CVE-2022-20751
📋 TL;DR
This vulnerability in Cisco Firepower Threat Defense (FTD) Software allows an unauthenticated remote attacker to cause a denial of service (DoS) by exploiting insufficient memory management in the Snort detection engine. Attackers can send crafted IP packets to trigger memory consumption, potentially disrupting all traffic or causing device reloads. It affects FTD devices running vulnerable software versions.
💻 Affected Systems
- Cisco Firepower Threat Defense (FTD) Software
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Device experiences out-of-memory condition, leading to complete traffic interruption or device reload, resulting in prolonged DoS.
Likely Case
Sustained attack causes memory exhaustion, degrading performance or causing temporary DoS until device recovers or is restarted.
If Mitigated
With patches applied, no impact; without patches, network segmentation and monitoring may limit exposure but not prevent exploitation.
🎯 Exploit Status
Exploitation requires sending a series of crafted IP packets to generate specific Snort events; no public proof-of-concept has been disclosed.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Fixed in versions 7.0.1, 7.1.0, and 7.2.0; earlier versions have specific patches (e.g., 6.6.5.2, 6.7.0.3).
Vendor Advisory: https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-ftd-snort-dos-hd2hFgM
Restart Required: Yes
Instructions:
1. Check current FTD version using 'show version' command. 2. Download and apply the appropriate patch from Cisco Software Center. 3. Reboot the device as required after patching. 4. Verify the fix by checking the version and monitoring for memory issues.
🔧 Temporary Workarounds
Disable Snort Detection Engine
allTemporarily disable the Snort engine to prevent exploitation, but this reduces threat detection capabilities.
configure terminal
no snort-engine
write memory
Implement Rate Limiting
allUse network controls to limit incoming packet rates to reduce the impact of crafted packets.
🧯 If You Can't Patch
- Isolate affected devices in a segmented network to limit blast radius and monitor for anomalous traffic.
- Enable strict logging and alerting for memory consumption spikes or Snort event anomalies to detect potential attacks early.
🔍 How to Verify
Check if Vulnerable:
Run 'show version' on the FTD device and compare the version against Cisco's advisory; versions prior to patched ones are vulnerable.Check Version:
show versionVerify Fix Applied:
After patching, run 'show version' to confirm the updated version and monitor system logs for absence of memory exhaustion alerts.📡 Detection & Monitoring
Log Indicators:
- High memory usage alerts in system logs
- Snort engine crash or restart events
- Out-of-memory errors in device logs
Network Indicators:
- Unusual spikes in IP packet traffic targeting the device
- Patterns of crafted packets matching Snort event triggers
SIEM Query:
source="ftd_logs" AND (message="memory exhaustion" OR message="snort crash")