The Noise Inside the Network: How an Unsophisticated Attack Exposed a Third-Party Risk

When unusual activity was detected on a European bank’s central IT system, its internal security team quickly recognized that the incident warranted immediate response. They discovered unauthorized VPN-based access attempts that spanned several months. They then engaged Unit 42 to determine the full scope of the intrusion, identify any persistent footholds and secure the environment.

While the activity appeared to be a stealthy cyberespionage campaign, the actual intrusion was made possible by gaps in foundational security controls. Rather than relying on novel techniques, the threat actor succeeded through persistence, exploiting weaknesses that stronger identity protections and basic security hygiene could have prevented. The case highlights an important lesson: Sometimes the most damaging intrusions begin with the simplest oversights.

Internal Reconnaissance: A High-Volume, Noisy Campaign

The intrusion originated through a third-party-managed external gateway appliance that was not properly configured to enforce strict authentication. Using compromised credentials, the attacker began by authenticating to internal systems. Once inside, the threat actor launched a discovery campaign of the internal network.

The threat actor conducted multiple rounds of reconnaissance, performing extensive host and network scans across a wide range of protocols and interacting with thousands of systems. This broad, noisy approach was less a targeted strike than casting a net to uncover as many access points as possible.

Authentication Abuse and Documentation Browsing

The pattern continued with credential testing. Over a period of a few months, the threat actor launched multiple password-guessing campaigns. They hammered at internal systems with brute-force authentication attempts, focusing on administrator accounts.

While doing this, they systematically targeted internal documentation and data shares. Using automated web requests, they scraped individual pages and attachments from internal systems and enumerated various operational and network shares.

The activity observed did not match the behavior typically associated with a sophisticated threat actor. The noise behind the scanning and login attempts, along with using common system identifiers, pointed to an opportunistic attacker attempting to compromise multiple systems. Their actions showed little effort to remain hidden or avoid detection.

Early Detection, Containment, and Remediation

In the final stages, the intruder attempted to expand control by exploiting a Windows Server Update Services (WSUS) remote code execution vulnerability on the central configuration management server. This server handled software distribution across the bank, making it a prime target for privilege escalation and long-term persistence.

However, the attacker’s luck ran out. The moment they attempted to execute unauthorized code, Cortex XDR identified the activity and contained the threat before it could escalate. The attacker was prevented from gaining a persistent foothold or moving laterally throughout the network.

When Unit 42 engaged, our team initiated a comprehensive threat-hunting effort. We performed a deep forensic review of endpoint telemetry across approximately thousands of systems, alongside logs from dozens of Windows and Linux servers. Ultimately, no additional attacker presence or persistent backdoors were found. Bank leadership acted quickly to review the exposed documentation and rotate all compromised credentials, completely neutralizing the threat.

What This Investigation Revealed

This case serves as a critical reminder that not every cyber threat is advanced and multifaceted. Opportunistic actors will gladly take advantage of simple oversight, such as missing multi-factor authentication (MFA) on a VPN or an unpatched edge device, to compromise and break into an environment. That being said, an attacker’s lack of sophistication doesn’t make them harmless.

Defending against this type of intrusion relies on foundational security hygiene and swift response. This includes:

• Enforcing strict identity access controls
• Ensuring timely patching
• Using endpoint detection to stop lateral movement

By pairing timely containment with thorough threat hunting, the organization prevented the intrusion from turning into a catastrophic event.

Outcomes

Unit 42 independently validated the incident to confirm the root cause, restoring leadership confidence through strategic guidance and complete incident management. Beyond resolving the immediate threat, we delivered specific, prioritized recommendations to harden the bank’s security posture. To ensure enhanced protection, the organization expanded its defensive coverage by deploying additional Cortex XSIAM and Cortex XDR licenses and broadening its incident response retainer service.

Interested in learning more about the latest attack trends? If so, take a look at our Unit 42 Global Incident Response Report, which distills the most critical findings based on our direct experience responding to over 750 real-world cyberattacks across the globe.

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