Researchers have discovered a flaw in the Wi-Fi standard that attackers may use to eavesdrop on wireless network traffic even if WPA2 is used for protection.
Key Reinstallation Attacks, or Krack Attacks, work against all Wi-Fi networks protected by WPA2, and may in some cases be used to inject and manipulate data as well. The attack works against WPA and WPA2 standards, and against personal and Enterprise networks that implement Wi-Fi.
The attack method works against the 4-way handshake of the WPA2 protocol. This handshake is executed when client devices, say an Android smartphone or a laptop, want to join the Wi-Fi network.
The handshake verifies credentials and negotiates an encryption key that is then used to protect the traffic while the connection is active.
Update: Microsoft published advisory in which it highlighted that it fixed the issue for all supported and affected versions of Windows on this October 2017 Patch Tuesday.
The main flaw the researchers discovered affects the key, and is achieved by “manipulating and replying cryptographic handshake messages”. In other words, the attacker tricks the victim into reinstalling a key that is already in use.
When a client joins a network, it executes the 4-way handshake to negotiate a fresh encryption key. It will install this key after receiving message 3 of the 4-way handshake. Once the key is installed, it will be used to encrypt normal data frames using an encryption protocol. However, because messages may be lost or dropped, the Access Point (AP) will retransmit message 3 if it did not receive an appropriate response as acknowledgment. As a result, the client may receive message 3 multiple times. Each time it receives this message, it will reinstall the same encryption key, and thereby reset the incremental transmit packet number (nonce) and receive replay counter used by the encryption protocol.
We show that an attacker can force these nonce resets by collecting and replaying retransmissions of message 3 of the 4-way handshake. By forcing nonce reuse in this manner, the encryption protocol can be attacked, e.g., packets can be replayed, decrypted, and/or forged.
The researchers note that any data that is transferred can in theory by decrypted by the attacker.
The following Common Vulnerabilities and Exposures identifiers were assigned to the vulnerability:
- CVE-2017-13077: Reinstallation of the pairwise encryption key (PTK-TK) in the 4-way handshake.
- CVE-2017-13078: Reinstallation of the group key (GTK) in the 4-way handshake.
- CVE-2017-13079: Reinstallation of the integrity group key (IGTK) in the 4-way handshake.
- CVE-2017-13080: Reinstallation of the group key (GTK) in the group key handshake.
- CVE-2017-13081: Reinstallation of the integrity group key (IGTK) in the group key handshake.
- CVE-2017-13082: Accepting a retransmitted Fast BSS Transition (FT) Reassociation Request and reinstalling the pairwise encryption key (PTK-TK) while processing it.
- CVE-2017-13084: Reinstallation of the STK key in the PeerKey handshake.
- CVE-2017-13086: reinstallation of the Tunneled Direct-Link Setup (TDLS) PeerKey (TPK) key in the TDLS handshake.
- CVE-2017-13087: reinstallation of the group key (GTK) when processing a Wireless Network Management (WNM) Sleep Mode Response frame.
- CVE-2017-13088: reinstallation of the integrity group key (IGTK) when processing a Wireless Network Management (WNM) Sleep Mode Response frame.
The research paper can be downloaded from here (PDF), additional information on the vulnerability and the researchers on the Krack Attacks website.
Good news is that it is possible to patch the issue. However, a firmware update needs to be released by the manufacturer of the router, access point or client. The researchers note that any device that uses Wi-Fi is likely vulnerable to the attack.
One thing that users may do is use VPN connections to use an extra layer of protection so that attackers cannot decrypt the traffic even if they attack a device successfully. You may use cable connections as well if that is an option.
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