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

Vulnerability from cvelistv5 – Published: 2026-06-23 14:20 – Updated: 2026-06-23 15:04
VLAI Shadowserver KEVIntel
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 (v2.0.3)
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.
Shadowserver
Known Exploited Vulnerability - GCVE BCP-07 Compliant
KEV entry ID: 88200ffd-9c29-4264-9c5a-cf89d01097a0

Vulnerability ID: CVE-2026-28496

Status: Confirmed

Status Updated: 2026-08-06 00:00 UTC

Exploited: Yes

Characteristics
Severity: 94.0
Timestamps
First Seen: 2026-08-03
Asserted: 2026-08-03
Last Seen: 2026-08-06
Scope
Asset Exposure: ['internet-facing']
Notes: Affected: FOSSBilling / FOSSBilling | Class: other-software | Severity: Critical (CVSS 9.4) | IoT: no | In CISA KEV: no | Honeypot connections on 2026-08-06: 3
Evidence

Type: Honeypot

Signal: In The Wild Attempts

Confidence: 70%

Source: shadowserver

Details
1D 1
Iot no
Feed Shadowserver Foundation honeypot/exploited-vulnerabilities
Type http-scan
Class other-software
7D Avg 0
Vendor FOSSBilling
30D Avg 0
90D Avg 0
Product FOSSBilling
Cisa Kev no
Connections 3
Observation Date 2026-08-06
Vulnerability Class CVSS
Vulnerability Score 9.4
Vulnerability Severity Critical
References
Created: 2026-08-05 01:00 UTC | Updated: 2026-08-08 01:23 UTC
KEVIntel
Known Exploited Vulnerability - GCVE BCP-07 Compliant
KEV entry ID: 985fe015-dcb1-4491-b111-0e50c961e2ab

Vulnerability ID: CVE-2026-28496

Status: Confirmed

Status Updated: 2026-08-03 00:00 UTC

Exploited: Yes

Timestamps
First Seen: 2026-08-03
Asserted: 2026-08-03
Scope
Notes: FOSSBilling: Server-side template injection in Twig template rendering enables information disclosure and RCE | Affected: FOSSBilling / FOSSBilling | CVSS: 9.4 (CRITICAL) | EPSS: 0.17612 | Used in malware: unknown | Not yet in CISA KEV: True
Evidence

Type: Public Report

Signal: Successful Exploitation

Confidence: 70%

Source: kevintel

Details
Feed KEVIntel (kevintel.com)
Title FOSSBilling: Server-side template injection in Twig template rendering enables information disclosure and RCE
Vendor FOSSBilling
Product FOSSBilling
Added Date 2026-08-03T00:00:00.000Z
Cvss Score 9.4
Epss Score 0.17612
Cvss Severity CRITICAL
Epss Percentile 0.96841
Used In Malware unknown
Ahead Of Cisa Kev None
Not Yet In Cisa Kev True
References
Created: 2026-08-04 11:00 UTC | Updated: 2026-08-04 11:00 UTC
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

Author Source Type Date Other

Nomenclature

  • Seen: The vulnerability was mentioned, discussed, or observed by the user.
  • 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.
  • Exploited: The vulnerability was observed as exploited by the user who reported the sighting.
  • Patched: The vulnerability was observed as successfully patched by the user who reported the sighting.
  • 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.


Detection rules are retrieved from Rulezet.