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FortiOS and FortiProxy ZTNA Validation Vulnerability Allows Attacker to Perform a Man-in-the-Middle Attack

Fortinet discloses high-severity certificate validation flaw CVE-2026-84393 in FortiOS and FortiProxy Agentless ZTNA portals enabling unauthenticated man-in-the-middle attacks.

Fortinet disclosed CVE-2026-84393 (CVSSv3 7.3, CWE-295) on September 8, 2026 under advisory FG-IR-26-174: improper certificate validation in the Agentless ZTNA portal of FortiOS and FortiProxy. An unauthenticated attacker on the network path could present a forged or mismatched certificate and intercept or tamper with traffic between the portal and backend destinations, with impact classified as information disclosure. Affected versions are FortiOS 7.6.1 through 7.6.6 and FortiProxy 7.6.2 through 7.6.6; the 8.0, 7.4 and 7.2 branches of both products are unaffected. Fortinet urges upgrading to 7.6.7 or later and reports no evidence of exploitation in the wild.

Gunra Ransomware Exploits Fortinet FortiOS, FortiProxy Flaws to Breach Networks

CISA, FBI, and South Korean agencies warn Gunra ransomware, with 51 victims since April 2025, exploits Fortinet flaws for double-extortion attacks on critical infrastructure.

CISA, the FBI, and South Korean agencies warned of Gunra ransomware attacks targeting healthcare, financial services, government, and professional services worldwide. The Conti-derived operation exploits internet-facing Fortinet FortiOS and FortiProxy flaws CVE-2024-55591 and CVE-2025-24472 for initial access, then deploys double extortion with Salsa20/ChaCha20 encryption and publishes non-payers on a leak site within five to seven days. Ransomware.Live lists 51 victims since April 2025, mostly in South Korea, Brazil, Spain, Thailand, and Hong Kong. The group uses Impacket tools for SMB lateral movement and NTDS credential dumping, tampers with VDI authentication to accept a designated OTP value to bypass MFA, and launched a RaaS affiliate program in January 2026 under the new alias Golden Community.

The Hacker News · Aug 12, 2026Ransomware in the wildCVE-2024-55591CVE-2025-24472

ZTNA Portal Improper Certificate Validation

Fortinet fixed an improper certificate validation flaw (CVSS 7.3) in FortiOS and FortiProxy Agentless ZTNA portal enabling unauthenticated man-in-the-middle attacks on backend traffic.

Fortinet advisory FG-IR-26-174 discloses an improper certificate validation vulnerability (CWE-295) in the FortiOS and FortiProxy Agentless ZTNA portal, rated CVSSv3 7.3. A remote and unauthenticated attacker can perform a man-in-the-middle attack on the communication channel between the ZTNA portal and the backend destination website. The advisory was revised on 2026-09-08.

Fortinet PSIRT · 8d agoAdvisory

Fortinet Patches Critical Vulnerabilities in FortiMonitorOnSight, Chrome Extension

Fortinet patched 10 vulnerabilities including two critical authentication flaws, CVE-2026-84390 (CVSS 9.6) and CVE-2026-84388 (CVSS 9.1), in FortiMonitorOnSight and the FortiPAM Chrome extension.

Fortinet's September patch release fixes CVE-2026-84390, a sensitive-information issue in the FortiMonitorOnSight web portal that lets unauthenticated attackers bypass authentication with forged or reused JWTs. CVE-2026-84388 is an improper authentication flaw in the Fortinet Privileged Access Agent Chrome extension that can allow attackers to proxy a user's browser traffic via a malicious website, requiring upgrades to both FortiPAM 1.9.1/1.8.4 and extension 8.0.1.123+. High-severity information disclosure in FortiSandbox (CVE-2026-26084) and man-in-the-middle risk in the FortiOS/FortiProxy Agentless ZTNA portal (CVE-2026-84393) were also fixed, alongside medium/low issues across FortiManager, FortiAnalyzer, FortiSOAR, FortiClient, FortiSIEM and others. Fortinet did not indicate any of the flaws are being exploited in the wild.

August 2026 CVE Landscape

Insikt Group catalogs 73 high-impact August 2026 CVEs (43 Very Critical), including PaperCut, Zimbra, and Metabase flaws actively exploited or weaponized.

Recorded Future's Insikt Group identified 73 high-impact vulnerabilities in August 2026, 43 rated Very Critical, spanning 45 vendors with Microsoft accounting for roughly 11%. 31 vulnerabilities surfaced via CISA's KEV catalog, with others validated via open sources, vendor telemetry, and honeypot data. New Nuclei detection templates were released for CVE-2025-62593 (Ray), CVE-2026-72898 (Metabase), and CVE-2026-9198 (IBM Langflow). The report also highlights two AI-assisted operations: UAT-10147 exploited Zimbra, AjaxPro, Nacos, and Telerik servers before using DeepAudit and PentestGPT post-compromise, while a separate Chinese-speaking actor weaponized Hermes Agent and DeepSeek in a failed attempt.

Recorded Future · 8d agoVulnerability in the wildCVE-2025-62593CVE-2026-72898CVE-2026-9198+4 CVEs1