Man-in-the-Middle (On-Path) Attacks | AP Cybersecurity

AP Cybersecurity Topics › Man-in-the-Middle

Unit 3 • Topic 3.1 • Network Vulnerabilities and Attacks

Man-in-the-Middle (On-Path) Attacks Explained

A man-in-the-middle (on-path) attack places an adversary between two communicating parties so they can read or alter the traffic. On a local network, ARP spoofing is a common way to get there.

How an on-path attack works
Why encryption is the key defense
Real-world example
Key terms
Match it up
Check for Understanding
FAQ

On-pathattacker sits in the middle

Reads / altersintercepted traffic

TLSdefeats reading the data

An on-path attacker relays traffic between two parties, reading or altering it.

How an on-path attack works

In a man-in-the-middle attack, the adversary positions themselves so all traffic between two parties passes through them. They can silently read it, or alter it before passing it along. On a LAN, ARP spoofing is the usual method: the attacker tricks both sides into sending traffic to the attacker's MAC.

Public or unsecured networks make this easier, which connects back to the public Wi-Fi risks in Unit 1.

Scenario

On an open network, an attacker captures a victim's unencrypted login as it passes through. What attack is this?

Reveal answer

A man-in-the-middle (on-path) attack. The attacker sits between the victim and the server and reads the unencrypted traffic in transit.

Exam tip

On-path attacks intercept traffic in transit. The defense that matters most is encryption (TLS): even if intercepted, the data is unreadable.

Why encryption is the key defense

Encryption does not stop an attacker from sitting on-path, but it makes the intercepted traffic useless: they capture ciphertext, not credentials. This is why HTTPS and VPNs matter on untrusted networks.

Other defenses reduce the chance of getting on-path in the first place: strong wireless security, network segmentation, and detecting ARP anomalies.

Scenario

A victim logs in over HTTPS while an attacker is on-path. What does the attacker see?

Reveal answer

Encrypted traffic only. The attacker can see that communication is happening but cannot read the login, because TLS encrypts it in transit.

Real-world example

On-path attacks on open Wi-Fi

Researchers routinely demonstrate intercepting unencrypted traffic on open networks by getting on-path, often via ARP spoofing on a shared LAN. Encryption is what keeps the captured data useless.

Encryption protects the data, not the positioning.

Key Terms

Man-in-the-middle	An attacker positioned between two parties' traffic.
On-path	Another name for a man-in-the-middle position.
ARP spoofing	Common way to get on-path on a local network.
TLS	Encryption that makes intercepted traffic unreadable.

Match It Up

Tap a term, then tap its definition. Correct pairs lock in green.

Term

Definition

All matched. Nice work.

Common Mistakes

Thinking encryption blocks the interception

Encryption does not stop on-path positioning; it makes the captured data unreadable.

Forgetting ARP spoofing enables it on a LAN

On a local network, ARP spoofing is the common path to a man-in-the-middle position.

Assuming only Wi-Fi is vulnerable

Wired LANs are also vulnerable via ARP spoofing.

Ignoring traffic alteration

On-path attackers can change traffic, not just read it.

Check for Understanding

Predict your answer before you tap. Click a choice to check it and read why.

Question 1

A man-in-the-middle attack succeeds when the attacker:

B. An on-path attacker positions themselves between two parties to read or alter traffic.

Question 2 Predict first

On a local network, which attack commonly sets up a man-in-the-middle position?

B. ARP spoofing forges replies so both parties send traffic through the attacker.

Question 3

Why does TLS encryption help against on-path attacks?

A. Encryption does not prevent interception but makes the captured data useless to the attacker.

Question 4 Predict first

Which statements are true? I. On-path attackers can alter traffic. II. Encryption stops interception entirely. III. Wired LANs can be vulnerable.

A. I and III are true. II is false: encryption protects the data, not the positioning.

Question 5

An attacker on an open network reads a victim's plaintext login in transit. This is a:

D. Reading traffic between two parties in transit is a man-in-the-middle (on-path) attack.

Question 6

Besides encryption, what reduces the chance of an on-path attack?

C. Strong wireless security and segmentation make it harder for an attacker to get on-path.

Frequently Asked Questions

An attack where the adversary positions themselves between two communicating parties so they can read or alter the traffic passing between them.

On a local network, ARP spoofing tricks both parties into routing traffic through the attacker, which is how the attacker gets on-path.

Encryption does not stop the attacker from intercepting traffic, but it makes the captured data unreadable, so they gain ciphertext rather than credentials.

← PreviousNetwork Attacks Next →MAC Flooding

Keep studying

All Topics Unit 3 Study Guide Practice Questions

Get in Touch

Whether you're a student, parent, or teacher — I'd love to hear from you.

Typically responds within 24 hours

✓

Message Sent!

Thanks for reaching out. I'll get back to you within 24 hours.

Name *

Email *

I am a... (optional)

Which course? (optional)

Phone (optional)

How did you find us? (optional)

🏫 Welcome, fellow educator!

I offer curriculum resources, practice materials, and study guides designed for AP CS teachers. Let me know what you're looking for — whether it's classroom materials, a guest speaker, or Teachers Pay Teachers resources.

Message (optional — leave blank if just subscribing)

✉

[email protected]

📚

Courses

AP CSA, CSP, & Cybersecurity

⏱

Response Time

Within 24 hours

Prefer email? Reach me directly at [email protected]