Alerting to Data Exfiltration via Firewall Logs

For cybersecurity, data leaks, insider threats, and learning the firewall logs are critical for your business. Today I wanted to explain how you can guiltlessly watch your firewall logs for data theft or insider threats. It sounds like a lot, but when you break it down it’s easier than you think.

What is Data Exfiltration?

In layman’s terms, the data exfiltration process is an unauthorized transfer of data from your organism to an outside location. Imagine a person stealthily smuggling company secrets or sensitive customer data out the door without proper authorization. It may occur via hackers, malware or even trusted employees who go rogue.

Why should you care?

• It results in huge economical loss
• Harms your business’ image
• Brings legal trouble

Data exfiltration is one of the sneakier attacks since it often flies under the radar. That’s where logging and monitoring come into play.

Patterns of Unusual Outbound Traffic

Perhaps the first thing you want to search for in your firewall logs are abnormal outbound network traffic. With internal data leaks, stolen data typically exits your network via outbound traffic. Here’s how to detect unusual activity:

• Sudden spikes in data transfer: Does data inexplicably spike at odd hours?
• Connections with unknown IPs: Your firewall logs will have connections from IPs trying to connect other than yours. Do they come from trusted partners, or bad actors?
• Small transfers, one after another: Sometimes there isn’t one big file, and thieves break files down into smaller parts so as not to be detected.

Opt for low-traffic periods in your network — like late at night or holidays. If you are mobile then, you have big red flags on you. Important to note, not all spikes are bad. But in combination with other clues, they can indicate trouble.

Spotting Suspicious Transfers

Having detected abnormal activity, you wish to dig down into what exactly is flowing out. Monitoring firewall logs can enable you to:

• Keep an Eye on file sizes: Large unexpected file transfers could raise the flag.
• Inspect protocols and ports: Transferring files over unusual ports can be an effort to gain a way around security.
• Look for repeated failures and successes: Insider threats occasionally will try multiple times before they actually succeed.

It is also wise to cross-reference user activity logs against firewall data. For example:

• A user who had access to sensitive files, then suddenly started generating outbound traffic
• More than one session from the same user but elsewhere

As you won’t get the entire contents of the files using the firewall, but with the combination of logs with your internal systems, you can draw the painting of the full picture.

Pursuing Forensics With Firewall Logs

When you have reason to believe a breach or data theft has occurred, firewall logs are like your detective’s notebook. Here’s how to use them for forensics:

• Analyze suspicious traffic to correlate with specific timings and events.
• IP and geolocation analysis: Understand where the attack originated and where it was directed.
• Connection length & frequency: Long-lived or freq connections could be indicative of ongoing exfil.
• Use of encryption: Attackers will encrypt data and send it over an encrypted stream to avoid detection.

Collecting all this information together helps build up a picture of the incident. It also tells you what to block or monitor next. The trick is to keep firewall logs long enough to do this, so don’t set your log retention too low.

Preventing Insider Threats

Insider threats are not only about finding the bad actors — they are about preventing them before any damage occurs. Here are a few things you can do:

• Implement restrictive access: Only allow users to access what they require to do their jobs.
• Behavior analytics: Monitor automatically to catch unusual patterns.
• Develop your team: Raise awareness among employees regarding the dangers and symptoms of insider threats.
• Segment your networks: Restrict lateral movement within your systems.
• Regular audits: Do regular re-visits on user account permissions, review logs, identify user activity.

Keep in mind that insider threats are not always malicious. In some instances, they occur unintentionally or from mishap. So you have to do both in your approach.

Finally, the best solution to use as is a monitoring for the data exfiltration through the firewall logs is effective and has become a must for the most organizations in this digital world. By monitoring strange outbound traffic, detecting suspicious transfers, using firewall logs for detailed forensics, and working to prevent insider threats, a significant portion of data leaks can be mitigated.

Be wary, prioritize logging, and always seek out those red flags before it’s too late. Your company’s security is at stake.

The best everyday protection, however, attempts to keep data leaks, firewall logs and insider threats at the forefront of your cybersecurity strategy.