How I Bypassed a Corporate Firewall
Published June 2025
During a recent internal network engagement, the client's firewall was configured with restrictive outbound rules, but as always — where there’s an egress, there’s a way.
Initial Setup
After landing a shell on an internal system via a phishing payload, I quickly realized most outbound ports were blocked — even 443. DNS was still open, though.
DNS Tunneling
I deployed a dnscat2 server on my VPS and connected via a PowerShell payload. While throughput was limited, I had enough bandwidth to exfil credentials and later upload a stager.
Payloads Used
- Initial loader via macro + mshta
- Stage 1 DNS reverse shell (dnscat2)
- Stage 2 PowerShell Empire stager
Lessons Learned
Organizations often overlook outbound traffic restrictions — especially DNS. I recommended egress filtering, application whitelisting, and DNS logging via SIEM as remediation.
This was a great example of why layered security matters. Firewalls aren’t magic — they’re just part of the story.