Is CVE-2026-28496 actively exploited?

Yes. KEVIntel has observed exploitation attempts targeting this CVE. Confidence is confirmed.

What exploitation activity has KEVIntel observed?

KEVIntel sensors have observed 3 exploitation attempts, 3 unique attacker IPs, and 3 countries targeting CVE-2026-28496. First observed Jul 19, 2026; last observed Jul 30, 2026.

Which versions are affected?

CVE-2026-28496 affects FOSSBilling FOSSBilling. Reported affected version: < 0.8.0.

How should organizations remediate it?

Prioritize immediate patching and validate internet-facing exposure. Monitor for matching exploitation attempts in your environment.

No. CVE-2026-28496 is not currently listed in CISA KEV.

Vulnerability report

Active exploitation observed Confirmed confidence Not in CISA KEV

CVE-2026-28496

Q: How should organizations remediate it?

Prioritize immediate patching and validate internet-facing exposure. Monitor for matching exploitation attempts in your environment.

Q: Is it in CISA KEV?

No. CVE-2026-28496 is not currently listed in CISA KEV.

FOSSBilling Information Disclosure

FOSSBilling / FOSSBilling · affected before 0.8.0

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Severity: CVSS 9.4 · Critical
Confidence: Confirmed
Exploit status: Observed in sensors
EPSS: 17.6%
First observed: 19 Jul 2026
Last observed: 30 Jul 2026

Decision summary

What security teams need to know first

Direct answers before the deeper technical record.

What it is

CVE-2026-28496 is a vulnerability affecting FOSSBilling FOSSBilling. FOSSBilling is a free, open-source billing and client management system. Versions prior to 0.8.0 have a Server-Side Template Injection (SSTI)...

Is it exploited?

Yes. KEVIntel sensors observed exploitation attempts with confirmed confidence.

Who is affected?

FOSSBilling / FOSSBilling affected before 0.8.0.

What should we do?

Patch immediately, validate internet-facing exposure, and monitor for matching requests.

Overview

FOSSBilling is a free, open-source billing and client management system

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.

Vendor Product Affected Status

FOSSBilling FOSSBilling Before 0.8.0 Affected

Published: 23 Jun 2026
Exploited Since: 19 Jul 2026
Attack vector: Remote
Complexity: Low
Privileges: High
User interaction: None

CVE References

https://github.com/FOSSBilling/FOSSBilling/security/advisories/GHSA-57mv-jm88-66jc github.com · CVE Record https://github.com/FOSSBilling/FOSSBilling/security/advisories/GHSA-5...
https://github.com/FOSSBilling/FOSSBilling/security/advisories/GHSA-78x5-c8gw-8279 github.com · CVE Record https://github.com/FOSSBilling/FOSSBilling/security/advisories/GHSA-7...
https://www.vulncheck.com/blog/fossbilling-auth-bypass-ssti-rce vulncheck.com · CVE Record https://www.vulncheck.com/blog/fossbilling-auth-bypass-ssti-rce

Exploitation evidence

Why KEVIntel marks this CVE as exploited

Third-party attestation and first-party sensor observation are shown separately so teams can judge the evidence chain.

Exploited in the wild

The Shadowserver

Recorded 03 Aug 2026

Independent exploitation attestation added to the KEVIntel record.

Active exploitation observed

KEVIntel sensor

First observed 19 Jul 2026

First-party sensor telemetry confirms matching exploitation attempts.

Proof of concept available

Nuclei Templates

Recorded 24 Jun 2026

Public scanner or PoC coverage increases practical exploitability.

Known exploited vulnerability sources

Per-source evidence links for KEV attestations are available through the KEVIntel Pro API.

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Source	Added
The Shadowserver First	2026-08-03 00:00 UTC
KEVIntel	2026-08-04 13:25 UTC

Operational indicators for this CVE are listed under Detection.

Sensor telemetry

First-party evidence of exploitation activity

Aggregate observations show the scale, recency, and distribution of activity without overstating sparse data.

Attempts observed

Unique attacker IPs

Attacker countries

JP · NL · US

Sensors observed

Exploitation attempts over the last 19 days

Daily events observed by KEVIntel sensors

Updated 05 Aug 2026

First observed 19 Jul 2026 · Last observed 30 Jul 2026

Pro adds sensor region and window summaries. Enterprise adds raw IPs, paths, User-Agents, and payloads.

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Detection

Operational artifacts and observed signals

Make the evidence actionable in scanner, SOC, and edge-control workflows.

Observed signals

Request targets: 1
User-Agents: 3

Raw values available in Pro and Enterprise.

Scanner coverage

Nuclei template detected 24 Jun 2026.

View Nuclei template

Virtual patch status

No KEVIntel virtual patch is currently available. Future rules ship for ModSecurity, Cloudflare, and AWS WAF.

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Attacker IP Indicators

Attacker IP indicators observed · available in Pro and Enterprise.

Sensor-derived attacker IP indicators are available to Pro and Enterprise accounts under Detection and through the Pro API.

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Scanner Artifacts

Scanner and exploit-framework references linked to this CVE.

Scanner	Reference	Detected
Nuclei	https://github.com/projectdiscovery/nuclei-templates/blob/main/http/cves/2026/CVE-2026-28496.yaml	24 Jun 2026

Risk and context

Severity, weaknesses, and research context

CVSS v4.0

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

EPSS

17.6%

Weaknesses

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

Potential Proof of Concepts

These PoCs are unverified and could contain malware. Use at your own risk.

rootdirective-sec/CVE-2026-28496-Lab

github · Created 2026-06-29 14:39:05 UTC · 0 stars

FOSSBilling - Server-Side Template Injection

nuclei · Created Unknown

Timeline

From disclosure to observed exploitation

03 Aug 2026
Added to KEVIntel KEV Feed

High-confidence, third-party attested exploitation
19 Jul 2026
Observed by KEVIntel sensors

Evidence-backed exploitation signal
19 Jul 2026
Indicators of compromise added (3)

Indicators of compromise recorded
24 Jun 2026
Public PoC available

Public proof-of-concept code published
24 Jun 2026
Nuclei template available

Scanner coverage available
23 Jun 2026
CVE published

Vulnerability disclosed publicly
27 Feb 2026
CVE ID reserved

Identifier reserved by the CNA

Pro API

Automate this intelligence

Confidence, exploit status, sensor telemetry, PoCs, scanner integrations, mentions, and tags are available programmatically for VM, SOC, and CTI workflows.

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Evidence confidence and provenance
First-party sensor telemetry
PoC and scanner references
Affected versions and enrichment
Automation-ready JSON delivery

GET /api/v2/pro/kevs/CVE-2026-28496

Free JSON includes basic KEV fields

{
  "cve_id": "CVE-2026-28496",
  "confidence": "Confirmed",
  "cvss_score": 9.4,
  "epss_score": 0.17612,
  "exploit_status": {
    "exploited_in_the_wild": true,
    "active_exploitation_observed": true
  },
  "sensor_telemetry": { "attempts": 3, "sensors": 3 }
}

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