Attacking Legacy Wi-Fi | TryHackMe Walkthrough

Room: Attacking Legacy Wi-Fi
Difficulty: Medium
Estimated time: 150 minutes

Introduction

This room is about attacking older Wi-Fi security, mainly WEP and WPS.

I already knew that WEP was outdated, but I had never really gone through the process of breaking it myself. The room covers a few different techniques, starting with capturing wireless traffic and recovering a WEP key, then moving on to attacks against clients and WPS.

There are quite a few steps, so I’ll go through what I did and explain what was happening along the way.

1. Breaking WEP

The first part focuses on recovering a WEP key.

WEP uses RC4 to encrypt wireless traffic. The problem is how it handles its initialization vectors, also called IVs. These IVs are sent in clear text and are too small to provide enough uniqueness. When enough packets are captured, patterns in the data can be used to recover the key.

I started by putting the wireless interface into monitor mode and checking which networks were available.

airmon-ng

After identifying the correct wireless interface, I enabled monitor mode:

airmon-ng start wlan0

I then used airodump-ng to look for nearby wireless networks:

airodump-ng wlan0mon

Once I found the target network, I started capturing its traffic:

airodump-ng --bssid [TARGET_BSSID] -c [CHANNEL] -w capture wlan0mon

The goal was to collect enough packets and IVs to make key recovery possible.

After collecting enough traffic, I used aircrack-ng:

aircrack-ng capture-01.cap

Aircrack-ng analyses the captured packets and attempts to recover the WEP key using statistical attacks.

The important part here is that the attack does not need to guess every possible key. It uses weaknesses in WEP’s implementation to narrow down the possibilities.

2. Understanding the WEP encryption

The next part goes deeper into how WEP actually works.

WEP combines a secret key with a 24-bit initialization vector to generate an RC4 keystream. The keystream is then XORed with the data to encrypt it.

WEP also uses CRC32 as an integrity check. However, CRC32 is not a cryptographic integrity mechanism, which makes it possible to manipulate encrypted packets without knowing the secret key.

This is where the bit-flipping attack comes in.

By changing specific bits in an encrypted packet, an attacker can make predictable changes to the decrypted data. Because CRC32 is linear, the integrity value can also be adjusted.

I found this part useful because it explains why WEP is vulnerable beyond just having a weak key recovery process.

3. Fragmentation attacks

Another technique covered in the room is packet fragmentation.

The idea is to use a captured packet to obtain information about the keystream. If the attacker can recover enough of the keystream, it can be used to construct and inject new packets.

This is useful because it can help generate more wireless traffic, which can then be captured and analysed.

The general process is to capture suitable packets, use fragmentation to recover keystream material, and then use that information to inject traffic.

It is another example of how weaknesses in WEP can be combined to make an attack more effective.

4. Caffe Latte attack

The Caffe Latte attack is interesting because it does not require the attacker to be connected to the wireless network.

Instead, it targets a client that is already configured to connect to a WEP network.

The attacker captures traffic from the client and manipulates it to make the client send encrypted packets. Those packets can then be used to recover information about the WEP key.

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This is especially useful in situations where the access point itself is not within range, but a client connected to the network is.

The main thing to understand is that the attack targets the client rather than directly attacking the access point.

5. Connecting to the WEP network

After recovering the WEP key, the next step is to connect to the wireless network.

I used the recovered key when configuring the wireless connection.

The exact command depends on the interface and network configuration, but the general idea is to connect using the target’s SSID and recovered WEP key.

Once connected, I could verify that the key worked and that the network was accessible.

This was a good way to confirm that the previous key recovery steps had actually worked.

6. Offline brute force

The room also demonstrates an offline brute force attack.

Brute forcing WEP directly can take a long time if the keyspace is large. However, once some information about the key is available, the number of possible combinations can be reduced.

Instead of testing every possible key against the live network, the attacker can work with captured data offline.

That makes the process easier to control and avoids repeatedly interacting with the wireless network.

The important part is reducing the keyspace before starting the brute force. Without that, the attack can become unnecessarily slow.

7. Attacking WPS

The final part focuses on WPS.

WPS was designed to make connecting devices to a wireless network easier. One common method uses an eight digit PIN.

The problem is that some implementations allow attackers to test PIN combinations in a way that makes the process much easier than guessing a normal wireless password.

The room introduces two approaches: Pixie Dust and an online Reaver attack.

Pixie Dust

Pixie Dust is an attack against weaknesses in certain WPS implementations.

Instead of trying every possible PIN, it uses information obtained during the WPS exchange to calculate the PIN offline.

I tried the technique in the room, but it did not successfully recover the PIN in this case.

That does not mean Pixie Dust is useless. It depends heavily on the router’s WPS implementation and whether it is vulnerable to the attack.

Reaver

The next technique uses Reaver to interact with the access point and attempt to recover the WPS PIN.

The basic command looks like this:

reaver -i wlan0mon -b [TARGET_BSSID] -vv

Reaver sends WPS PIN attempts to the access point and checks its responses.

Unlike Pixie Dust, this is an online attack because it communicates directly with the target. Depending on the router, it can take a long time, and some devices have protections such as PIN lockout.

In the room, I used Reaver to complete the WPS task and retrieve the required information.

What I learned

This room gave me a better understanding of why older wireless security protocols are dangerous.

Before doing the room, I knew WEP and WPS were outdated, but I had not worked through the actual attacks. Seeing how packet capture, IV analysis, fragmentation, client attacks and brute force can be combined made the weaknesses much clearer.

The WPS section was also useful because it showed that even when a wireless password is strong, another feature on the router can still create a weakness.

The main takeaway: WEP should not be used, and WPS should be disabled when it is not needed. Modern wireless networks should use WPA2 or WPA3 with a strong password.

Room completion

Room: Attacking Legacy Wi-Fi
Status: Completed

The room covered several different wireless attacks, and it was a good introduction to how attackers can exploit older Wi-Fi protocols.

It was especially useful to see the difference between recovering a WEP key through captured traffic and attacking WPS through the PIN mechanism.