CVE-2026-28496

CRITICALPre-NVD 9.49.4—
EchelonGraph scoreMEDIUM confidence

This critical-severity CVE scores 9.4 under a secondary CVSS source (NVD's own analysis pending). EPSS exploit probability: 1.9%, top 23% of all CVEs by exploit prediction. GitHub Security Advisory data not yet ingested — confidence will rise once GHSA publishes (typical lag: hours to days for open-source ecosystem CVEs; never for infrastructure-only CVEs).

Triggered by: NVD CVSS baseline
Sources: epss, secondary
Elevated
9.4
EchelonGraph verdictPlan a fixSerious severity, but no confirmed exploitation yet.
  • High severity, but no confirmed exploitation yet
CISA-KEV: Not listedEPSS: 2%CVSS: 9.4Exploit: NoneExposed: 0

No vendor fix yet — apply a workaround or compensating control (WAF / firewall / segmentation) and watch for a patch.

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.

CVSS v3
9.4
EG Score
9.4(medium)
EPSS
77.1%
KEV
Not listed

Published

June 23, 2026

Last Modified

June 23, 2026

Advisory Details (3)

Auto-updated Jun 23, 2026
🔬 Proof of concept available. Patch available. Sources: github.
generic

CVE-2026-28496 - FOSSBilling Auth Bypass and Twig SSTI to Unauthenticated RCE | Blog | VulnCheck

https://www.vulncheck.com/blog/fossbilling-auth-bypass-ssti-rce
github Patch Available

Improper API role validation (system) enables unauthenticated access to privileged admin functions · Advisory · FOSSBilling/FOSSBilling · GitHub

https://github.com/FOSSBilling/FOSSBilling/security/advisories/GHSA-78x5-c8gw-8279
github Patch Available🟡 PoC Available

Server-side template injection in Twig template rendering enables information disclosure and RCE · Advisory · FOSSBilling/FOSSBilling · GitHub

https://github.com/FOSSBilling/FOSSBilling/security/advisories/GHSA-57mv-jm88-66jc

Weakness Classification(1)

MITRE Common Weakness Enumeration — the root-cause categories this CVE belongs to.

Data Freshness Timeline

(refreshed 54× in last 7d / 144× in last 30d)

Each row is a source pipeline that fetched or updated this CVE on that date, with what changed. For example, "NVD update" means NVD published or revised its analysis for this CVE; "MITRE cvelistV5" means we ingested or refreshed it from the CNA feed. Most recent first.

Showing the most recent 100 of 144 total refreshes for this CVE.

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Publicly available exploits

(1 reference)

Working exploit code is in the public domain. Defenders should treat patch urgency accordingly — public PoCs typically lead to mass-exploitation within 24-72 hours.

  • Nucleihttp/cves/2026/CVE-2026-28496.yaml
    First seen Jan 1, 2026

    FOSSBilling - Server-Side Template Injection

    Open source ↗

Frequently asked(5)

What is CVE-2026-28496?
CVE-2026-28496 is a critical vulnerability published on June 23, 2026. 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,…
When was CVE-2026-28496 disclosed?
CVE-2026-28496 was first published in the National Vulnerability Database on June 23, 2026. EchelonGraph re-ingests CVE updates from NVD on a 2-hour cycle, so this page reflects the latest published state.
Is CVE-2026-28496 actively exploited?
CVE-2026-28496 is not currently on CISA's Known Exploited Vulnerabilities catalog. FIRST EPSS estimates a 77.1% percentile likelihood of exploitation in the next 30 days — higher percentiles indicate greater predicted risk.
What is the CVSS score of CVE-2026-28496?
CVE-2026-28496 has a CVSS v3 base score of 9.4 (NVD).
How do I remediate CVE-2026-28496?
Patch to the fixed version published by the affected vendor. Where vendor advisories exist for CVE-2026-28496, EchelonGraph cross-links them in the Vendor Advisories panel below — those typically contain the canonical remediation steps, fixed version numbers, and any vendor-specific mitigations.

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