Threat Hunting: An Advanced Guide to Log Analysis for Cybersecurity

In Part I of this series, we laid the groundwork for effective threat hunting by focusing on authentication logs. Techniques such as detecting suspicious system user logins, unauthorized access to systems, and identifying anomalies in login patterns helped establish a structured approach to uncovering potential threats. These foundational methods highlight how a proactive mindset can transform log data into actionable insights.

But threat hunting doesn’t stop at authentication logs. Attackers constantly evolve their tactics, and as defenders, we must expand our scope to analyze other critical log categories. Advanced threat hunting involves diving deeper into network traffic, endpoint behaviors, file changes, and application activity. By leveraging command-line tools like grep, awk, and cut, we can efficiently parse vast amounts of data to uncover hidden threats.

In this continuation, we’ll explore advanced techniques that build upon the basics from Part I. These strategies will enable you to go beyond surface-level anomalies and detect more sophisticated threats lurking in your systems. Let’s dive in!

Advanced Threat Hunting Techniques

1. Network Traffic Analysis

Network logs provide visibility into the communication patterns within your organization. Here’s how to leverage them for threat hunting:

Unusual Data Transfers

Large uploads or downloads to unfamiliar destinations often indicate data exfiltration or unauthorized activity. To identify such anomalies, you can use tools like grep, awk, or cut to parse network logs, which often include fields such as source/destination IPs, ports, and data size.

Examples

For Firewall Logs (iptables, ufw):

  
    grep "DPT" /var/log/syslog | awk '$NF > 5000 {print $1, $2, $3, $NF}'

DPT indicates the destination port. $NF (last field) may represent packet size or data transferred.

For Proxy Logs (e.g., Squid):

  
    grep "POST" /var/log/squid/access.log | awk '$5 > 5000 {print $1, $4, $5}'

$5 is the size of the uploaded data. $1 and $4 show the client IP and timestamp.

For Network Monitoring Tools (e.g., Zeek):

  
    awk '$9 > 5000 {print $1, $2, $3, $9}' conn.log

$9 refers to the total bytes transferred.

Outbound Connections to Unknown IPs

Flag connections to untrusted or foreign IPs by filtering logs for external traffic:

grep "OUTBOUND" /var/log/firewall.log | awk '{print $5}' | sort | uniq -c | sort -nr

Combine this with a threat intelligence feed to match flagged IPs against known malicious addresses.

Port Scanning Attempts

Repeated attempts on different ports from the same IP could indicate reconnaissance:

grep "connection attempt" /var/log/network.log | awk '{print $5}' | sort | uniq -c | sort -nr

2. File Integrity Monitoring

File integrity logs are vital for spotting unauthorized changes to critical files.

Detect Unexpected Modifications

Look for changes in system configuration files:

grep "modified" /var/log/fim.log | grep "/etc/" | cut -d " " -f1,3,5

This example filters logs for modifications in the /etc directory.

Identify Suspicious File Names

Flag unusual file names or extensions in monitored directories:

find /monitored/dir -type f -name "*.exe" -o -name "*.tmp"

3. Privileged Account Usage

Admin accounts are a key target for attackers. Monitoring their usage is crucial.

Track Privilege Escalation Attempts

Identify when a user gains elevated privileges unexpectedly:

grep "sudo:" /var/log/auth.log | awk '$NF == "success" {print $1, $2, $3, $11}'

Multiple Admin Logins

Detect concurrent logins from different locations:

grep "Accepted publickey" /var/log/auth.log | awk '{print $9, $11}' | sort | uniq -c

This identifies unique user-IP combinations.

4. Endpoint Behavior Analysis

Endpoint logs provide granular insights into device activities.

Identify Unusual Processes

Look for rare processes running on endpoints:

ps aux | awk '{print $1, $2, $11}' | sort | uniq -c | sort -n

Spot Persistence Mechanisms

Track newly created startup items:

grep "cron" /var/log/cron.log | grep "added"

5. Application and API Monitoring

Logs from web applications and APIs often reveal exploitation attempts.

Detect Abnormal API Calls

Spot spikes in API usage:

grep "API" /var/log/application.log | awk '{print $1, $3}' | sort | uniq -c | sort -nr

SQL Injection Attempts

Identify patterns indicative of injection attacks:

grep -E "SELECT|UNION|DROP|INSERT" /var/log/web.log | cut -d " " -f1,4,8

Repeated Failed Authentication

Flag brute-force attempts:

grep "failed login" /var/log/application.log | awk '{print $5}' | sort | uniq -c | sort -nr

6. Threat Hunting with Contextual Intelligence

Integrating external threat intelligence can elevate your threat-hunting capabilities.

Correlate Indicators of Compromise (IOCs)

Cross-reference IPs from logs with external feeds:

grep "IP" /var/log/firewall.log | cut -d " " -f5 | while read ip; do curl -s "https://threatfeed.com/api/$ip"; done

Flag Suspicious Domains

Use domain reputation services to flag high-risk domains accessed by users:

grep "domain" /var/log/dns.log | cut -d " " -f5 | while read domain; do curl -s "https://reputation.noc.org/api/?domain=$domain"; done

Advanced threat hunting requires a deep understanding of your environment and effective use of tools to parse and analyze logs. By applying techniques like network traffic analysis, file integrity monitoring, and contextual intelligence integration, you can uncover threats that traditional automated systems might overlook. Combine these strategies with the fundamentals covered in Part I to build a robust, proactive defense against cyber threats.

Happy hunting!