Home Security Flaw in WPA2 protocol puts most Wi-Fi devices at risk
Flaw in WPA2 protocol puts most Wi-Fi devices at risk Featured

Belgian researcher Mathy Vanhoef of imec-DistriNet, KU Leuven has revealed details of a major flaw in the WPA2 protocol that is used for wireless security.

Vanhoef said tonight (Australian time) that attackers within range of a victim could exploit these weaknesses using key reinstallation attacks (KRACKs). (A detailed paper on the flaws is here.)

"Concretely, attackers can use this novel attack technique to read information that was previously assumed to be safely encrypted. This can be abused to steal sensitive information such as credit card numbers, passwords, chat messages, emails, photos, and so on," he wrote.

"The attack works against all modern protected Wi-Fi networks. Depending on the network configuration, it is also possible to inject and manipulate data. For example, an attacker might be able to inject ransomware or other malware into websites."

Vanhoef said the flaws were in the Wi-Fi standard itself, and not in individual products or implementations.

"Therefore, any correct implementation of WPA2 is likely affected. To prevent the attack, users must update affected products as soon as security updates become available," he wrote.

"Note that if your device supports Wi-Fi, it is most likely affected. During our initial research, we discovered ourselves that Android, Linux, Apple, Windows, OpenBSD, MediaTek, Linksys, and others, are all affected by some variant of the attacks."

Vanhoef said there was no need for a WPA3 implementation.

"No, luckily implementations can be patched in a backwards-compatible manner. This means a patched client can still communicate with an unpatched access point, and vice versa," he wrote

"In other words, a patched client or access points send exactly the same handshake messages as before, and at exactly the same moments in time. However, the security updates will assure a key is only installed once, preventing our attacks. So again, update all your devices once security updates are available."

The research behind the attack will be presented at the Computer and Communications Security conference, and at the Black Hat Europe conference, to be held from 30 October and 2 December respectively.

As a proof of concept, Vanhoef said he had carried out a key reinstallation attack against an Android smartphone.

"In this demonstration, the attacker is able to decrypt all data that the victim transmits. For an attacker this is easy to accomplish, because our key reinstallation attack is exceptionally devastating against Linux and Android 6.0 or higher," he wrote.

"This is because Android and Linux can be tricked into (re)installing an all-zero encryption key. When attacking other devices, it is harder to decrypt all packets, although a large number of packets can nevertheless be decrypted.

"In any case, the following demonstration highlights the type of information that an attacker can obtain when performing key reinstallation attacks against protected Wi-Fi networks."

The main attack that Vanhoef demonstrated was against the 4-way handshake of the WPA2 protocol that is executed when a client wants to join a protected Wi-Fi network.

It is used to confirm that both the client and access point possess the correct credentials (e.g. the pre-shared password of the network). Simultaneously, the 4-way handshake also negotiates a fresh encryption key that will be used to encrypt all subsequent traffic. All modern protected Wi-Fi networks use the 4-way handshake.

Explaining the attack, Vanhoef said in a key reinstallation attack, the adversary tricked a victim into reinstalling an already-in-use key.

"This is achieved by manipulating and replaying cryptographic handshake messages. When the victim reinstalls the key, associated parameters such as the incremental transmit packet number (i.e. nonce) and receive packet number (i.e. replay counter) are reset to their initial value.

"Essentially, to guarantee security, a key should only be installed and used once. Unfortunately, we found this is not guaranteed by the WPA2 protocol. By manipulating cryptographic handshakes, we can abuse this weakness in practice."

Well-known British security researcher Kevin Beaumont made a list of the takeaways from the detailed research paper. They were:

  • It is patchable, both client and server (Wi-Fi) side.
  • Linux patches are available now. Linux distributions should have it very shortly.
  • The attack doesn’t realistically doesn’t work against Windows or iOS devices. The Group vuln is there, but it’s not near enough to actually do anything of interest.
  • There is currently no publicly available code out there to attack this in the real world — you would need an incredibly high skill set and to be at the Wi-Fi base station to attack this.
  • Android is the issue, which is why the research paper concentrates on it. The issue with Android is people largely don’t patch.

The CVE identifiers assigned to track the products affected specific instantiations of the key reinstallation attack are given below:

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.

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Sam Varghese

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Sam Varghese has been writing for iTWire since 2006, a year after the sitecame into existence. For nearly a decade thereafter, he wrote mostly about free and open source software, based on his own use of this genre of software. Since May 2016, he has been writing across many areas of technology. He has been a journalist for nearly 40 years in India (Indian Express and Deccan Herald), the UAE (Khaleej Times) and Australia (Daily Commercial News (now defunct) and The Age). His personal blog is titled Irregular Expression.

 

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