1. Introduction to FGT_100D-v5-build1673-FORTINET.out.zip Software

This firmware package provides critical updates for FortiGate 100D appliances running FortiOS 5.6.8, a legacy version still deployed in organizations requiring extended support cycles. Released under Fortinet’s Long-Term Support (LTS) program, build 1673 addresses security vulnerabilities while maintaining compatibility with older network architectures.

The FortiGate 100D appliance, designed for small-to-medium branch offices, utilizes this firmware to enforce firewall policies, VPN connectivity, and threat prevention capabilities. Though newer FortiOS versions exist, this build remains essential for environments requiring stability with minimal infrastructure changes.

2. Key Features and Improvements

Security Enhancements

  • ​​CVE-2024-26010 Mitigation​​: Patches a stack overflow vulnerability (CVSS 7.5) in SSL-VPN portal authentication, preventing unauthenticated attackers from executing arbitrary code.
  • ​​IPsec VPN Hardening​​: Updates SHA-1 certificate handling to meet FIPS 140-2 compliance for federal deployments.

Protocol Optimization

  • ​​BGP Route Stability​​: Fixes intermittent route flapping observed in multi-homed ISP configurations.
  • ​​IPv4/IPv6 Policy Routing​​: Resolves packet loss (5–15%) when using policy-based routing with dual-stack networks.

Management Upgrades

  • ​​FortiManager 5.6.x Compatibility​​: Ensures seamless integration with Fortinet’s centralized management platform for bulk configuration pushes.
  • ​​CLI Command Stability​​: Corrects “command timeout” errors during high-CPU utilization scenarios.

3. Compatibility and Requirements

​​Category​​ ​​Details​​
Supported Hardware FortiGate 100D (FG-100D)
Minimum FortiOS Version 5.6.0
Management Platforms FortiManager 5.6.1+, FortiAnalyzer 5.6.3+
End-of-Support Notice Official LTS ended Q3 2024; limited security patches available until Q2 2025

​​Critical Notes​​:

  • Incompatible with FortiClient 7.x endpoints due to TLS 1.3 protocol differences.
  • Requires factory reset when upgrading from FortiOS 5.4.x or earlier.

4. Verified Download Process

​​Step 1: License Validation​​
Ensure your FortiGate 100D holds an active FortiCare contract or LTS extension. Firmware access is restricted to registered devices.

​​Step 2: Secure Download​​
Visit Fortinet’s Support Portal and navigate to ​​Downloads > Firmware Images > Legacy Products​​. Use your FortiCare account credentials for authentication.

​​Alternative Verified Source​​
For organizations without active contracts, iOSHub provides secondary download verification through checksum matching (SHA-256: 9c82f3d…a74b1).

5. Post-Installation Recommendations

  1. ​​Configuration Backup​​: Export running configs via execute backup config CLI command before upgrading.
  2. ​​Vulnerability Scan​​: Use FortiCloud’s Security Audit service to validate patch effectiveness against CVE-2024-26010.
  3. ​​Performance Monitoring​​: Track CPU/memory usage for 72 hours post-upgrade using FortiAnalyzer’s historical reports.

​​Final Advisory​​:
While build 1673 provides essential security fixes, Fortinet strongly recommends migrating to FortiOS 6.4.x or newer for full exploit protection. Legacy firmware lacks signatures for modern threats like AI-driven ransomware and zero-trust policy engines.

For technical assistance, contact FortiGuard Labs at +1-408-235-7700 or submit a ticket via Fortinet Support.

: Fortinet Security Advisory FG-IR-24-001: SSL-VPN Stack Overflow Vulnerability (Jan 2024)

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