New Kr00k vulnerability lets attackers decrypt WiFi packets

Kr00k affects devices using Broadcom and Cypress Wi-Fi chips.
Written by Catalin Cimpanu, Contributor

Today, at the RSA 2020 security conference in San Francisco, security researchers from Slovak antivirus company ESET will present details about a new vulnerability that impacts WiFi communications.

Named Kr00k, this bug can be exploited by an attacker to intercept and decrypt some type of WiFi network traffic (relying on WPA2 connections).

According to ESET, Kr00k affects all WiFi-capable devices running on Broadcom and Cypress Wi-Fi chips. These are two of the world's most popular WiFi chipsets, and they are included in almost everything, from laptops to smartphones, and from access points to smart speakers and other IoT devices.

ESET researchers said they personally tested and confirmed that Kr00k impacts devices from Amazon (Echo, Kindle), Apple (iPhone, iPad, MacBook), Google (Nexus), Samsung (Galaxy), Raspberry (Pi 3) and Xiaomi (Redmi), but also access points from Asus and Huawei.

In a press release today, ESET said it believes that more than a billion devices are vulnerable to Kr00k, and they consider this number "a conservative estimate."

What's Kr00k?

At the technical level [PDF], Kr00k is just a bug, like many other bugs that are being discovered on a daily basis in the software that we all use.

The difference is that Kr00k impacts the encryption used to secure data packets sent over a WiFi connection.

Typically, these packets are encrypted with a unique key that depends on the user's WiFi password. However, ESET researchers say that for Broadcom and Cypress Wi-Fi chips, this key gets reset to an all-zero value during a process called "disassociation."

Image: ESET

Disassociation is something that occurs naturally in a WiFi connection. It refers to a temporary disconnection that usually happens due to a low WiFi signal.

WiFi devices enter into disassociated states many times a day, and they're automatically configured to re-connect to the previously used network when this happens.

ESET researchers say that attackers can force devices into a prolonged disassociated state, receive WiFi packets meant for the attacked device, and then use the Kr00k bug to decrypt WiFi traffic using the all-zero key.

kr00k attack
Image: ESET

This attack scenario allows hackers to actively intercept and decrypt WiFi packets, normally considered to be secure.

The good news is that the Kr00k bug only impacts WiFi connections that use WPA2-Personal or WPA2-Enterprise WiFi security protocols, with AES-CCMP encryption.

This means that if you use a device with a Broadcom or Cypress WiFi chipset, you can protect yourself against attacks by using the newer WPA3 WiFi authentication protocol.

Patches should be already available for most devices by now

Furthermore, ESET has also worked during the past months to responsibly disclose the Kr00k bug to Boadcom, Cypress, and all other impacted companies.

"According to some vendor publications and our own (non-comprehensive) tests, devices should have received patches for the vulnerability by the time of publication," ESET researchers said today.

"Depending on the device type, this might only mean ensuring the latest OS or software updates are installed (Android, Apple and Windows devices; some IoT devices), but may require a firmware update (access points, routers and some IoT devices)."

Users can check if they received Kr00k patches by checking their device OS/firmware changelogs for fixes against CVE-2019-15126, which is the unique ID assigned to track this bug.

However, one important point about Kr00k is that the bug does not lead to a full compromise of a user's communications. The bug can be exploited to break the encryption used to secure the WiFi channel. If the user's original communications were also encrypted -- such as accessing websites via HTTPS, using Tor, or encrypted IM clients -- then those communications would still remain encrypted even after a Kr00k attack.

Furthermore, the bug cannot be used part of automated botnet attacks, requires physical proximity to a victim (WiFi network range), and Kr00k cannot retrieve large and long-winded communications streams without the user noticing problems with their WiFi communications.

Not as bad as KRACK

All in all, the Kr00k vulnerability should be easier to protect against than KRACK -- a major vulnerability that impacted the WPA2 WiFi protocol and forced most device vendors to switch to using WPA3 by default.

A new KRACK attack, named Dragonblood, was later discovered to impact even some newer WPA3 connections, but this newer attack didn't impact the entire WiFi ecosystem as the original KRACK attack did.

ESET researchers said they discovered Kr00k while looking into the devastating effects of the KRACK attack; however, the two -- KRACK and Kr00K -- should not be considered the same.

Image: ESET

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