The Categories Of Incidents According To US-CERT: Understanding And Responding Effectively

Cybersecurity relies on clear threat identification. The US-CERT (United States Computer Emergency Readiness Team) classifies incidents into 7 categories for better management and response to cyberattacks.

🛑 CAT0 – Testing and Evaluations

Authorized activities such as security audits and penetration tests to identify vulnerabilities.

🛑 CAT1 – Unauthorized Access

An unauthorized user gains access to a system, application, or confidential data.

🛑 CAT2 – Denial of Service (DoS/DDoS)

Attempts to make a service unavailable by overwhelming it with requests.

🛑 CAT3 – Malicious Code Attacks

Spread of viruses, ransomware, trojans, or other malware compromising security.

🛑 CAT4 – Misuse

Abuse or non-compliant use of IT resources by an internal user.

🛑 CAT5 – Scans and Probes

Detection of suspicious activities like network reconnaissance, port scanning, or vulnerability searches.

🛑 CAT6 – Investigations

In-depth analysis of incidents or abnormal behavior to detect potential latent threats.

Classifying incidents is crucial as it enables faster and more effective responses to cyberattacks.

You Should Know:

1. Testing and Evaluations (CAT0)

Nmap Scan (Network Reconnaissance):
```
nmap -sV -O target_ip
```
Nikto Vulnerability Scan:
```
nikto -h target_url
```

2. Unauthorized Access (CAT1)

Check Active Logins (Linux):
```
who
last
```

Detect SSH Intrusions:

grep "Failed password" /var/log/auth.log

3. Denial of Service (CAT2)

Monitor Network Traffic:
```
tcpdump -i eth0 -n
```

Block Suspicious IPs:

iptables -A INPUT -s attacker_ip -j DROP

4. Malicious Code Attacks (CAT3)

Scan for Malware with ClamAV:
```
sudo clamscan -r /home
```
Check Running Processes:
```
ps aux | grep -i "suspicious_process"
```

5. Misuse (CAT4)

Audit User Commands (Linux):
```
history
```
Check Sudo Logs:
```
cat /var/log/auth.log | grep sudo
```

6. Scans and Probes (CAT5)

Detect Port Scans with Fail2Ban:
```
sudo fail2ban-client status sshd
```
Analyze Firewall Logs:
```
journalctl -u firewalld --no-pager
```

7. Investigations (CAT6)

Memory Forensics with Volatility:

volatility -f memory_dump.raw imageinfo

Analyze Logs with Logwatch:
```
logwatch --detail High
```

What Undercode Say:

Understanding US-CERT’s incident classification helps organizations prioritize threats and respond effectively. Implementing proactive monitoring, logging, and defensive commands (like iptables, fail2ban, and clamav) strengthens cybersecurity posture. Regular audits (nmap, nikto) and forensic tools (volatility) ensure readiness against evolving threats.

Expected Output:

A structured incident response plan based on US-CERT categories.
Logs showing detected intrusion attempts (/var/log/auth.log).
Blocked IPs in firewall logs (iptables -L).
Malware scan reports (clamscan).
Network traffic analysis (tcpdump).

References:

Reported By: Yassirmaghzaz Cybersaezcuritaez – Hackers Feeds
Extra Hub: Undercode MoN
Basic Verification: Pass ✅

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