CVE-2024-20407
📋 TL;DR
This vulnerability allows unauthenticated remote attackers to bypass security policies on Cisco Firepower Threat Defense devices by exploiting a logic error in TCP Intercept handling with Snort 3. Only devices configured with Snort 3 detection engine are affected, while Snort 2 configurations remain safe. Attackers can send crafted traffic patterns to allow unintended traffic through the firewall.
💻 Affected Systems
- Cisco Firepower Threat Defense (FTD) Software
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Complete policy bypass allowing attackers to send any traffic through the firewall, potentially enabling lateral movement, data exfiltration, or malware delivery.
Likely Case
Selective policy bypass for specific traffic patterns, allowing some unauthorized communications while other security controls remain effective.
If Mitigated
Limited impact due to defense-in-depth controls, with other security layers detecting or blocking the bypassed traffic.
🎯 Exploit Status
Requires crafting specific TCP traffic patterns targeting embryonic connections. No public exploit code available at advisory publication.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 7.4.1 and later
Vendor Advisory: https://sec.cloudapps.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-snort-bypass-PTry37fX
Restart Required: Yes
Instructions:
1. Download FTD software version 7.4.1 or later from Cisco Software Center. 2. Upload to FTD device. 3. Install update via CLI or FMC. 4. Reboot device after installation completes.
🔧 Temporary Workarounds
Switch to Snort 2 detection engine
allTemporarily revert to Snort 2 detection engine which is not affected by this vulnerability
configure through FMC: Devices > Device Management > select device > Policies > Access Control > Advanced > Detection Engine > Set to Snort 2
🧯 If You Can't Patch
- Implement network segmentation to limit potential lateral movement if bypass occurs
- Deploy additional network monitoring and intrusion detection systems to detect policy bypass attempts
🔍 How to Verify
Check if Vulnerable:
Check FTD version via CLI: 'show version' and verify Snort 3 is configured in FMC under Access Control policiesCheck Version:
show version | include VersionVerify Fix Applied:
Verify version is 7.4.1 or later: 'show version' and confirm Snort 3 configuration remains active📡 Detection & Monitoring
Log Indicators:
- Unusual TCP connection patterns, policy bypass alerts, Snort 3 engine errors
Network Indicators:
- Abnormal TCP SYN flood patterns, unexpected traffic bypassing firewall rules
SIEM Query:
source="ftd" AND (event_type="policy_bypass" OR message="*TCP Intercept*" OR severity>=4)