Severe flaw in WPA2 protocol leaves Wi-Fi exposed

KRACK attack allows other nasties, including connection hijacking and malicious injection.

An air of unease set into the security circles on Sunday as they prepared for the disclosure of high-severity vulnerabilities in the Wi-Fi Protected Access II protocol that make it possible for attackers to eavesdrop Wi-Fi traffic passing between computers and access points.

The proof-of-concept exploit is called KRACK, short for Key Reinstallation Attacks. The research has been a closely guarded secret for weeks ahead of a coordinated disclosure that's scheduled for 8 a.m. Monday, east coast time. An advisory the US CERT recently distributed to about 100 organizations described the research this way:

"US-CERT has become aware of several key management vulnerabilities in the 4-way handshake of the Wi-Fi Protected Access II (WPA2) security protocol. The impact of exploiting these vulnerabilities includes decryption, packet replay, TCP connection hijacking, HTTP content injection, and others. Note that as protocol-level issues, most or all correct implementations of the standard will be affected. The CERT/CC and the reporting researcher KU Leuven, will be publicly disclosing these vulnerabilities on 16 October 2017."

According to a researcher who has been briefed on the vulnerability, it works by exploiting a four-way handshake that's used to establish a key for encrypting traffic. During the third step, the key can be resent multiple times. When it's resent in certain ways, a cryptographic nonce can be reused in a way that completely undermines the encryption.

A Github page belonging to one of the researchers and a separate placeholder website for the vulnerability used the following tags:

WPA2
KRACK
key reinstallation
security protocols
network security, attacks
nonce reuse
handshake
packet number
initialization vector
Researchers briefed on the vulnerabilities said they are indexed as: CVE-2017-13077, CVE-2017-13078, CVE-2017-13079, CVE-2017-13080, CVE-2017-13081, CVE-2017-13082, CVE-2017-13084, CVE-2017-13086, CVE-2017-13087, CVE-2017-13088. One researcher told Ars that Aruba and Ubiquiti, which sell wireless access points to large corporations and government organizations, already have updates available to patch or mitigate the vulnerabilities.

The vulnerabilities are scheduled to be formally presented in a talk titled Key Reinstallation Attacks: Forcing Nonce Reuse in WPA2 scheduled for November 1 at the ACM Conference on Computer and Communications Security in Dallas. It's believed that Monday's disclosure will be made through the site krackattacks.com. The researchers presenting the talk are Mathy Vanhoef and Frank Piessens of KU Leuven and imec-DistriNet, Maliheh Shirvanian and Nitesh Saxena of the University of Alabama at Birmingham, Yong Li of Huawei Technologies in Düsseldorf, Germany, and Sven Schäge of Ruhr-Universität Bochum in Germany. The researchers presented this related research in August at the Black Hat Security Conference in Las Vegas.

The vast majority of existing access points aren't likely to be patched quickly, and some may not be patched at all. If initial reports are accurate that encryption bypass exploits are easy and reliable in the WPA2 protocol, it's likely attackers will be able to eavesdrop on nearby Wi-Fi traffic as it passes between computers and access points. It might also mean it's possible to forge Dynamic Host Configuration Protocol settings, opening the door to hacks involving users' domain name service.

It wasn't possible to confirm the details reported in the CERT advisory or to assess the severity at the time this post was going live. If eavesdropping or hijacking scenarios turn out to be easy to pull off, people should avoid using Wi-Fi whenever possible until a patch or mitigation is in place. When Wi-Fi is the only connection option, people should use HTTPS, STARTTLS, Secure Shell and other reliable protocols to encrypt Web and e-mail traffic as it passes between computers and access points. As a fall-back users should consider using a virtual private network as an added safety measure, but users are reminded to choose their VPN providers carefully, since many services can't be trusted to make users more secure. This post will be updated as more information becomes available.