CVE-2026-28496 (GCVE-0-2026-28496)

Vulnerability from cvelistv5 – Published: 2026-06-23 14:20 – Updated: 2026-06-23 15:04
VLAI Previdian
Title
FOSSBilling: Server-side template injection in Twig template rendering enables information disclosure and RCE
Summary
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.
Severity
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
SSVC
Exploitation: none Automatable: no Technical Impact: total
CISA Coordinator · CISA-ADP (v2.0.3)
Decision recorded 2026-06-23 15:02 UTC
CWE
  • CWE-1336 - Improper Neutralization of Special Elements Used in a Template Engine
Assigner
References
Impacted products
Vendor Product Version
FOSSBilling FOSSBilling Affected: < 0.8.0
Create a notification for this product.
Previdian
Known Exploited Vulnerability - GCVE BCP-07 Compliant
KEV entry ID: 8267092f-8e72-4c05-9b7e-3a23d9223666

Vulnerability ID: CVE-2026-28496

Status: Confirmed

Status Updated: 2026-08-04 15:25 CEST

Exploited: Yes

Timestamps
First Seen: 2026-08-04
Asserted: 2026-08-04
Scope
Notes: FOSSBilling: Server-side template injection in Twig template rendering enables information disclosure and RCE | Affected: FOSSBilling / FOSSBilling | CVSS: 9.4 (CRITICAL) | EPSS: 0.01905 | Used in malware: unknown | Not yet in CISA KEV: True
Evidence

Type: Public Report

Signal: Successful Exploitation

Confidence: 70%

Source: previdian

Details
Feed Previdian (previdian.com)
Title FOSSBilling: Server-side template injection in Twig template rendering enables information disclosure and RCE
Cve Id CVE-2026-28496
Vendor FOSSBilling
Ghsa Id None
Product FOSSBilling
Added Date 2026-08-04T13:25:09.278Z
Cvss Score 9.4
Epss Score 0.01905
Previous Ids
Cvss Severity CRITICAL
Virtual Patch False
Cvss Estimated False
Epss Percentile 0.78983
Used In Malware unknown
Vulnerability Id CVE-2026-28496
Ahead Of Cisa Kev None
Not Yet In Cisa Kev True
References
Created: 2026-10-02 09:09 CEST | Updated: 2026-10-02 09:09 CEST
Show details on NVD website
To clipboard 

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Forecast uses a logistic model when the trend is rising, or an exponential decay model when the trend is falling. Fitted via linearized least squares.

Sightings

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Nomenclature

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  • Confirmed: The vulnerability has been validated from an analyst's perspective.
  • Published Proof of Concept: A public proof of concept is available for this vulnerability.
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  • Not exploited: The vulnerability was not observed as exploited by the user who reported the sighting.
  • Not confirmed: The user expressed doubt about the validity of the vulnerability.
  • Not patched: The vulnerability was not observed as successfully patched by the user who reported the sighting.



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