CVE-2025-55018
📋 TL;DR
This HTTP request smuggling vulnerability in Fortinet FortiOS allows unauthenticated attackers to bypass firewall policies by sending specially crafted HTTP headers. Affected systems include FortiOS versions 7.6.0, 7.4.0-7.4.9, all 7.2 and 7.0 versions, and 6.4.3-6.4.16.
💻 Affected Systems
- Fortinet FortiOS
📦 What is this software?
Fortios by Fortinet
Fortios by Fortinet
Fortios by Fortinet
⚠️ Risk & Real-World Impact
Worst Case
Attackers could smuggle malicious HTTP requests past firewall policies, potentially enabling web application attacks, data exfiltration, or lateral movement within the network.
Likely Case
Attackers bypass firewall rules to access restricted web resources or services that should be blocked, potentially leading to information disclosure or unauthorized access.
If Mitigated
With proper network segmentation and additional security controls, impact is limited to potential policy bypass without direct system compromise.
🎯 Exploit Status
Exploitation requires crafting specific HTTP headers to trigger inconsistent parsing between FortiOS components.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: FortiOS 7.6.1, 7.4.10, 7.2.8, 7.0.15, 6.4.17
Vendor Advisory: https://fortiguard.fortinet.com/psirt/FG-IR-25-667
Restart Required: Yes
Instructions:
1. Download the appropriate firmware update from Fortinet support portal. 2. Backup current configuration. 3. Apply firmware update following Fortinet upgrade procedures. 4. Reboot the device. 5. Verify the new version is running.
🔧 Temporary Workarounds
Disable HTTP/HTTPS inspection
fortiosTemporarily disable HTTP/HTTPS inspection on affected firewall policies to prevent exploitation
config firewall policy
edit <policy_id>
unset inspection-mode
next
end
🧯 If You Can't Patch
- Implement network segmentation to isolate vulnerable devices from critical assets
- Deploy additional web application firewall (WAF) in front of FortiOS devices
🔍 How to Verify
Check if Vulnerable:
Check FortiOS version via CLI: 'get system status' and compare against affected versionsCheck Version:
get system status | grep VersionVerify Fix Applied:
After patching, verify version is updated to patched versions: 7.6.1, 7.4.10, 7.2.8, 7.0.15, or 6.4.17📡 Detection & Monitoring
Log Indicators:
- Unusual HTTP header patterns in firewall logs
- HTTP requests bypassing expected policies
Network Indicators:
- HTTP traffic with malformed or unusual headers
- Requests reaching backend servers that should be blocked
SIEM Query:
source="fortigate" AND (http_header contains "transfer-encoding" OR http_header contains "content-length") AND http_header matches abnormal patterns