Fortinet FortiOS and Multi-Product FortiCloud SSO Authentication Bypass Vulnerability (CVE-2026-24858) Critical Security Advisory
Executive & SecOps Summary
SECOPS ASSESSMENTFortiOS, FortiManager, FortiAnalyzer, FortiProxy, FortiWeb, and FortiNAC-F devices with FortiCloud SSO authentication enabled
An attacker with a valid FortiCloud account and a registered device can bypass authentication to log into other registered devices under different accounts, gaining full administrative control (CVSS 9.8, Active KEV)
Immediately upgrade to the patched firmware versions or disable FortiCloud SSO administrator login on all affected devices
Affected Products & Version Scope
Remediation & Live Workaround Commands
PATCH & WORKAROUND1. Official Patch & Version Upgrade Commands
Immediately upgrade to the patched firmware versions recommended by Fortinet. Verify your current version and perform the upgrade via the CLI.
# Check current system status and firmware version
get system status
# Restore/Upgrade firmware image via TFTP (Example for FortiOS)
# Note: Ensure you use the correct patched image version (e.g., 7.4.11+, 7.2.13+, etc.)
execute restore image tftp <firmware_image_name> <tftp_server_ip>2. Temporary Workaround & Hardening Configuration
If patching cannot be applied immediately, disable FortiCloud SSO administrator login via the CLI to mitigate the attack vector.
# Disable FortiCloud SSO login options in FortiOS
config system admin setting
set admin-login-adom-sso disable
set admin-forticloud-sso-login disable
end
# Restrict administrative access using Trusted Hosts
config system admin
edit 'admin'
set trusthost1 192.168.10.0 255.255.255.0
set trusthost2 10.10.0.0 255.255.0.0
next
end3. Log Audit & IoC Verification Commands
Audit system event logs to detect unauthorized SSO login attempts or successful bypasses.
# Configure log filters to display system event logs
show log disk filter
set category event
set severity information
end
# Filter and display logs containing 'sso' or 'login' actions
execute log filter category 1
execute log filter field action login
execute log display | grep -i 'sso'Block Exploits Instantly with Managed Virtual Patching Rules
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Technical Root Cause & Exploitation Mechanics
1. Vulnerability Overview & Root Cause
This vulnerability (CVE-2026-24858) is an Authentication Bypass Using an Alternate Path or Channel [CWE-288] within Fortinet's FortiCloud SSO (Single Sign-On) authentication mechanism. The root cause lies in a logical flaw during the validation of authentication tokens and requests received by the device, where the system fails to strictly isolate and verify the tenant or account boundaries of the requesting entity.
2. Exploitation Mechanics & Attack Scenario
To exploit this vulnerability, an attacker must possess a valid FortiCloud account and at least one registered Fortinet device. The attacker targets a device that has FortiCloud SSO authentication enabled. By crafting and manipulating authentication requests using their own FortiCloud session and registered device context, the attacker routes the request to the target device belonging to a different account. Because the SSO module fails to validate the account ownership boundary, it accepts the alternate path authentication as valid, granting the attacker unauthorized administrative access.
3. Infrastructure & Business Impact
With a CVSS score of 9.8, this vulnerability poses a critical threat and has been actively exploited in the wild, leading to its inclusion in the CISA KEV catalog. Successful exploitation allows remote attackers to compromise core security and network infrastructure (firewalls, log analyzers, and management consoles). This can result in complete network compromise, unauthorized traffic interception, disabling of security policies, lateral movement, and sensitive data exfiltration.
Official Vendor Advisories & References
An Authentication Bypass Using an Alternate Path or Channel vulnerability [CWE-288] vulnerability in Fortinet FortiAnalyzer 7.6.0 through 7.6.5, FortiAnalyzer 7.4.0 through 7.4.9, FortiAnalyzer 7.2.0 through 7.2.11, FortiAnalyzer 7.0.0 through 7.0.15, FortiManager 7.6.0 through 7.6.5, FortiManager 7.4.0 through 7.4.9, FortiManager 7.2.0 through 7.2.11, FortiManager 7.0.0 through 7.0.15, FortiNAC-F 7.6.3 through 7.6.5, FortiOS 7.6.0 through 7.6.5, FortiOS 7.4.0 through 7.4.10, FortiOS 7.2.0 through 7.2.12, FortiOS 7.0.0 through 7.0.18, FortiProxy 7.6.0 through 7.6.4, FortiProxy 7.4.0 through 7.4.12, FortiProxy 7.2.0 through 7.2.15, FortiProxy 7.0.0 through 7.0.22, FortiWeb 8.0.0 through 8.0.3, FortiWeb 7.6.0 through 7.6.6, FortiWeb 7.4.0 through 7.4.11 may allow an attacker with a FortiCloud account and a registered device to log into other devices registered to other accounts, if FortiCloud SSO authentication is enabled on those devices.
Frequently Asked SecOps Questions (CVE-2026-24858)
FAQQ1. How critical is CVE-2026-24858 and is it actively exploited in the wild?
CVE-2026-24858 is rated CVSS 9.8 (CRITICAL) with a 30-day EPSS exploitation probability of 86.6%. It is listed in the CISA Known Exploited Vulnerabilities (KEV) catalog, requiring immediate emergency remediation.
Q2. Which vendors and products are affected by CVE-2026-24858?
Primary impacted vendors include fortinet across fortios, fortimanager, fortianalyzer, fortiproxy, fortiweb, fortinac-f. Scope summary: Affected versions with FortiCloud SSO enabled: - FortiOS: 7.6.0 to 7.6.5, 7.4.0 to 7.4.10, 7.2.0 to 7.2.12, 7.0.0 to 7.0.18 - FortiManager: 7.6.0 to 7.6.5, 7.4.0 to 7.4.9, 7.2.0 to 7.2.11, 7.0.0 to 7.0.15 - FortiAnalyzer: 7.6.0 to 7.6.5, 7.4.0 to 7.4.9, 7.2.0 to 7.2.11, 7.0.0 to 7.0.15 - FortiProxy: 7.6.0 to 7.6.4, 7.4.0 to 7.4.12, 7.2.0 to 7.2.15, 7.0.0 to 7.0.22 - FortiWeb: 8.0.0 to 8.0.3, 7.6.0 to 7.6.6, 7.4.0 to 7.4.11 - FortiNAC-F: 7.6.3 to 7.6.5
Q3. What temporary mitigations or workarounds exist for CVE-2026-24858 before patching?
[Mitigation] Immediately upgrade to the patched firmware versions or disable FortiCloud SSO administrator login on all affected devices Follow the CLI remediation commands and interactive SecOps checklist on this page to restrict exposure prior to your maintenance window.
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