CVE-2026-24017: Fortinet FortiWeb Auth Bypass Vulnerability

CVE-2026-24017 Overview

An Improper Control of Interaction Frequency vulnerability (CWE-799) has been identified in Fortinet FortiWeb, a web application firewall product. This security flaw allows a remote unauthenticated attacker to bypass the authentication rate-limiting mechanism through specially crafted requests. By circumventing these protective controls, attackers can perform brute-force attacks against authentication endpoints without being throttled, potentially compromising user accounts and gaining unauthorized access to protected systems.

Critical Impact

Remote unauthenticated attackers can bypass authentication rate-limiting controls, enabling brute-force attacks against the FortiWeb management interface or protected applications. Attack success depends on attacker resources and target password complexity.

Affected Products

• Fortinet FortiWeb 8.0.0 through 8.0.2
• Fortinet FortiWeb 7.6.0 through 7.6.5
• Fortinet FortiWeb 7.4.0 through 7.4.10
• Fortinet FortiWeb 7.2.0 through 7.2.11
• Fortinet FortiWeb 7.0.0 through 7.0.11

Discovery Timeline

• 2026-03-10 - CVE-2026-24017 published to NVD
• 2026-03-12 - Last updated in NVD database

Technical Details for CVE-2026-24017

Vulnerability Analysis

This vulnerability stems from insufficient enforcement of rate-limiting controls on authentication endpoints within FortiWeb. The flaw allows attackers to craft requests in a manner that evades the frequency-based protections designed to prevent credential stuffing and brute-force attacks. The attack requires network access to the vulnerable FortiWeb appliance and does not require any prior authentication or user interaction.

While the attack complexity is considered high due to its dependence on attacker resources and the complexity of the target passwords, successful exploitation could result in complete compromise of confidentiality, integrity, and availability of the affected system. Attackers could potentially gain administrative access to the FortiWeb appliance, modify security policies, or access protected backend applications.

Root Cause

The vulnerability is classified under CWE-799 (Improper Control of Interaction Frequency), indicating that the rate-limiting implementation fails to properly track or enforce request frequency limitations. This could be due to insufficient session tracking, improper request counting mechanisms, or flaws in how the rate-limiter identifies and correlates requests from the same source.

Attack Vector

The attack is conducted over the network against the FortiWeb management interface or authentication endpoints. Attackers craft specially formatted requests that bypass the normal rate-limiting logic, allowing them to send authentication attempts at a higher frequency than intended. This enables efficient brute-force or credential stuffing attacks.

The vulnerability manifests in the authentication rate-limiting mechanism. Attackers can craft requests that evade the frequency-based controls, allowing rapid authentication attempts without triggering lockout protections. For technical implementation details, refer to the Fortinet Security Advisory FG-IR-26-082.

Detection Methods for CVE-2026-24017

Indicators of Compromise

• Unusually high volume of authentication attempts from single or multiple IP addresses
• Authentication failures followed by successful logins in rapid succession
• Request patterns with anomalous headers or formatting targeting authentication endpoints
• Log entries indicating multiple login attempts that bypass normal rate-limit triggers

Detection Strategies

• Monitor FortiWeb logs for abnormal authentication request patterns and volumes
• Implement network-level monitoring for high-frequency requests to authentication endpoints
• Deploy intrusion detection rules to identify rate-limit bypass attempt signatures
• Analyze authentication logs for successful logins following periods of multiple failures

Monitoring Recommendations

• Enable verbose logging on FortiWeb authentication components
• Configure SIEM alerts for authentication anomalies and suspicious request patterns
• Review access logs regularly for signs of brute-force activity
• Implement external rate-limiting at network perimeter as an additional control layer

How to Mitigate CVE-2026-24017

Immediate Actions Required

• Apply the latest FortiWeb firmware update as specified in the Fortinet advisory
• Restrict network access to FortiWeb management interfaces to trusted IP ranges only
• Implement strong password policies and enforce multi-factor authentication where possible
• Review authentication logs for signs of prior exploitation attempts

Patch Information

Fortinet has released security updates to address this vulnerability. Administrators should upgrade to the latest patched version of FortiWeb for their respective branch. Consult the Fortinet Security Advisory FG-IR-26-082 for specific version requirements and download links.

Workarounds

• Restrict management interface access to trusted internal networks or VPN connections only
• Implement additional network-level rate-limiting using upstream firewalls or load balancers
• Enable account lockout policies with appropriate thresholds
• Consider deploying additional authentication controls such as CAPTCHA or MFA

# Example: Restrict FortiWeb management access via firewall rule
# Limit access to trusted administrative subnet only
config firewall policy
    edit 1
        set srcintf "wan1"
        set dstintf "mgmt"
        set srcaddr "trusted-admin-subnet"
        set dstaddr "fortiweb-mgmt"
        set action accept
        set schedule "always"
        set service "HTTPS"
    next
end