicators of exploitation. Within 30 days: Deploy FOSSBilling 0.8.0 immediately upon release; continuously monitor vendor advisory channels and GHSA-78x5-c8gw-8279 for critical updates; if patching remains unavailable beyond 30 days, initiate migration to alternative billing platform.

FOSSBilling EUVD-2026-38455

Q: What is the CVSS score of EUVD-2026-38455?

EUVD-2026-38455 has a CVSS 4.0 base score of 9.4 (Critical). CVSS 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/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. EPSS exploitation probability: 1.9%.

| CVE-2026-28496 CRITICAL

Improper Neutralization of Special Elements Used in a Template Engine (CWE-1336)

2026-06-23 GitHub_M

Ssti RCE Information Disclosure Fossbilling

9.4

CVSS 4.0 · Vendor: GitHub_M

Severity by source

Vendor (GitHub_M) PRIMARY

9.4 CRITICAL

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

vuln.today AI

9.1 CRITICAL

Network-reachable admin endpoints (AV:N/AC:L), administrator role required (PR:H), no user interaction, and template engine breakout impacts other components (S:C) with full CIA loss.

3.1 AV:N/AC:L/PR:H/UI:N/S:C/C:H/I:H/A:H

4.0 AV:N/AC:L/AT:N/PR:H/UI:N/VC:H/VI:H/VA:H/SC:H/SI:H/SA:H

Primary rating from Vendor (GitHub_M).

CVSS VectorVendor: GitHub_M

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

Attack Vector

Network

Attack Complexity

Low

Privileges Required

High

User Interaction

None

Scope

Lifecycle Timeline

Patch available

Jun 23, 2026 - 16:01 EUVD

Analysis Generated

Jun 23, 2026 - 15:05 vuln.today

DescriptionCVE.org

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.

AnalysisAI

Server-side template injection in FOSSBilling versions prior to 0.8.0 allows authenticated administrators to execute arbitrary code and disclose sensitive information by injecting Twig expressions into template-rendering features. The unsandboxed Twig environment exposes the application's dependency injection container, turning any admin-accessible template surface into a full RCE primitive. No public exploit identified at time of analysis, but a related auth-bypass chain (GHSA-78x5-c8gw-8279) is documented by VulnCheck and could lower the practical privilege bar.

Technical ContextAI

FOSSBilling is a PHP-based open-source billing and client management platform that uses the Twig templating engine to render email templates, mass-mail campaigns, custom payment adapters, and content passed to the string_render API endpoint. CWE-1336 (Improper Neutralization of Special Elements Used in a Template Engine) applies here because Twig is invoked without the sandbox extension, so rendered templates have unrestricted access to the full Twig environment, the API context, and the Symfony-style dependency injection container - including service objects that wrap filesystem, database, and shell-adjacent functionality. The affected CPE is cpe:2.3:a:fossbilling:fossbilling:*:*:*:*:*:*:*:* covering all versions before 0.8.0.

RemediationAI

Vendor-released patch: upgrade FOSSBilling to 0.8.0 or later per advisory GHSA-57mv-jm88-66jc (https://github.com/FOSSBilling/FOSSBilling/security/advisories/GHSA-57mv-jm88-66jc). If immediate upgrade is not possible, audit all stored email templates, mass-mail campaign bodies, and custom payment adapter templates for unexpected Twig expressions such as {{ ... }} blocks referencing _self, app, or container services, then rotate every admin and client API token to invalidate credentials potentially harvested by prior abuse. To prevent chaining with the auth-bypass issue tracked as GHSA-78x5-c8gw-8279, block external access to /api/system/* at the reverse proxy or WAF - note the trade-off that this will also break any legitimate integrations that rely on the system API surface, so allowlist trusted internal IPs rather than dropping the rule entirely if such integrations exist.