CVE-2026-28496
CriticalExploitedVersions prior to 0.8.0 have a Server-Side Template Injection (SSTI) vulnerability in the template rendering system.
Published Jun 23, 2026 · Updated Aug 12, 2026
Key Facts
Patch immediately- CVE-2026-28496 is a critical-severity vulnerability (CVSS 9.4 v4) affecting FOSSBilling.
- It is exploited in the wild, listed in Industry KEV feed, CIRCL KEV since Jun 25, 2026. No public exploit code is known.
- EPSS estimates a 1.9% probability of exploitation in the next 30 days.
- No fixed version is listed yet; check the vendor advisory for mitigations.
- Brandefense priority: patch immediately, because it is listed as exploited in the wild.
CVSS v4
9.4
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
EPSS (30-day exploit likelihood)
1.9%
Higher than 79.3% of all scored CVEs
Exploited in the wild
Yes
2 catalog listings
Public exploit code
None known
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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.
Known-Exploited Catalog Listings
| Catalog | Added | Remediation due | Ransomware use |
|---|---|---|---|
| Industry KEV feed | Jun 25, 2026 | n/a | Not reported |
| CIRCL KEV | Aug 3, 2026 | n/a | Not reported |
Required action: Apply remediations or mitigations per vendor instructions or discontinue use of the product if remediation or mitigations are unavailable.
Affected Products
1 affected entries in total| Product | Affected versions | Fixed in |
|---|---|---|
| FOSSBilling | >= < 0.8.0 | n/a |
Timeline
Publicly disclosed
Jun 23, 2026
Added to Industry KEV feed
Jun 25, 2026
Added to CIRCL KEV
Aug 3, 2026
Last updated
Aug 12, 2026
Weakness Type
- CWE-1336 Improper Neutralization of Special Elements Used in a Template Engine
References
- advisorycve.org · CVERecord
- advisorynvd.nist.gov · CVE-2026-28496
- exploitVulnCheck exploitation report
- exploitVulnCheck exploitation report
- exploitVulnCheck exploitation report
FAQ
Common Questions.
FOSSBilling is a free, open-source billing and client management system.
Affected: FOSSBilling versions >= < 0.8.0. The full list is in the CVE brief.
It is exploited in the wild, listed in Industry KEV feed, CIRCL KEV since Jun 25, 2026.
No, it is not currently listed in the CISA Known Exploited Vulnerabilities catalog.
No public exploit code is known.
No fixed version is listed yet; check the vendor advisory for mitigations.
Brandefense priority: patch immediately, because it is listed as exploited in the wild.
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