CVE-2022-20623
📋 TL;DR
This vulnerability allows unauthenticated remote attackers to cause BFD traffic to be dropped on affected Cisco Nexus 9000 Series switches by sending crafted traffic. This leads to BFD session flaps, route instability, and denial of service. Only Cisco Nexus 9000 Series switches running vulnerable NX-OS software versions are affected.
💻 Affected Systems
- Cisco Nexus 9000 Series Switches
📦 What is this software?
Nx Os by Cisco
Nx Os by Cisco
Nx Os by Cisco
⚠️ Risk & Real-World Impact
Worst Case
Complete network disruption with widespread BFD session failures causing route instability, traffic blackholing, and extended denial of service across the network fabric.
Likely Case
Intermittent BFD session flaps leading to route churn, increased latency, and periodic traffic drops affecting network stability.
If Mitigated
Minimal impact with proper rate limiting controls and network segmentation in place, potentially causing only localized BFD issues.
🎯 Exploit Status
Exploitation requires sending a crafted stream of traffic through the device, which is relatively straightforward for attackers with network access.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: NX-OS 9.3(9), 10.2(6), 10.3(4) or later
Vendor Advisory: https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-nxos-bfd-dos-wGQXrzxn
Restart Required: Yes
Instructions:
1. Download the appropriate fixed software version from Cisco Software Center. 2. Perform an in-service software upgrade (ISSU) if supported. 3. If ISSU not supported, schedule maintenance window and perform disruptive upgrade. 4. Verify upgrade completion and BFD functionality.
🔧 Temporary Workarounds
Disable BFD
cisco-nxosCompletely disable BFD functionality on affected devices to eliminate the vulnerability vector.
no feature bfd
Implement ACLs to restrict BFD traffic
cisco-nxosApply access control lists to limit which sources can send BFD traffic to the device.
ip access-list bfd-restrict
permit udp trusted-source any eq 3784
deny udp any any eq 3784
interface vlan X
ip access-group bfd-restrict in
🧯 If You Can't Patch
- Implement strict network segmentation to isolate BFD traffic to trusted sources only
- Deploy intrusion prevention systems (IPS) to detect and block BFD exploitation attempts
🔍 How to Verify
Check if Vulnerable:
Check NX-OS version with 'show version' and compare against vulnerable versions. Verify BFD configuration with 'show feature | include bfd' and 'show run | include bfd'.Check Version:
show version | include "NXOS: version"Verify Fix Applied:
After upgrade, verify version with 'show version' shows patched version. Monitor BFD sessions with 'show bfd neighbors' for stability.📡 Detection & Monitoring
Log Indicators:
- Increased BFD session flaps in logs
- Route instability events
- BFD state change messages
Network Indicators:
- Unusual BFD packet patterns
- High rate of BFD control packets from single sources
- Increased BFD session resets
SIEM Query:
source="nxos" AND ("BFD" AND ("flap" OR "reset" OR "down")) AND count by src_ip > threshold