Monitoring The Network Perimeter

 Monitoring the Network Perimeter

Monitoring the perimeter involves using:

  • Firewalls

  • Intrusion Detection/Prevention Systems (IDS/IPS)

  • Access Control


Purpose:
  • Spot early-stage attacks (e.g., port scans, brute-force attacks)

  • Detect misconfigurations exposing sensitive services

  • Identify outbound traffic anomalies that may indicate malware or data exfiltration



Scenario 1(Port Scanning):


Shown above is a classic port scanning where same external IP attempt to connect to the same intetrnal IP within shor period of time. The attacker actively searching for open services to target. 


Scenario 2 (Web server attack) 

based on  WAF log above:

  • Logs contain both ALLOW and BLOCK actions.

  • Filtering for action=BLOCK quickly reveals threats.

  • WAF identifies attack type and blocks malicious requests.


So the verdict is Multiple web attacks detected and blocked, meaning that there is high-confidence indication that the website is being actively targeted.

Scenario 3 (VPN Brute force attack)


Indicators

  • Large number of FAILED_AUTH events.

  • Repeated login attempts against the VPN gateway.

  • Common usernames targeted (e.g., admin, guest, user).

Log Characteristics

  • Mix of:

    • FAILED_AUTH

    • SUCCESS_AUTH

  • Legitimate users generate occasional successful logins.

  • Attackers generate a high volume of failed logins.

Investigation Method

  • Filter or group logs by source IP.

  • Look for IPs generating hundreds of failed login attempts in a short period.

Analyst Verdict

  • Brute-force attack against the VPN gateway.

  • Attacker is attempting to discover valid credentials.


Suspicious Patterns to Look For

Pattern

Possible Threat

One source → Many destinations

Scanning

One source → One destination repeatedly

Brute-forcing

Traffic at perfect, regular intervals

Malware beaconing


Key Takeaways

  • The analyst's role is to distinguish normal traffic from suspicious activity.

  • Look for repetitive and unusual patterns.

  • IDS/WAF alerts provide valuable context about why activity was flagged.

  • Monitoring the network perimeter is the first step in detecting attacks.

  • Context helps determine whether activity is malicious or benign.




















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