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Believe it or not: attackers can mask traffic to appear as legitimate data transfers, bypassing a firewall’s intrusion detection features

December 16, 2024

Believe it…flimsy financial firewalls permitted a huge breach of customers’ data. Firewalls don’t always prevent breaches. Layered security is important, and humans play a critical part

The Great Financial Breach of 2022

In 2022, a mid-sized financial services firm, “GreenCrest Capital”, faced a catastrophic data breach. Despite investing in a state-of-the-art firewall, they became the target of a sophisticated cyberattack that exposed the sensitive financial data of thousands of clients.

The Setup: A Misconfigured Firewall

GreenCrest Capital had deployed a next-generation firewall with advanced intrusion prevention systems. However, due to pressure to meet compliance deadlines, the IT team rushed the implementation with one critical oversight: they had left a default “allow all” rule in place for outbound traffic during testing which they forgot to remove when the firewall went live.

The Attack: A Trojan in Disguise

The attack began with a well-crafted phishing email sent to a GreenCrest employee. The email appeared to come from the company’s HR department, offering a bonus payout linked to a PDF document. The employee downloaded the PDF, which was a Trojan horse named StealthFox.

The Trojan installed a backdoor on the victim’s workstation, connecting to a command-and-control (C2) server. This connection should have been flagged or blocked by the firewall. However, because of the misconfigured outbound rule, the malware’s communication with the C2 server went undetected.

Exploitation: Lateral Movement

Using the backdoor, the attackers gained access to the company’s internal network. The firewall’s intrusion detection features could have stopped this activity, but the attackers cleverly masked their traffic to appear as legitimate data transfers. They also exploited a weakness in the firewall’s application-layer inspection, which failed to identify malicious SQL commands being sent to the company’s databases.

Once inside, the attackers used a combination of privilege escalation techniques to gain administrator rights and exfiltrated customer data through encrypted channels—a blind spot for the firewall due to insufficient SSL inspection.

The Fallout

By the time GreenCrest’s security team discovered the breach, the attackers had already stolen over 50GB of sensitive data, including account numbers, social security numbers, and financial transaction logs. The firm faced regulatory fines, lawsuits, and a severe blow to its reputation.

Lessons Learned

Misconfigurations kill: Even the most advanced firewalls are only as effective as their configuration. Regular audits could have caught the “allow all” rule.
Layered security is critical: Over-reliance on the firewall left GreenCrest vulnerable. Endpoint detection and response (EDR) tools might have stopped the malware at the workstation level.
Encryption inspection matters: Proper SSL inspection would have revealed malicious data exfiltration in encrypted channels.
Employee awareness: The phishing email succeeded because of a lack of cybersecurity training for employees.

This story is a testament that even the best technology can fail when humans overlook crucial details. It serves as a stark reminder to never treat firewalls—or any single security measure—as a panacea for cyber threats.