CVE-2025-53843
📋 TL;DR
A stack-based buffer overflow vulnerability in Fortinet FortiOS allows attackers to execute arbitrary code via specially crafted packets. This affects FortiOS versions 7.6.0-7.6.3, 7.4.0-7.4.8, and all versions of 7.2, 7.0, and 6.4. Organizations using these vulnerable FortiOS versions on their FortiGate devices are at risk.
💻 Affected Systems
- Fortinet FortiOS
📦 What is this software?
Fortios by Fortinet
Fortios by Fortinet
⚠️ Risk & Real-World Impact
Worst Case
Complete system compromise with root-level access, enabling persistent backdoors, data exfiltration, and lateral movement across the network.
Likely Case
Remote code execution leading to service disruption, configuration changes, and potential credential theft from the FortiGate device.
If Mitigated
Limited impact if network segmentation, strict firewall rules, and intrusion prevention systems block malicious packets before reaching vulnerable interfaces.
🎯 Exploit Status
The vulnerability requires specially crafted packets but does not require authentication. Exploit development would require reverse engineering of the vulnerable packet processing code.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: FortiOS 7.6.4, 7.4.9, and later versions for affected branches
Vendor Advisory: https://fortiguard.fortinet.com/psirt/FG-IR-25-358
Restart Required: Yes
Instructions:
1. Log into FortiGate administrative interface. 2. Navigate to System > Firmware. 3. Download and install the patched firmware version (7.6.4, 7.4.9, or later). 4. Reboot the device after installation completes.
🔧 Temporary Workarounds
Restrict Network Access
allLimit which interfaces and IP addresses can send packets to the FortiGate management and data plane interfaces using firewall rules.
config firewall address
edit "TRUSTED_NETWORK"
set subnet 192.168.1.0 255.255.255.0
next
config firewall policy
edit 0
set srcintf "wan1"
set dstintf "internal"
set srcaddr "TRUSTED_NETWORK"
set dstaddr "all"
set action accept
set schedule "always"
set service "ALL"
next
🧯 If You Can't Patch
- Implement strict network segmentation to isolate FortiGate devices from untrusted networks.
- Enable and tune intrusion prevention system (IPS) signatures to detect and block buffer overflow attempts targeting FortiOS.
🔍 How to Verify
Check if Vulnerable:
Check FortiOS version via CLI: get system status | grep VersionCheck Version:
get system status | grep VersionVerify Fix Applied:
Verify installed version is 7.6.4, 7.4.9, or later: get system status | grep Version📡 Detection & Monitoring
Log Indicators:
- Unusual process creation events in FortiOS logs
- Multiple malformed packet rejection logs from the same source
Network Indicators:
- Spike in malformed packets to FortiGate interfaces
- Unusual outbound connections from FortiGate to external IPs
SIEM Query:
source="fortigate" AND (event_type="traffic" AND packet_size>1500) OR (event_type="system" AND message="*buffer*overflow*")