Exploiting Research Vulnerability

The WPA2 protocol has a critical vulnerability known as Key Reinstallation Attacks (KRACs) that allows attackers to access private encrypted information, inject and manipulate data for malicious means. The attack works by reinstalling an already-in-use cryptographic key through manipulation of the 4-way handshake protocol. Unpatched WPA2 networks are vulnerable to this attack, which has severe implications for data privacy.

Exploit Research
Deliverable
Executive Summary
Key Reinstallation Attacks (KRACs)
Most of the modern Wi-Fi networks is protected by the WPA2 protocol. It was recently discovered that
the WPA2 protocol had a critical vulnerability that can be exploited using a method known as Key
Reinstallation Attacks or “KRACs”. This method allows attackers to access private encrypted information,
as well as inject and manipulate data for malicious means. This vulnerability was discovered in the WPA2
standard as well, therefore affecting all unpatched Wi-Fi networks running on WPA2 protocol. KRACS
attacks a vulnerability within the 4 way WPA2 handshake that connects a user to the Wi-Fi network.
Currently almost all the Wi-Fi networks in use employ this protocol, thus making virtually every
unpatched Wi-Fi network vulnerable to this attack. The attack works by reinstalling an already in use
cryptographic key through a manipulation of the handshake protocol. Unpatched WPA2 protocol allows
the key to be replayed, which in turn resets the values within the handshake protocol and allows
attacker to obtain, decrypt and even forge packets between the client and the server. This is a critical
vulnerability that has severe implications for data privacy and has a potential to compromise an entire
network if the WPA2 access points are left unpatched.
Technical Description
Exploitation Description
Key reinstallation attacks work by tricking a victim into installing an already-in-use key through
manipulating and replaying cryptographic handshake protocols. When a client attempts to connect to
the Wi-Fi network, the client and the Wi-Fi access point perform a 4-way handshake in order to create
an encryption key. This key is installed by both the client and the access point after the client receives 3rd
message of the 4-way handshake. The 4-way handshake is part of an asymmetric encryption protocol
that allows 2 users to share an encryption key over an unsecured network through a process known as a
“Diffie-Hellman Key Exchange”. After the key is installed, it is used to encrypt and decrypt data between
the client and the access point. When the WPA2 protocol was designed, it was based on many concepts
that were used by the TCP/IP protocol. One of those protocols was the redundancy of packets in case
they were lost, dropped or corrupted. This also applies to packets sent and received during the 4-way
handshake. When the access point does not receive an ACK reply after the 3rd packet of the handshake,
it will retransmit that message, therefore the client may receive the 3rd handshake packet multiple
times. Every time the client receives that packet, it will reinstall the same encryption key. Reinstalling
the key resets all the associated parameters such as the replay counter and the incremental transmit
packet number to their initial value, thereby allowing the attacker to replay, decrypt and forge packets
in transit. This weakness is the result of the flaw in WPA2 protocol that allows an attacker to use a
cryptographic key more than once through manipulation of cryptographic handshakes. Several other key
exchange protocols have been shown to be vulnerable to this type of attack as well.
Attack Vector
The attack vector for the key reinstallation attacks is always the connection between the client and the
Wi-Fi access point. The attacker will likely try to manipulate the 4-way handshake protocol in order to

reinstall the encryption key as mentioned above. The objective of this is to attempt to decrypt a TCP SYN
packet, which will allow the attacker to learn counter and incremental sequence number of the packet
in order to hijack the TCP stream and inject malicious data or replay packets potentially comprising
private information. Decryption of the TCP packets is possible because key reinstallation attacks reset
initialization vectors of the TCP packets to their original value, this forces the WPA2 encryption protocol
to reuse the key stream. When the initialization of the key stream is known, then it is possible for the
attacker to decrypt packets with the same initialization vector. Once the TCP stream is hijacked, it
essentially becomes a man-in-the-middle attack. From here, depending on the protocol the attacker can
decrypt and forge packets towards both to the client and from the client. “The direction in which
packets can be decrypted (and possibly forged) depends on the handshake being attacked. Simplified,
when attacking the 4-way handshake, we can decrypt (and forge) packets sent by the client. When
attacking the Fast BSS Transition (FT) handshake, we can decrypt (and forge) packets sent towards the
client”1.
Mitigations
 Switch to AES CCMP encryption protocols for all Wi-Fi access points: This will ensure that the
vulnerability in question will not be used to inject packets into the data stream.
 Use HTTPS for everything: HTTPS creates application level encryption, which the vulnerability in
question does not affect. All the data transmitted under the HTTPS protocol will remain
encrypted.
 Turn firewalls on: Firewalls are essential to every cybersecurity solution. It is a mitigating factor
for countless of vulnerabilities.
 Use VPN if possible: Another application layer security that is independent of Wi-Fi
vulnerabilities. Just like HTTPS, it will ensure that Application layer data remain encrypted.
 Have an antivirus: This adds another layer of protection needed in modern cybersecurity
environment.
Remediation
 Turn automatic updates on: As the vulnerability was discovered, Microsoft immediately
announced that it will start working on the patch.
 Use wired connection: You won’t have Wi-Fi vulnerabilities if you don’t have Wi-Fi.
 If for whatever reason the vulnerability wasn’t patched, then don’t use Wi-Fi.
 Switch to WPA3: having the latest hardware that’s running on the latest protocols is a great way
to mitigate cyber threats.
 Contract a Penetration tester to check all Wi-Fi systems for this vulnerability, if they are
vulnerable then take them offline immediately.
1 M. Vanhoef, “Key Reinstallation Attacks,” KRACK Attacks: Breaking WPA2. [Online]. Available:
https://www.krackattacks.com/#paper

Exploitation Scenario2
The attacker will scan the network that he wants to attack and then he will clone the network on a
different channel. The attacker will use the cloned network to manipulate the 4-way handshake
messages in order to facilitate the key reinstallation attack. This will create a man-in-the-middle attack
where all the information is passed through the clone network that the victim thinks is the real network.
To get the victim onto the clone network, the attack will use special Wi-Fi frames that will force the
victim’s machine to switch to the clone network. In the meantime, the attacker will use an ssl strip tool
in order to make sure that the victim does not use HTTPS. Next the attacker executes the key
reinstallation attack which allows the attacker to obtain the encryption key and reset the initialization
vector. Now the attacker can decrypt the tcp packet(s) and take control of the TCP stream, which will
allow the attacker to inject malicious packets to or from the client.
References
1. M. Vanhoef and F. Piessens, “Key Reinstallation Attacks,” Proceedings of the 2017 ACM SIGSAC
Conference on Computer and Communications Security - CCS 17, 2017.
2. “KRACK: What to know and 8 ways to mitigate this new cyber attack,” Medium, 25-Oct-2017.
[Online]. Available: https://medium.com/pluralsight/krack-cyber-attack-e234be907b21.
3. M. Vanhoef, “Key Reinstallation Attacks,” KRACK Attacks: Breaking WPA2. [Online]. Available:
https://www.krackattacks.com/#paper.
4. F. Donoso, “Key Reinstallation Attacks (KRACK) affecting WPA Protocol – Advisory,” Key
Reinstallation Attacks (KRACK) affecting WPA Protocol – Advisory, 23-Jan-2018. [Online].
Available: https://research.kudelskisecurity.com/2017/10/16/key-reinstallation-attacks-krack-
affecting-wpa-protocol-advisory/
2 M. Vanhoef, “Key Reinstallation Attacks,” KRACK Attacks: Breaking WPA2. [Online]. Available:
https://www.krackattacks.com/#paper