"Krack Attack" WPA2 protocol Wi-Fi attack: This is how the attack works

(c). bankinfosecurity.com

A vulnerability in the WPA2 protocol allowing attackers to read encrypted information transmitted over Wi-Fi was discovered by Mathy Vanhoef, a post-doctorate researcher at KU Leuven. Due to a flaw in the design of the protocol itself—not a specific vendor implementation—attackers can capture part of the handshake message, and use modified versions of that to trick devices into installing a blank encryption key, a process called "key reinstallation attacks," or KRACKs by Vanhoef.

How the attack works

Because of the depth and nuance of this vulnerability, collectively KRACK has 10 CVE identifiers assigned to it. The lynchpin of the vulnerability is the four-way handshake used when a client device attempts to join a protected network. After verifying the Wi-Fi password for the network itself, the encryption key for the session is negotiated. These handshake messages can be captured and manipulated by an attacker, and rebroadcast to a device which proceeds to reinstall the encryption key.

The WPA2 handshake design permits for the possibility of a dropped packet during handshake. Therefore, the third step of the four-way handshake—in which the encryption key is negotiated—may be rebroadcast to the client if the access point has not received an acknowledgement. Per protocol design, the client may receive the encryption key multiple times, and is expected to reinstall that key, resetting the incremental packet transit number ("nonce") and receive reply counter. Attackers can take advantage of this behavior to replay, decrypt, or forge packets.

Naturally, this ability extends to TCP SYN packets, making it possible for attackers to hijack TCP connections, in functionally the same way attackers inject data on unprotected Wi-Fi networks.

Of note, this attack does not allow attackers to recover the network password. (James Sanders, techrepublic.com)