Incident Summary

An organization experienced a potential data exfiltration attempt after abnormal outbound network traffic was detected from an internal file server. The activity involved a large volume of files being transferred to an unfamiliar external destination outside normal business hours.

The alert was immediately escalated to i6 Security Operations, where analysts began investigating the unusual activity. The investigation revealed that a compromised user account was being used to access sensitive files and transfer them outside the organization.

Thanks to rapid monitoring and response, i6 successfully detected and stopped the data exfiltration attempt before sensitive information could leave the network.

How the Incident Started

The incident began when attackers obtained valid user credentials through an earlier credential compromise. Using these credentials, the attacker logged into the corporate network and began accessing shared storage systems.

Once inside, the attacker started browsing internal directories and collecting documents containing operational and internal business data. The attacker then attempted to compress and transfer these files to an external server under their control.

Detection by i6 Security Monitoring

Several indicators triggered security alerts, allowing the security team to quickly identify suspicious behavior:

• Large outbound data transfers to an unknown external IP
• File access activity occurring late at night
• Unusual login behavior linked to the user account
• Repeated attempts to access multiple sensitive directories

These indicators raised suspicion and triggered an immediate investigation by the i6 SOC team, ensuring the activity was analyzed without delay.

Investigation by i6 Security Analysts

Once the alert was received, the i6 analysts began a structured investigation to determine the scope and intent of the activity. The investigation was divided into multiple stages to ensure complete visibility.

1. Log Analysis and Activity Correlation

The first step involved analyzing authentication logs, file access logs, and network traffic records. This helped identify the user account responsible, the timeline of events, and the systems accessed.

• Identified the compromised user account
• Determined when suspicious activity began
• Tracked internal systems accessed

The logs confirmed that the activity originated from a legitimate account but was being used abnormally and from an unfamiliar system.

2. File Access and Data Movement Analysis

The next stage focused on identifying the files accessed and the volume of data involved. Analysts reviewed file server logs and discovered access to sensitive operational documents.

The attacker attempted to bundle multiple files together and prepare them for transfer, clearly indicating a data exfiltration attempt.

3. External Connection and Threat Intelligence Verification

The final stage involved analyzing the external destination receiving the data. Network telemetry revealed the remote IP address involved.

Threat intelligence confirmed that the destination had previously been associated with suspicious infrastructure, validating that the activity was malicious.

Immediate Response by i6

After confirming the attempted exfiltration, immediate containment actions were taken to stop the attack and prevent further access.

• Blocking the external IP address involved in the transfer
• Disabling the compromised user account
• Terminating active sessions associated with the activity
• Isolating the affected server for further investigation

These actions effectively halted the attack in real time and prevented data loss.

Containment and Remediation

Following containment, the investigation continued to ensure no additional systems were impacted and the threat was fully removed.

• Reviewing privileged account activity across the network
• Conducting endpoint scans for malware or backdoors
• Resetting potentially exposed credentials
• Verifying no additional data transfers occurred

These measures ensured that the attacker could no longer access the environment and eliminated any lingering risks.

Security Improvements Implemented

After resolving the incident, i6 worked with the organization to strengthen its security posture and reduce the likelihood of similar incidents in the future.

• Enhanced monitoring for large outbound data transfers
• Additional alerts for abnormal file access patterns
• Improved identity and access management controls
• Strengthened network visibility and logging

These improvements significantly increased the organization's ability to detect and respond to advanced threats.

Conclusion

Data exfiltration attacks often rely on compromised credentials and subtle activity that may go unnoticed without proper monitoring.

In this case, i6’s proactive monitoring and structured investigation process quickly identified the suspicious behavior and stopped the attacker before sensitive information could be stolen.

The incident highlights the importance of continuous monitoring, strong access controls, and rapid incident response in protecting critical organizational data.