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CVE-2026-84390 – Authentication Bypass via Hardcoded JWT Secret – FortiMonitorOnSight 7.2.0–7.2.7

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Summary

CVE-2026-84390 is a critical vulnerability (CWE-540: Inclusion of Sensitive Information in Source Code) affecting the FortiMonitorOnSight web portal. A hardcoded/exposed secret embedded in the application’s source code allows a remote, unauthenticated attacker to forge or reuse a valid JSON Web Token (JWT) and bypass authentication entirely, gaining administrative-level access to the portal. The issue carries a CVSS v3.1 base score of 9.6 (Critical).

Technical details

  • Root cause: Sensitive information (a JWT signing/verification secret) is embedded directly in FortiMonitorOnSight’s source code (CWE-540), rather than being generated or stored securely.
  • Trigger conditions: No authentication, privileges, or user interaction are required — an attacker only needs network access to the exposed FortiMonitorOnSight web portal.
  • Attack vector: Network. An attacker can craft or replay a forged JWT signed with the exposed secret to impersonate legitimate users or administrators.
  • Impact: Full authentication bypass leading to unauthorized administrative access to the FortiMonitorOnSight portal, which centralizes enterprise monitoring data and controls — resulting in high impact to confidentiality, integrity, and availability.

Affected software

  • FortiMonitorOnSight version 7.2.0 through 7.2.2
  • FortiMonitorOnSight version 7.2.4 through 7.2.7

Severity

  • CVSS v3.1 Base Score: 9.6 (Critical)
  • Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

Mitigation and recommended actions

  • Immediate: Upgrade FortiMonitorOnSight to version 7.2.8 or later, where the exposed secret has been remediated.
  • If immediate patching is not possible: Restrict network exposure of the FortiMonitorOnSight web portal to trusted management networks only (e.g., via firewall rules or VPN), and avoid exposing the portal directly to the internet until patched. Monitor authentication logs for anomalous or unexpected administrative sessions.
  • As with any authentication-bypass fix, consider invalidating existing sessions/tokens and rotating any credentials accessible through the portal after upgrading.

References

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