CVE-2021-38598
📋 TL;DR
This vulnerability in OpenStack Neutron allows attackers controlling a server instance to impersonate hardware addresses (MAC addresses) of other systems on the network when using the linuxbridge driver with ebtables-nft on Netfilter platforms. This can lead to denial of service or traffic interception. Affected are OpenStack deployments using vulnerable Neutron versions with specific configurations.
💻 Affected Systems
- OpenStack Neutron
📦 What is this software?
Neutron by Openstack
Neutron by Openstack
Neutron by Openstack
⚠️ Risk & Real-World Impact
Worst Case
Complete network disruption through ARP poisoning, man-in-the-middle attacks intercepting sensitive traffic between virtual machines, and persistent denial of service across the cloud environment.
Likely Case
Targeted denial of service against specific virtual machines or services, potential interception of unencrypted traffic between instances on the same network segment.
If Mitigated
Limited impact if network segmentation is properly implemented, traffic is encrypted, and monitoring detects ARP anomalies.
🎯 Exploit Status
Exploitation requires control of a server instance (compromised VM) and knowledge of target MAC addresses. The attack uses standard ARP spoofing techniques adapted for the virtual environment.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: 16.4.1, 17.1.3, or later versions
Vendor Advisory: https://launchpad.net/bugs/1938670
Restart Required: Yes
Instructions:
1. Upgrade Neutron to patched version. 2. Restart neutron-linuxbridge-agent services on all compute nodes. 3. Verify ebtables rules are properly applied.
🔧 Temporary Workarounds
Switch to iptables-legacy
linuxTemporarily revert to iptables-legacy instead of ebtables-nft to avoid the vulnerable code path
update-alternatives --set iptables /usr/sbin/iptables-legacy
systemctl restart neutron-linuxbridge-agent
Network segmentation
allImplement strict network segmentation to limit the blast radius of potential attacks
🧯 If You Can't Patch
- Implement strict network access controls between virtual machine instances
- Enable monitoring for ARP anomalies and MAC address changes in the virtual network
🔍 How to Verify
Check if Vulnerable:
Check Neutron version with 'neutron --version' and verify if using linuxbridge driver with ebtables-nft. Review /etc/neutron/plugins/ml2/linuxbridge_agent.ini for driver configuration.Check Version:
neutron --version | grep -o '[0-9]\+\.[0-9]\+\.[0-9]\+'Verify Fix Applied:
After patching, verify version is 16.4.1+, 17.1.3+, or later. Test ARP spoofing attempts should fail. Check that ebtables rules are properly enforced.📡 Detection & Monitoring
Log Indicators:
- Unusual ARP traffic patterns in neutron logs
- Multiple MAC addresses claiming same IP
- Unexpected changes in bridge forwarding tables
Network Indicators:
- ARP packets with spoofed source MAC addresses
- Duplicate MAC addresses on network segments
- Unusual traffic redirection patterns
SIEM Query:
source="neutron-logs" AND ("ARP" OR "MAC" OR "spoof") AND ("unusual" OR "duplicate" OR "conflict")