The Loose Link: A Phishing Email That Almost Destroyed a Business

The Loose Link: A Phishing Email That Almost Destroyed a Business

It started, as many breaches do, with a single click.

I was consulting for a small marketing agency, 20 employees, a decent client base, and no dedicated IT team. They’d reached out after one of their employees received a strange email.

The subject line read: “Invoice Inquiry: URGENT”.

That was the loose link.

The First Mistake: The Click That Opened the Door

The employee, a junior account manager, thought the email was from a client. The sender’s address looked familiar, just one letter off. The body of the message was professional enough, asking her to review an invoice.

She clicked.

At first, nothing happened. The PDF looked blank. She moved on with her day, completely unaware that she had just become the first step in a cyber kill chain.

The Cyber Kill Chain: How the Attack Unfolded

1️⃣ Reconnaissance

The attackers had done their homework. The phishing email wasn’t random. It referenced a real client by name, using details likely scraped from LinkedIn or scraped company data.

They targeted the weakest link, an employee with access to client files but without much technical training.

2️⃣ Weaponization & Delivery

The attachment was a weaponized PDF containing an embedded macro exploit, a classic T1193 phishing tactic. Once opened, it executed a small but powerful PowerShell payload (T1059.001) that reached out to a command-and-control (C2) server, hidden behind a compromised web server in Eastern Europe.

3️⃣ Exploitation

The exploit used a known vulnerability (CVE-2017-11882), an old Microsoft Office bug still unpatched on the victim’s system. The attackers gained an initial foothold, setting up a remote access tool (RAT, T1219) to maintain persistence.

4️⃣ Installation & Persistence

Within hours, the attackers had moved laterally across the network. They scanned for open shares (T1135), found weak admin credentials stored in plain text, and installed Cobalt Strike beacons on key systems.

The attacker created scheduled tasks (T1053.005) to ensure they’d survive reboots.

5️⃣ Command & Control (C2)

Data exfiltration began quietly. Sensitive client files, passwords, and financial records were zipped and uploaded to an external server via encrypted HTTPS traffic that blended in with normal web activity (T1071.001).

6️⃣ Actions on Objectives: The Ransomware Drops

On Day 3, the real payload arrived: Black Basta ransomware, one of the newer ransomware-as-a-service strains. The attackers encrypted key files, locked databases, and left a ransom note demanding $100,000 in Bitcoin. They also threatened to leak sensitive client files unless the ransom was paid.

The Aftermath: What We Found (and What We Learned)

Through forensic analysis, we discovered:

  • The phishing email’s domain had been registered 48 hours before the attack, an early indicator they were setting up infrastructure.
  • Their PowerShell payload used base64 encoding to avoid detection (T1027.001).
  • The attackers used living off the land techniques (LOLBins) like certutil and bitsadmin to stay under the radar.
  • The lack of MFA and outdated systems gave them easy access.

The attack was stopped, barely. The agency refused to pay, and we were able to recover from backups, but they still suffered days of downtime and lost client trust.

This story isn’t unique. It’s happening to small businesses everywhere, every day.

The lesson? Phishing isn’t just an inbox nuisance. It’s the first domino in a kill chain that can lead to data loss, ransomware, and business collapse.

Training, patching, strong passwords, and multi-factor authentication aren’t “nice-to-haves.” They’re the foundation of survival in today’s cyber landscape.

So, ask yourself:
Who’s the loose link in your business?
And what can you do, today, to strengthen that link before the next phishing email lands in your inbox?

Let’s stay vigilant. Let’s stay informed. And as always, let’s discuss security.