Intrusion Detection Systems (IDS) in Cybersecurity - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is an Intrusion Detection System (IDS)?

An IDS is a security tool that monitors network or system activities for malicious actions or policy violations and alerts administrators when suspicious activity is detected.

beginner

Name the two main types of IDS based on deployment location.

The two main types are Network-based IDS (NIDS), which monitors network traffic, and Host-based IDS (HIDS), which monitors activities on individual devices.

intermediate

How does signature-based IDS detect threats?

Signature-based IDS detects threats by comparing network or system activity against a database of known attack patterns or signatures.

intermediate

What is the main difference between IDS and IPS?

IDS detects and alerts about suspicious activity but does not block it, while Intrusion Prevention Systems (IPS) can detect and actively block or prevent attacks.

intermediate

Why is false positive reduction important in IDS?

Reducing false positives is important because too many incorrect alerts can overwhelm security teams, causing real threats to be missed or ignored.

Which type of IDS monitors traffic on a network?

A Anomaly-based IDS

B Host-based IDS

C Signature-based IDS

D Network-based IDS

Network-based IDS (NIDS) monitors network traffic to detect suspicious activity.

What does a signature-based IDS rely on to detect attacks?

A Random sampling

B Known attack patterns

C User behavior analysis

D Encryption keys

Signature-based IDS uses a database of known attack patterns to identify threats.

Which of the following is NOT a function of an IDS?

A Blocking attacks automatically

B Alerting administrators about suspicious activity

C Monitoring system logs

D Detecting policy violations

IDS alerts but does not block attacks; blocking is done by IPS.

What is a common challenge when using IDS?

A Lack of network access

B Inability to monitor logs

C Too many false positives

D No alerts generated

False positives cause many incorrect alerts, making it hard to focus on real threats.

Host-based IDS primarily monitors:

A Individual device activities

B Internet traffic

C Firewall settings

D Email servers

Host-based IDS watches activities on a single device to detect suspicious behavior.

Explain the difference between Network-based IDS and Host-based IDS.

Think about where the IDS is placed and what it watches.

Describe how signature-based and anomaly-based IDS differ in detecting threats.

Consider how each method identifies suspicious activity.

Practice

1. What is the primary purpose of an Intrusion Detection System (IDS)?

easy

A. To monitor network or system activities for suspicious behavior

B. To automatically block all incoming network traffic

C. To replace firewalls in network security

D. To encrypt data during transmission

Solution

1. Step 1: Understand IDS function

   An IDS is designed to watch network or system activities to detect suspicious or malicious behavior.

2. Step 2: Differentiate from other tools

   Unlike firewalls or encryption tools, IDS does not block or encrypt but alerts about possible threats.

3. Final Answer:

   To monitor network or system activities for suspicious behavior -> Option A

4. Quick Check:

   IDS monitors and alerts [OK]

Hint: IDS alerts suspicious activity but does not block it [OK]

Common Mistakes:

• Confusing IDS with firewall that blocks traffic
• Thinking IDS encrypts data
• Assuming IDS replaces other security tools

2. Which of the following is the correct description of a Network-based IDS (NIDS)?

easy

A. Monitors network traffic for suspicious patterns

B. Monitors individual host activities only

C. Encrypts network data to prevent attacks

D. Automatically blocks detected intrusions

Solution

1. Step 1: Identify NIDS role

   NIDS monitors network traffic to detect suspicious patterns or attacks across the network.

2. Step 2: Exclude incorrect options

   It does not monitor individual hosts only, encrypt data, or block intrusions automatically.

3. Final Answer:

   Monitors network traffic for suspicious patterns -> Option A

4. Quick Check:

   NIDS watches network traffic [OK]

Hint: NIDS watches network traffic, not just one computer [OK]

Common Mistakes:

• Mixing NIDS with Host-based IDS
• Thinking NIDS blocks attacks automatically
• Confusing monitoring with encryption

3. Consider this simplified Python-like pseudocode for an IDS alert system:

alerts = []
for packet in network_traffic:
    if packet.source_ip == '192.168.1.100' and packet.port == 22:
        alerts.append('Possible SSH attack')
print(alerts)

What will be the output if two packets match the condition?

medium

A. Error: packet is undefined

B. ['Possible SSH attack']

C. []

D. ['Possible SSH attack', 'Possible SSH attack']

Solution

1. Step 1: Analyze the loop and condition

   The code checks each packet; if source IP is '192.168.1.100' and port is 22, it adds a message to alerts.

2. Step 2: Consider two matching packets

   Since two packets meet the condition, the message is appended twice, resulting in two identical alerts.

3. Final Answer:

   ['Possible SSH attack', 'Possible SSH attack'] -> Option D

4. Quick Check:

   Two matches add two alerts [OK]

Hint: Each matching packet adds one alert to the list [OK]

Common Mistakes:

• Assuming only one alert regardless of matches
• Thinking the list remains empty
• Confusing variable scope causing error

4. A system administrator wrote this IDS rule snippet:

if packet.protocol = 'TCP':
    alert('TCP packet detected')

What is the error in this code?

medium

A. No error, code is correct

B. Using single equals sign (=) instead of double equals (==) for comparison

C. Incorrect protocol name 'TCP'

D. Missing parentheses in alert function

Solution

1. Step 1: Identify the comparison operator

   The code uses '=' which is an assignment operator, not a comparison operator.

2. Step 2: Correct operator for condition

   For checking equality, '==' must be used to compare values in conditions.

3. Final Answer:

   Using single equals sign (=) instead of double equals (==) for comparison -> Option B

4. Quick Check:

   Use '==' to compare values in conditions [OK]

Hint: Use '==' for comparison, '=' is assignment [OK]

Common Mistakes:

• Confusing assignment and comparison operators
• Ignoring syntax errors from wrong operator
• Assuming protocol name is wrong

5. You want to design an IDS that detects suspicious login attempts by checking if a user fails to login 3 times in a row within 5 minutes. Which approach best applies IDS concepts to solve this?

hard

A. Use a Network-based IDS to block all login attempts after 3 failures

B. Use encryption to hide login attempts from attackers

C. Use a Host-based IDS to monitor login logs and trigger alerts on 3 failed attempts within 5 minutes

D. Use a firewall to allow only 3 login attempts per user

Solution

1. Step 1: Identify IDS type for login monitoring

   Host-based IDS monitors activities on a single computer, such as login logs, suitable for detecting failed login attempts.

2. Step 2: Understand IDS role and limits

   IDS alerts on suspicious activity but does not block actions automatically; blocking is done by other tools.

3. Final Answer:

   Use a Host-based IDS to monitor login logs and trigger alerts on 3 failed attempts within 5 minutes -> Option C

4. Quick Check:

   Host IDS monitors logs and alerts [OK]

Hint: Host IDS watches logs and alerts, does not block [OK]

Common Mistakes:

• Confusing IDS with blocking tools like firewalls
• Thinking IDS encrypts or blocks automatically
• Using network IDS for host-specific login events