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A sharp observation from our colleagues at Truesec suggests that the attackers may have done more than just obtain working VPN credentials—they could have compromised the entire firewall, presumably using a zero-day exploit.
“Based on tests conducted of victims’ externally facing firewalls, the default behavior should assign an authenticated SSL-VPN user an IP from a predefined IP-address pool 10.10.11[.0]/24, and any traffic from an SSL-VPN connected client towards the internal LAN would be sourced from that assigned IP-address. Despite this expected behavior, traffic was sourced from 192.168.1[.]1 when the TA authenticated to any of the internal machines in the victims’ environment.”
Read more about Helldown Ransomware
You Should Know:
Detecting Firewall Compromise
1. Check VPN Logs for Anomalies:
grep "192.168.1.1" /var/log/fortinet/vpn.log
This helps identify if traffic is being routed from an unexpected internal IP.
2. Monitor Firewall Rules for Unauthorized Changes:
sudo iptables -L -n -v
Look for unexpected rules allowing inbound/outbound traffic.
3. Inspect Active VPN Sessions:
netstat -tulnp | grep ssl-vpn
Verify active connections and their source IPs.
4. Check for Zero-Day Exploits:
journalctl -u firewalld --since "1 hour ago" | grep -i "error|fail"
Review system logs for unusual errors.
Mitigation Steps
- Isolate the Firewall:
sudo ifconfig eth0 down
Disconnect from the network to prevent lateral movement.
- Apply Latest Patches:
sudo apt update && sudo apt upgrade -y
Ensure all security updates are applied.
- Reset VPN Credentials:
sudo cp /etc/ipsec.secrets /etc/ipsec.secrets.bak && sudo nano /etc/ipsec.secrets
Change all VPN credentials immediately.
- Block Suspicious IPs:
sudo iptables -A INPUT -s 192.168.1.1 -j DROP
Forensic Analysis
- Capture Network Traffic:
sudo tcpdump -i eth0 -w firewall_compromise.pcap
- Check for Backdoors:
find / -name ".sh" -type f -exec grep -l "192.168.1.1" {} \;
What Undercode Say:
Helldown Ransomware demonstrates the critical risks of VPN and firewall breaches. Attackers exploiting zero-day vulnerabilities can bypass standard security measures, making proactive defense essential. Regularly audit firewall rules, enforce strict VPN access controls, and monitor logs for anomalies. Immediate isolation, credential rotation, and traffic analysis are key to mitigating such threats.
Expected Output:
- Firewall logs indicating unauthorized IP sourcing (
192.168.1.1). - Unusual VPN session behavior.
- Detection of malicious traffic via packet capture.
- Successful blocking of attacker IPs via
iptables.
References:
Reported By: Stephan Berger – Hackers Feeds
Extra Hub: Undercode MoN
Basic Verification: Pass ✅
