CVE-2021-1230
📋 TL;DR
This vulnerability in Cisco Nexus 9000 Series Fabric Switches in ACI mode allows unauthenticated remote attackers to crash the BGP routing process by sending crafted BGP updates, potentially causing device reloads and denial of service. It affects both IBGP and EBGP implementations. Only devices configured with explicit BGP peers are vulnerable.
💻 Affected Systems
- Cisco Nexus 9000 Series Fabric Switches
📦 What is this software?
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⚠️ Risk & Real-World Impact
Worst Case
Complete network outage due to device reloads, disrupting all traffic through affected switches
Likely Case
Temporary routing instability and packet loss until BGP process restarts or device recovers
If Mitigated
No impact if proper BGP peer filtering and network segmentation are implemented
🎯 Exploit Status
Exploitation requires sending specific BGP update messages over established TCP connections from trusted peers, making it moderately complex but feasible for skilled attackers
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Cisco NX-OS in ACI mode Release 14.2(1) and later
Vendor Advisory: https://tools.cisco.com/security/center/content/CiscoSecurityAdvisory/cisco-sa-n9kaci-bgp-De9dPKSK
Restart Required: Yes
Instructions:
1. Download the fixed software from Cisco Software Center. 2. Upgrade to Release 14.2(1) or later. 3. Reload the device to apply the update.
🔧 Temporary Workarounds
BGP Peer Filtering
allImplement strict BGP peer filtering using access control lists to limit which IP addresses can establish BGP sessions
router bgp <AS_NUMBER>
neighbor <IP_ADDRESS> remote-as <AS_NUMBER>
neighbor <IP_ADDRESS> password <PASSWORD>
neighbor <IP_ADDRESS> prefix-list FILTER-IN in
TCP MD5 Authentication
allEnable TCP MD5 authentication for all BGP sessions to prevent unauthorized connections
router bgp <AS_NUMBER>
neighbor <IP_ADDRESS> password <MD5_KEY>
🧯 If You Can't Patch
- Implement strict network segmentation to isolate BGP traffic and limit exposure
- Deploy intrusion prevention systems to detect and block malicious BGP update patterns
🔍 How to Verify
Check if Vulnerable:
Check current software version with 'show version' and verify if running ACI mode software prior to 14.2(1)Check Version:
show version | include nxos.aciVerify Fix Applied:
After upgrade, verify version is 14.2(1) or later with 'show version' and test BGP stability📡 Detection & Monitoring
Log Indicators:
- BGP process crash logs
- Device reload events
- Unexpected BGP neighbor state changes
Network Indicators:
- Unusual BGP update patterns
- Rapid BGP session flaps
- Increased TCP resets on BGP port 179
SIEM Query:
source="cisco_nexus" AND ("BGP.*crash" OR "reload" OR "%BGP-5-ADJCHANGE")