CVE-2026-24858: Fortinet FortiAnalyzer Auth Bypass Flaw

CVE-2026-24858 Overview

CVE-2026-24858 is an Authentication Bypass Using an Alternate Path or Channel vulnerability (CWE-288) affecting multiple Fortinet products including FortiAnalyzer, FortiManager, FortiOS, FortiProxy, and FortiWeb. This critical vulnerability allows an attacker who possesses a valid FortiCloud account with a registered device to gain unauthorized access to other devices registered to different accounts when FortiCloud SSO authentication is enabled on those target devices.

The vulnerability exploits a flaw in the FortiCloud Single Sign-On (SSO) authentication mechanism, enabling cross-account device access that completely bypasses the intended account isolation. This represents a severe security boundary violation in Fortinet's cloud-integrated authentication infrastructure.

Critical Impact

Attackers with any valid FortiCloud account can potentially access and control Fortinet devices belonging to other organizations, leading to full device compromise, configuration theft, and network infrastructure takeover. This vulnerability is listed in CISA's Known Exploited Vulnerabilities catalog.

Affected Products

• Fortinet FortiAnalyzer versions 7.0.0-7.0.15, 7.2.0-7.2.11, 7.4.0-7.4.9, 7.6.0-7.6.5
• Fortinet FortiManager versions 7.0.0-7.0.15, 7.2.0-7.2.11, 7.4.0-7.4.9, 7.6.0-7.6.5
• Fortinet FortiOS versions 7.0.0-7.0.18, 7.2.0-7.2.12, 7.4.0-7.4.10, 7.6.0-7.6.5
• Fortinet FortiProxy versions 7.0.0-7.0.22, 7.2.0-7.2.15, 7.4.0-7.4.12, 7.6.0-7.6.4
• Fortinet FortiWeb versions 7.4.0-7.4.11, 7.6.0-7.6.6, 8.0.0-8.0.3

Discovery Timeline

• 2026-01-27 - CVE-2026-24858 published to NVD
• 2026-01-29 - Last updated in NVD database

Technical Details for CVE-2026-24858

Vulnerability Analysis

This vulnerability exists within the FortiCloud SSO authentication implementation across multiple Fortinet product lines. When FortiCloud SSO is enabled, devices authenticate users through Fortinet's cloud infrastructure. However, a flaw in the authentication validation logic fails to properly verify that the authenticating user's FortiCloud account is actually authorized to access the specific device being accessed.

The vulnerability allows an authenticated FortiCloud user to leverage their valid session credentials to authenticate against devices that are registered to completely separate FortiCloud accounts. This cross-account authentication bypass undermines the fundamental tenant isolation expected in cloud-managed security infrastructure.

The attack requires the attacker to have a legitimate FortiCloud account with at least one registered device. From this position, they can potentially enumerate and access other FortiCloud-managed devices that have SSO authentication enabled, regardless of account ownership.

Root Cause

The root cause of CVE-2026-24858 is improper validation during the FortiCloud SSO authentication flow. The affected products fail to adequately verify that the FortiCloud account initiating authentication is authorized to access the specific device being targeted. This represents a classic alternate path authentication bypass where the SSO mechanism trusts FortiCloud credentials without validating the account-to-device binding relationship.

Attack Vector

The attack is network-based and requires the attacker to have a valid FortiCloud account with at least one registered device. The exploitation flow involves:

1. Attacker creates or uses an existing FortiCloud account with a registered device
2. Attacker identifies target devices with FortiCloud SSO enabled (potentially through network scanning or reconnaissance)
3. Attacker initiates SSO authentication against target devices using their own FortiCloud credentials
4. Due to the validation flaw, the target device accepts the authentication despite the account mismatch
5. Attacker gains administrative access to devices belonging to other organizations

The vulnerability does not require user interaction and can be exploited remotely over the network. Once authenticated, attackers gain full administrative control over compromised devices, enabling configuration changes, credential theft, traffic interception, and further network compromise.

Detection Methods for CVE-2026-24858

Indicators of Compromise

• Unexpected FortiCloud SSO login events from unfamiliar source IPs or geographic locations
• Authentication logs showing successful SSO logins that don't correlate with legitimate administrator activity
• Multiple devices across different management domains showing authentication from the same FortiCloud account
• Configuration changes made by administrators not recognized by the organization

Detection Strategies

• Enable comprehensive authentication logging on all Fortinet devices and forward logs to a centralized SIEM solution
• Create correlation rules to detect SSO authentication events that don't match expected administrator accounts or access patterns
• Monitor for authentication attempts from FortiCloud accounts that are not explicitly authorized for your organization's devices
• Implement behavioral analytics to identify anomalous administrative access patterns

Monitoring Recommendations

• Review FortiCloud SSO authentication logs daily for any unauthorized access attempts
• Configure alerts for administrative logins occurring outside normal business hours or from unexpected locations
• Audit device configurations regularly for unauthorized changes that may indicate compromise
• Monitor network traffic for unusual communication patterns between Fortinet devices and external networks

How to Mitigate CVE-2026-24858

Immediate Actions Required

• Disable FortiCloud SSO authentication immediately on all affected devices if not strictly required
• Apply the latest security patches from Fortinet as soon as they become available
• Review authentication logs for signs of exploitation and investigate any suspicious SSO login events
• Implement network segmentation to limit the exposure of management interfaces

Patch Information

Fortinet has released security updates addressing this vulnerability. Organizations should consult the Fortinet PSIRT Advisory FG-IR-26-060 for specific patch versions and upgrade guidance. Given the critical severity and active exploitation status (CISA KEV listed), patching should be prioritized immediately.

Additional technical analysis is available in Fortinet's blog post on SSO abuse.

Workarounds

• Disable FortiCloud SSO authentication and switch to local authentication or alternative authentication methods until patches are applied
• Restrict network access to device management interfaces using firewall rules and access control lists
• Implement IP-based access restrictions to limit management access to known administrative networks only
• Enable multi-factor authentication for all administrative access where supported as an additional layer of defense

# Example: Disable FortiCloud SSO on FortiOS (apply appropriate commands for your device type)
config system global
    set forticloud-sso disable
end

# Restrict management access to specific trusted networks
config system interface
    edit "mgmt"
        set allowaccess ping https ssh
        set trusted-hosts 10.0.0.0/8 192.168.1.0/24
    next
end