{"id":231704,"date":"2026-04-21T15:15:34","date_gmt":"2026-04-21T15:15:34","guid":{"rendered":"https:\/\/www.intrinsec.com\/?p=231704"},"modified":"2026-04-22T08:27:28","modified_gmt":"2026-04-22T08:27:28","slug":"fortinet-fsso-is-lying-to-you","status":"publish","type":"post","link":"https:\/\/www.intrinsec.com\/en\/fortinet-fsso-is-lying-to-you\/","title":{"rendered":"Fortinet FSSO is lying to you"},"content":{"rendered":"<div data-elementor-type=\"wp-post\" data-elementor-id=\"231704\" class=\"elementor elementor-231704\" data-elementor-settings=\"{&quot;element_pack_global_tooltip_width&quot;:{&quot;unit&quot;:&quot;px&quot;,&quot;size&quot;:&quot;&quot;,&quot;sizes&quot;:[]},&quot;element_pack_global_tooltip_width_tablet&quot;:{&quot;unit&quot;:&quot;px&quot;,&quot;size&quot;:&quot;&quot;,&quot;sizes&quot;:[]},&quot;element_pack_global_tooltip_width_mobile&quot;:{&quot;unit&quot;:&quot;px&quot;,&quot;size&quot;:&quot;&quot;,&quot;sizes&quot;:[]},&quot;element_pack_global_tooltip_padding&quot;:{&quot;unit&quot;:&quot;px&quot;,&quot;top&quot;:&quot;&quot;,&quot;right&quot;:&quot;&quot;,&quot;bottom&quot;:&quot;&quot;,&quot;left&quot;:&quot;&quot;,&quot;isLinked&quot;:true},&quot;element_pack_global_tooltip_padding_tablet&quot;:{&quot;unit&quot;:&quot;px&quot;,&quot;top&quot;:&quot;&quot;,&quot;right&quot;:&quot;&quot;,&quot;bottom&quot;:&quot;&quot;,&quot;left&quot;:&quot;&quot;,&quot;isLinked&quot;:true},&quot;element_pack_global_tooltip_padding_mobile&quot;:{&quot;unit&quot;:&quot;px&quot;,&quot;top&quot;:&quot;&quot;,&quot;right&quot;:&quot;&quot;,&quot;bottom&quot;:&quot;&quot;,&quot;left&quot;:&quot;&quot;,&quot;isLinked&quot;:true},&quot;element_pack_global_tooltip_border_radius&quot;:{&quot;unit&quot;:&quot;px&quot;,&quot;top&quot;:&quot;&quot;,&quot;right&quot;:&quot;&quot;,&quot;bottom&quot;:&quot;&quot;,&quot;left&quot;:&quot;&quot;,&quot;isLinked&quot;:true},&quot;element_pack_global_tooltip_border_radius_tablet&quot;:{&quot;unit&quot;:&quot;px&quot;,&quot;top&quot;:&quot;&quot;,&quot;right&quot;:&quot;&quot;,&quot;bottom&quot;:&quot;&quot;,&quot;left&quot;:&quot;&quot;,&quot;isLinked&quot;:true},&quot;element_pack_global_tooltip_border_radius_mobile&quot;:{&quot;unit&quot;:&quot;px&quot;,&quot;top&quot;:&quot;&quot;,&quot;right&quot;:&quot;&quot;,&quot;bottom&quot;:&quot;&quot;,&quot;left&quot;:&quot;&quot;,&quot;isLinked&quot;:true}}\" data-elementor-post-type=\"post\">\n\t\t\t\t<div class=\"elementor-element elementor-element-b9b6c0f e-flex e-con-boxed e-con e-parent\" data-id=\"b9b6c0f\" data-element_type=\"container\" data-e-type=\"container\">\n\t\t\t\t\t<div class=\"e-con-inner\">\n\t\t\t\t<div class=\"elementor-element elementor-element-74a893c elementor-widget elementor-widget-text-editor\" data-id=\"74a893c\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"text-editor.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t\t\t\t\t\t\t<p dir=\"auto\" data-sourcepos=\"3:1-3:254\">During a recent investigation, <strong>Intrinsic CERT<\/strong> encountered an issue where <strong>Fortinet FSSO logs\u00a0<\/strong>were<strong> wrongfully attributing malicious traffic<\/strong> performed through the VPN <strong>to an unrelated user<\/strong> instead of the compromised account linked to the IP address used for this traffic.<\/p><p dir=\"auto\" data-sourcepos=\"5:1-5:129\">This article aims to warn you about this issue, as to not blindly trust FortiGate logs during your digital forensics analysis.<\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-ac731d4 elementor-widget elementor-widget-heading\" data-id=\"ac731d4\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"heading.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t\t\t<h2 class=\"elementor-heading-title elementor-size-default\">What is Fortinet FSSO?<\/h2>\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-78df5d1 elementor-widget elementor-widget-text-editor\" data-id=\"78df5d1\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"text-editor.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t\t\t\t\t\t\t<p><strong>Fortinet FSSO<\/strong> (<em>Fortinet Single Sign-On<\/em>) is a feature that enables Fortinet security appliances, such as FortiGate firewalls, to <strong>identify network users based on their Active Directory credentials<\/strong> without requiring repeated logins or additional authentication prompts when accessing resources.<\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-685b2e7 elementor-widget elementor-widget-heading\" data-id=\"685b2e7\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"heading.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t\t\t<h2 class=\"elementor-heading-title elementor-size-default\">How does Fortinet FSSO work?<\/h2>\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t<div class=\"elementor-element elementor-element-9cfdbd0 e-flex e-con-boxed e-con e-parent\" data-id=\"9cfdbd0\" data-element_type=\"container\" data-e-type=\"container\">\n\t\t\t\t\t<div class=\"e-con-inner\">\n\t\t\t\t<div class=\"elementor-element elementor-element-54a7c91 elementor-widget elementor-widget-text-editor\" data-id=\"54a7c91\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"text-editor.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t\t\t\t\t\t\t<ol><li data-sourcepos=\"13:1-13:75\">The FSSO Agent monitors the authentication events on domain controllers.<\/li><li data-sourcepos=\"14:1-14:140\"><strong data-sourcepos=\"14:4-14:41\">When a user logs in to the network<\/strong> (eg, through a Windows domain login), the agent collects the username and the user&#039;s IP address.<\/li><li data-sourcepos=\"15:1-15:62\">The agent sends this information to the FortiGate firewall.<\/li><li data-sourcepos=\"16:1-17:0\">Firewall policies on the FortiGate can now be applied using user or group identity (instead of source IP only), allowing for more granular, role-based security controls.<\/li><\/ol>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-0dcc712 elementor-widget elementor-widget-heading\" data-id=\"0dcc712\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"heading.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t\t\t<h2 class=\"elementor-heading-title elementor-size-default\">Incorrect username\/IP mapping with remote connections<\/h2>\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t<div class=\"elementor-element elementor-element-5ee49d4 e-flex e-con-boxed e-con e-parent\" data-id=\"5ee49d4\" data-element_type=\"container\" data-e-type=\"container\">\n\t\t\t\t\t<div class=\"e-con-inner\">\n\t\t\t\t<div class=\"elementor-element elementor-element-60ec319 elementor-widget elementor-widget-text-editor\" data-id=\"60ec319\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"text-editor.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t\t\t\t\t\t\t<p>In VPN scenarios, dynamic IP assignment complicates reliable user\/IP mapping.<\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-2c06dfd elementor-widget elementor-widget-heading\" data-id=\"2c06dfd\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"heading.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t\t\t<h3 class=\"elementor-heading-title elementor-size-default\">Why?<\/h3>\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-6edce52 elementor-widget elementor-widget-text-editor\" data-id=\"6edce52\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"text-editor.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t\t\t\t\t\t\t<ul dir=\"auto\" data-sourcepos=\"24:1-26:84\"><li data-sourcepos=\"24:1-24:90\">When a user connects through the VPN, a new (virtual) IP address is assigned to their session.<\/li><li data-sourcepos=\"25:1-25:127\">As IP addresses assignment is dynamic, when two users connect to the VPN non-concurrently, the same IP address from the VPN pool might be reused.<\/li><li data-sourcepos=\"26:1-26:84\">It seems that <strong>the FSSO agent does not update its username\/IP mapping in that case<\/strong>.<\/li><\/ul><p dir=\"auto\" data-sourcepos=\"28:1-28:100\">The result is <strong>an outdated, incorrect or completely missing username\/IP mapping for VPN-assigned IPs<\/strong>.<\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-01ebe89 elementor-widget elementor-widget-heading\" data-id=\"01ebe89\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"heading.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t\t\t<h3 class=\"elementor-heading-title elementor-size-default\">Real-World Example<\/h3>\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-4520796 elementor-widget elementor-widget-text-editor\" data-id=\"4520796\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"text-editor.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t\t\t\t\t\t\t<p dir=\"auto\" data-sourcepos=\"32:1-32:62\">During our investigations, we identified the following events:<\/p><ol dir=\"auto\" data-sourcepos=\"34:1-35:91\"><li data-sourcepos=\"34:1-34:357\">A malicious actor initiated a VPN connection via stolen credentials of user <strong>XXX<\/strong> and gets attributed the IP address <strong>172.16.10.1<\/strong> inside the network while no multi-factor authentication mechanism was set up. (see also our previous article for <a href=\"https:\/\/www.intrinsec.com\/en\/vpn-compromises-real-word-use-cases\/\" target=\"_blank\" rel=\"nofollow noreferrer noopener\" data-sourcepos=\"34:244-34:356\">5 real-world scenarios involving compromised VPNs<\/a>)<\/li><li data-sourcepos=\"35:1-35:91\">The attacker then performed a <strong>SMB scan<\/strong> of the internal network using the IP <strong>172.16.10.1<\/strong>.<\/li><\/ol><p dir=\"auto\" data-sourcepos=\"37:1-37:44\">In the different logs sources, we observed:<\/p><ul dir=\"auto\" data-sourcepos=\"39:1-41:92\"><li data-sourcepos=\"39:1-39:109\">In the <strong>VPN logs<\/strong>, that the malicious session lasted from <strong>2026-01-15 14:40:05<\/strong> UTC to <strong>2026-01-15 15:20:58<\/strong> UTC.<\/li><li data-sourcepos=\"40:1-40:133\">In the <strong>FortiGate logs<\/strong>, traffic where <code data-sourcepos=\"40:39-40:45\">script<\/code> is <strong>172.16.10.1<\/strong> and <code data-sourcepos=\"40:66-40:74\">dstport<\/code> is 445 during the time frame of the malicious VPN sessions.<\/li><li data-sourcepos=\"41:1-41:92\">In the <strong>Windows event logs<\/strong>, events 5140 during the time frame of the malicious VPN sessions.<\/li><\/ul><p dir=\"auto\" data-sourcepos=\"43:1-43:258\">In the <strong>FortiGate FSSO logs<\/strong>, however, we spotted an inconsistency where there was <strong>no SMB traffic involving user XXX during the malicious VPN session<\/strong>. Even worse, the corresponding <strong>SMB traffic was attributed to user YYY<\/strong> who was not in our list of compromised accounts.<\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-74c8599 elementor-widget elementor-widget-image\" data-id=\"74c8599\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"image.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t<img fetchpriority=\"high\" decoding=\"async\" width=\"1000\" height=\"653\" src=\"https:\/\/www.intrinsec.com\/wp-content\/uploads\/2026\/04\/schema_fsso-1024x669.png\" class=\"attachment-large size-large wp-image-231725\" alt=\"Schema FSSO\" srcset=\"https:\/\/www.intrinsec.com\/wp-content\/uploads\/2026\/04\/schema_fsso-1024x669.png 1024w, https:\/\/www.intrinsec.com\/wp-content\/uploads\/2026\/04\/schema_fsso-300x196.png 300w, https:\/\/www.intrinsec.com\/wp-content\/uploads\/2026\/04\/schema_fsso-768x502.png 768w, https:\/\/www.intrinsec.com\/wp-content\/uploads\/2026\/04\/schema_fsso-1536x1004.png 1536w, https:\/\/www.intrinsec.com\/wp-content\/uploads\/2026\/04\/schema_fsso-2048x1338.png 2048w, https:\/\/www.intrinsec.com\/wp-content\/uploads\/2026\/04\/schema_fsso-18x12.png 18w, https:\/\/www.intrinsec.com\/wp-content\/uploads\/2026\/04\/schema_fsso-650x425.png 650w\" sizes=\"(max-width: 1000px) 100vw, 1000px\" \/>\t\t\t\t\t\t\t\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-e23195c elementor-widget elementor-widget-text-editor\" data-id=\"e23195c\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"text-editor.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t\t\t\t\t\t\t<p>That is why it is very important, during forensics analysis, to <strong>consolidate events with different log sources<\/strong> and to avoid trusting, without verification, computed fields provided by security vendors.<\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-1580278 elementor-widget elementor-widget-heading\" data-id=\"1580278\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"heading.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t\t\t<h2 class=\"elementor-heading-title elementor-size-default\">Conclusion<\/h2>\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-5add6ed elementor-widget elementor-widget-text-editor\" data-id=\"5add6ed\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"text-editor.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t\t\t\t\t\t\t<p dir=\"auto\" data-sourcepos=\"49:1-49:346\"><strong>Fortinet&#039;s FSSO solution is a powerful tool<\/strong> for automating authentication and identity-aware security policies.<\/p><p dir=\"auto\" data-sourcepos=\"49:1-49:346\">However, its user\/IP mapping <strong>has clear limitations in VPN contexts<\/strong>, since there isn&#039;t a corresponding Active Directory authentication event. This \u201cgray area\u201d creates <strong>attribution errors with direct impact on incident response and forensic analysis<\/strong>.<\/p><p dir=\"auto\" data-sourcepos=\"51:1-51:95\">Adapting your monitoring and logging strategy is essential to compensate for these limitations.<\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-c0fc7d8 elementor-widget elementor-widget-heading\" data-id=\"c0fc7d8\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"heading.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t\t\t<h2 class=\"elementor-heading-title elementor-size-default\">About us<\/h2>\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-8b2f2dc elementor-widget elementor-widget-text-editor\" data-id=\"8b2f2dc\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"text-editor.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t\t\t\t\t\t\t<p>CERT Intrinsec is the incident response and cybersecurity research team of Intrinsec. We specialize in digital forensics, threat hunting, and incident response for complex security incidents across enterprise environments.<\/p><p>Our mission is to investigate real-world intrusions, expose technical blind spots, and help organizations strengthen their detection and response capabilities through actionable research and field experience.<\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-9504ea6 elementor-widget elementor-widget-button\" data-id=\"9504ea6\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"button.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t\t\t\t\t\t\t<div class=\"elementor-button-wrapper\">\n\t\t\t\t\t<a class=\"elementor-button elementor-button-link elementor-size-sm\" href=\"\/en\/gestion-de-crise-cyber\/\">\n\t\t\t\t\t\t<span class=\"elementor-button-content-wrapper\">\n\t\t\t\t\t\t\t\t\t<span class=\"elementor-button-text\">More information<\/span>\n\t\t\t\t\t<\/span>\n\t\t\t\t\t<\/a>\n\t\t\t\t<\/div>\n\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t<div class=\"elementor-element elementor-element-7f0f628 e-flex e-con-boxed e-con e-parent\" data-id=\"7f0f628\" data-element_type=\"container\" data-e-type=\"container\">\n\t\t\t\t\t<div class=\"e-con-inner\">\n\t\t\t\t<div class=\"elementor-element elementor-element-a4356c2 elementor-widget-divider--view-line elementor-widget elementor-widget-divider\" data-id=\"a4356c2\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"divider.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t\t\t\t\t<div class=\"elementor-divider\">\n\t\t\t<span class=\"elementor-divider-separator\">\n\t\t\t\t\t\t<\/span>\n\t\t<\/div>\n\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-4377e75 elementor-widget elementor-widget-heading\" data-id=\"4377e75\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"heading.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t\t\t<h3 class=\"elementor-heading-title elementor-size-default\">Sources<\/h3>\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<div class=\"elementor-element elementor-element-c711b86 elementor-widget elementor-widget-text-editor\" data-id=\"c711b86\" data-element_type=\"widget\" data-e-type=\"widget\" data-widget_type=\"text-editor.default\">\n\t\t\t\t<div class=\"elementor-widget-container\">\n\t\t\t\t\t\t\t\t\t<p><a href=\"https:\/\/docs.fortinet.com\/document\/fortigate\/7.6.5\/administration-guide\/450337\/fsso\">Fortinet FSSO<\/a><\/p>\t\t\t\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t<div class=\"elementor-element elementor-element-1fe9f5b e-flex e-con-boxed e-con e-parent\" data-id=\"1fe9f5b\" data-element_type=\"container\" data-e-type=\"container\">\n\t\t\t\t\t<div class=\"e-con-inner\">\n\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t<div class=\"elementor-element elementor-element-f14a504 e-flex e-con-boxed e-con e-parent\" data-id=\"f14a504\" data-element_type=\"container\" data-e-type=\"container\">\n\t\t\t\t\t<div class=\"e-con-inner\">\n\t\t\t\t\t<\/div>\n\t\t\t\t<\/div>\n\t\t\t\t<\/div>","protected":false},"excerpt":{"rendered":"<p>During a recent investigation, CERT Intrinsec encountered an issue where Fortinet FSSO logs were wrongfully attributing a username\/IP address to malicious traffic inside the company&#039;s network while the initiating connection was performed through the VPN.<br \/>\nThis article aims to warn you about this issue, as to not blindly trust FortiGate logs during your digital forensics analysis.<\/p>","protected":false},"author":55,"featured_media":231742,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[6],"tags":[176],"class_list":["post-231704","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-cert","tag-incident-response"],"yoast_head":"<!-- This site is optimized with the Yoast SEO Premium plugin v28.0 (Yoast SEO v28.1) - 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