CVE-2023-27152
📋 TL;DR
CVE-2023-27152 is an authentication bypass vulnerability in DECISO OPNsense firewall software that allows attackers to perform unlimited brute-force login attempts. This affects OPNsense 23.1 installations, potentially allowing unauthorized access to firewall administration interfaces. Organizations using vulnerable OPNsense versions are at risk.
💻 Affected Systems
- DECISO OPNsense
📦 What is this software?
Opnsense by Opnsense
⚠️ Risk & Real-World Impact
Worst Case
Complete compromise of firewall administration leading to network takeover, credential theft, and lateral movement into protected networks.
Likely Case
Unauthorized administrative access to firewall allowing rule modification, traffic interception, and network disruption.
If Mitigated
Limited impact with proper network segmentation and monitoring, but still presents authentication bypass risk.
🎯 Exploit Status
Simple brute-force tools can exploit this vulnerability. No authentication required to attempt login.
🛠️ Fix & Mitigation
✅ Official Fix
Patch Version: OPNsense 23.1.1 and later
Vendor Advisory: https://forum.opnsense.org/index.php?topic=33415.0
Restart Required: No
Instructions:
1. Log into OPNsense web interface. 2. Navigate to System > Firmware > Updates. 3. Click 'Check for updates'. 4. Install available updates. 5. Reboot if prompted.
🔧 Temporary Workarounds
Implement IP-based rate limiting
allConfigure firewall rules to limit authentication attempts per IP address
Configure via OPNsense GUI: Firewall > Rules > WAN, add rule limiting connections to port 443/tcp
Enable fail2ban or similar protection
linuxInstall and configure fail2ban to block IPs after failed login attempts
pkg install py39-fail2ban
Configure /usr/local/etc/fail2ban/jail.local for OPNsense web interface
🧯 If You Can't Patch
- Implement network-level protection with WAF or reverse proxy that provides rate limiting
- Restrict administrative interface access to specific IP ranges only
🔍 How to Verify
Check if Vulnerable:
Check OPNsense version via web interface dashboard or CLI: opnsense-versionCheck Version:
opnsense-versionVerify Fix Applied:
Verify version is 23.1.1 or later: opnsense-version | grep -q '23.1.1' && echo 'Patched'📡 Detection & Monitoring
Log Indicators:
- Multiple failed login attempts from single IP in /var/log/system.log
- Rapid succession of authentication failures
Network Indicators:
- High volume of HTTPS requests to administrative port (default 443) from single source
- Unusual login patterns outside business hours
SIEM Query:
source="OPNsense" "login failure" | stats count by src_ip | where count > 10