Fortinet Patches Critical Vulnerabilities in FortiMonitorOnSight, Chrome Extension

CVE-2026-26084 is an improper access control flaw (CWE-284) in the web interface of Fortinet's FortiSandbox threat-analysis product line, affecting on-premises 4.4.x and 5.0.x releases as well as the FortiSandbox Cloud and PaaS offerings. An unauthenticated attacker can trigger it remotely by sending crafted HTTP requests to the affected FortiSandbox web service, bypassing access controls without needing credentials or user interaction. A successful attacker gains access to sensitive information handled by the appliance; Fortinet's critical 9.9 CVSS score also reflects a scope change with a high availability-impact component, so defenders should treat the practical impact as potentially broader than simple information disclosure. Any organization running affected versions of FortiSandbox, FortiSandbox Cloud, or FortiSandbox PaaS is in scope, though the product's enterprise appliance/cloud deployment model means the affected population is far smaller than endpoint or firewall software. There is no evidence of exploitation so far: the flaw is not in CISA KEV, has no known public proof-of-concept, and EPSS assigns roughly a 0.2% probability of exploitation within 30 days.

Do: Upgrade all FortiSandbox deployments to a fixed release outside the affected ranges — later than 5.0.5 on the 5.0 branch, later than 4.4.8 on the 4.4 branch, and later than 5.0.5 for Cloud and PaaS — following Fortinet's PSIRT advisory. Until patched, restrict HTTP/HTTPS management access to the appliance to trusted management networks or VPN, since the flaw is reachable without authentication. Monitor Fortinet's advisory and the CISA KEV catalog for updates, given the critical severity score.

CVE-2026-84390 is a critical (CVSS 3.1: 9.8) information-disclosure flaw in Fortinet FortiMonitorOnSight in which sensitive information is included in the product's source code (CWE-540). An unauthenticated, network-located attacker who obtains that embedded material (e.g., secrets or credentials shipped with the code) can use it to gain improper access by subverting access controls; the CVSS vector requires no privileges or user interaction and rates the impact high on confidentiality, integrity, and availability. All FortiMonitorOnSight deployments running the affected 7.2.x releases listed by Fortinet (7.2.0 through 7.2.2 and 7.2.4 through 7.2.7) are affected. Fortinet has shipped fixes for this flaw, but there is no public proof-of-concept, the vulnerability is not in CISA KEV, and no exploitation in the wild is currently known.

Do: Upgrade FortiMonitorOnSight to a fixed release per Fortinet's PSIRT advisory, i.e., any version superseding the listed 7.2.0-7.2.2 and 7.2.4-7.2.7 ranges. Because the flaw involves sensitive material in source code, also rotate any credentials, keys, or secrets associated with the deployment and review logs for signs of unauthenticated access. Until patched, restrict network exposure of the OnSight management interface to trusted networks only.

CVE-2026-84393 is an improper certificate validation flaw (CWE-297, host mismatch) in the ZTNA (Zero Trust Network Access) functionality of Fortinet FortiOS and FortiProxy, in which certificates are not correctly verified against the intended host. Per the related advisory headline, a network-adjacent or on-path attacker can exploit it to perform a man-in-the-middle attack against ZTNA connections, and the vendor describes the impact as information disclosure; the CVSS vector additionally rates confidentiality, integrity, and availability impact as high. Organizations running affected FortiOS 7.6.1 through 7.6.6 or FortiProxy 7.6.2 through 7.6.6 with ZTNA enabled are exposed. As of now there is no known exploitation, no public proof-of-concept, the flaw is not in CISA's KEV catalog, and EPSS puts 30-day exploitation probability at just 0.2% (5th percentile), so risk is currently low but patching is still warranted given the high CVSS score.

Do: Inventory FortiOS and FortiProxy deployments for versions 7.6.1–7.6.6 / 7.6.2–7.6.6 and prioritize upgrades to a fixed release listed in Fortinet's PSIRT advisory for this CVE (fixed versions are not specified in the available data). Until patched, treat ZTNA sessions on affected devices as susceptible to on-path interception and restrict or monitor ZTNA use, particularly for untrusted or public network paths. No public exploit or in-the-wild exploitation is known, so this can be handled in a normal patch cycle rather than emergency change.