CVE-2021-27450
📋 TL;DR
This vulnerability involves weak SSH server configuration in the MU320E device that doesn't follow security best practices, potentially weakening SSH protocol strength. Attackers could leverage this as part of larger attacks to gain unauthorized access or escalate privileges. All organizations using MU320E devices with firmware versions prior to v04A00.1 are affected.
💻 Affected Systems
- MU320E
📦 What is this software?
⚠️ Risk & Real-World Impact
Worst Case
Full system compromise leading to unauthorized access, data exfiltration, or device takeover as part of a larger attack chain.
Likely Case
Weakened SSH security making brute force attacks easier, potentially leading to unauthorized access if combined with other vulnerabilities.
If Mitigated
Minimal impact with proper network segmentation, strong authentication, and monitoring in place.
🎯 Exploit Status
Requires attacker to have network access and knowledge of SSH weaknesses; often exploited as part of multi-stage attacks
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: v04A00.1
Vendor Advisory: https://us-cert.cisa.gov/ics/advisories/icsa-21-082-02
Restart Required: Yes
Instructions:
1. Download firmware v04A00.1 from vendor portal
2. Backup current configuration
3. Apply firmware update via management interface
4. Reboot device
5. Verify SSH configuration hardening
🔧 Temporary Workarounds
SSH Configuration Hardening
linuxManually implement SSH security best practices to mitigate weak configuration
# Edit /etc/ssh/sshd_config
Protocol 2
PermitRootLogin no
MaxAuthTries 3
ClientAliveInterval 300
ClientAliveCountMax 2
UsePAM yes
AllowUsers specific_user
# Restart SSH service
🧯 If You Can't Patch
- Implement network segmentation to isolate MU320E devices from untrusted networks
- Deploy SSH bastion hosts with strict access controls and monitoring
🔍 How to Verify
Check if Vulnerable:
Check firmware version via web interface or CLI: show versionCheck Version:
show versionVerify Fix Applied:
Verify firmware version is v04A00.1 or later and review SSH configuration for best practices📡 Detection & Monitoring
Log Indicators:
- Failed SSH authentication attempts
- Unusual SSH connection patterns
- Configuration changes to SSH service
Network Indicators:
- SSH brute force attempts
- Unusual SSH traffic to MU320E devices
- SSH connections using weak ciphers
SIEM Query:
source="ssh_logs" AND (event="Failed password" OR event="Invalid user") AND dest_ip="MU320E_IP"