CVE-2023-0881
📋 TL;DR
This vulnerability allows attackers to cause a kernel crash (denial of service) by launching DDoS attacks against TCP port 22 (SSH) on affected systems. It affects systems running the linux-bluefield package with a specific backported commit missing subsequent fixes. The vulnerability is introduced through improper input validation in the nft_lookup functionality.
💻 Affected Systems
- linux-bluefield kernel package
📦 What is this software?
Linux Bluefield by Canonical
⚠️ Risk & Real-World Impact
Worst Case
Complete system crash requiring physical or remote console access to reboot, leading to extended service downtime and potential data corruption.
Likely Case
Service disruption affecting SSH availability and potentially other services due to kernel panic, requiring system reboot to restore functionality.
If Mitigated
Minimal impact with proper network filtering and rate limiting preventing the DDoS traffic from reaching vulnerable systems.
🎯 Exploit Status
Exploitation requires only network access to port 22 and ability to generate DDoS traffic, making it relatively simple to execute.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: Updated linux-bluefield package with the missing commits
Vendor Advisory: https://bugs.launchpad.net/ubuntu/+source/linux-bluefield/+bug/2006397
Restart Required: Yes
Instructions:
1. Update the linux-bluefield package via apt-get update && apt-get upgrade. 2. Reboot the system to load the patched kernel.
🔧 Temporary Workarounds
Network Filtering
LinuxBlock or rate limit traffic to TCP port 22 from untrusted sources
iptables -A INPUT -p tcp --dport 22 -m state --state NEW -m recent --set
iptables -A INPUT -p tcp --dport 22 -m state --state NEW -m recent --update --seconds 60 --hitcount 10 -j DROP
SSH Port Change
allChange SSH to a non-standard port to reduce exposure to automated attacks
Edit /etc/ssh/sshd_config: Port 2222 (or other)
systemctl restart sshd
🧯 If You Can't Patch
- Implement strict network access controls to limit SSH traffic to trusted sources only
- Deploy DDoS protection solutions to filter malicious traffic before it reaches vulnerable systems
🔍 How to Verify
Check if Vulnerable:
Check if running linux-bluefield kernel and compare version against patched versions in Ubuntu bug reportCheck Version:
uname -rVerify Fix Applied:
Verify kernel version after update matches patched version and system remains stable under port 22 traffic📡 Detection & Monitoring
Log Indicators:
- Kernel panic messages in /var/log/kern.log or dmesg
- High volume of SSH connection attempts in auth.log
Network Indicators:
- Unusual high-volume traffic to port 22 from single/multiple sources
- SSH service becoming unresponsive
SIEM Query:
source="kern.log" AND "kernel panic" OR source="auth.log" AND "sshd" AND event_count>1000 per_source per_hour