A Flaw in Billions of Wi-Fi Chips Let Attackers Decrypt Data

Billions of devices—many of them already patched—are affected by a Wi-Fi vulnerability that allows nearby attackers to decrypt sensitive data sent over the air, researchers said on Wednesday at the RSA security conference.

ARS TECHNICA

This story originally appeared on Ars Technica, a trusted source for technology news, tech policy analysis, reviews, and more. Ars is owned by WIRED’s parent company, Condé Nast.

The vulnerability exists in Wi-Fi chips made by Cypress Semiconductor and Broadcom, the latter a chipmaker Cypress acquired in 2016. The affected devices include iPhones, iPads, Macs, Amazon Echos and Kindles, Android devices, and Wi-Fi routers from Asus and Huawei, as well as the Raspberry Pi 3. Eset, the security company that discovered the vulnerability, said the flaw primarily affects Cypress’ and Broadcom’s FullMAC WLAN chips, which are used in billions of devices. Eset has named the vulnerability Kr00k, and it is tracked as CVE-2019-15126.

Manufacturers have made patches available for most or all of the affected devices, but it’s not clear how many devices have installed the patches. Of greatest concern are vulnerable wireless routers, which often go unpatched indefinitely.

“This results in scenarios where client devices that are unaffected (either patched or using different Wi-Fi chips not vulnerable to Kr00k) can be connected to an access point (often times beyond an individual’s control) that is vulnerable,” Eset researchers wrote in a research paper published on Wednesday. “The attack surface is greatly increased, since an adversary can decrypt data that was transmitted by a vulnerable access point to a specific client (which may or may not be vulnerable itself).”

A Key Consisting of All Zeros

Kr00k exploits a weakness that occurs when wireless devices disassociate from a wireless access point. If either the end user device or the access point is vulnerable, it will put any unsent data frames into a transmit buffer and then send them over the air. Rather than encrypt this data with the session key negotiated earlier and used during the normal connection, vulnerable devices use a key consisting of all zeros, a move that makes decryption trivial.

Disassociation typically happens when a client device roams from one Wi-Fi access point to another, encounters signal interference, or has its Wi-Fi turned off. Hackers within range of a vulnerable client device or access point can easily trigger disassociations by sending what’s known as management frames, which aren’t encrypted and require no authentication. This lack of security allows an attacker to forge management frames that manually trigger a disassociation.

With the forced disassociation, vulnerable devices will typically transmit several kilobytes of data that’s encrypted with the all-zero session key. The hacker can then capture and decrypt the data. Eset researcher Robert Lipovsky told me hackers can trigger multiple disassociations to further the chances of obtaining useful data.

Eset researchers determined that a variety of devices are vulnerable, including the following:

  • Amazon Echo 2nd gen
  • Amazon Kindle 8th gen
  • Apple iPad mini 2
  • Apple iPhone 6, 6S, 8, XR
  • Apple MacBook Air Retina 13-inch 2018
  • Google Nexus 5
  • Google Nexus 6
  • Google Nexus 6S
  • Raspberry Pi 3
  • Samsung Galaxy S4 GT-I9505
  • Samsung Galaxy S8
  • Xiaomi Redmi 3S

The researchers also found that the following wireless routers are vulnerable:

  • Asus RT-N12
  • Huawei B612S-25d
  • Huawei EchoLife HG8245H
  • Huawei E5577Cs-321

An Apple spokesman said the vulnerabilities were patched last October with details for macOS here and for iOS and iPadOS here.

Manufacturers of other vulnerable devices that still receive patch support couldn’t immediately be reached for comment.

The researchers tested Wi-Fi chips from other manufacturers, including Mediatek, Ralink, Realtek, and Qualcomm, and found no evidence any of them were vulnerable. Since it was impossible for the researchers to test all devices, it’s possible that other devices using Cypress and Broadcom chips are also affected.

While the vulnerability is interesting and users should make sure their devices are patched quickly—if they aren’t already—there are a few things that minimize the real-world threat posed. For one thing, most sensitive communications in 2020 are already encrypted, usually with the transport layer security protocol or by other methods. A glaring exception to this is domain name lookups, which, unless a computer is using DNS over HTTPS or DNS over TLS, are sent entirely over plaintext. Hackers who viewed these requests would be able to learn what domain names users were accessing.



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