The week started with terrible news for users, companies, and security experts alike: a new study has exposed high-profile vulnerabilities in the WPA2 protocol, with a proof of concept allowing data interception on a protected WiFi network. The good news is that these vulnerabilities can be eliminated with the right updates. The bad news is that updates must reach all our devices, including routers, and we already know how manufacturers tend to behave…
What happened?
Researchers Mathy Vanhoef and Frank Piessens published on Sunday night a study exploring a new attack technique that affects the WPA2 protocol. Dubbed KRACK (short for Key Reinstallation AttaCK), the technique relies on a chain of vulnerabilities that, while recognized in the security world and declared as 'possible' to implement despite their difficulty, were turned into a proof of concept. They confirmed that essentially every device relying on WPA2 is at risk.
"All" devices?
The information mentions OS X 10.9.5, macOS Sierra 10.12, iOS 10.3.1 or higher, three versions of the wpa_supplicant implementation, Android 6.0 and above, OpenBSD 6.1, Windows 7, Windows 10, and hardware from brands like Linksys and MediaTek, but it doesn't rule out affecting more platforms. iOS and Windows are the two operating systems with the most resistance to the attack. Microsoft confirmed that the necessary fixes were published with the last round of patches on October 10th. Apple has already done the same in the beta versions of its environments and will take a couple more weeks. Linux is in a similar situation, with patches released and awaiting integration into the distros. The main problem lies with Android. The researchers note that KRACK is “particularly devastating” against Android 6.0. Google is working on a hotfix, but it's already estimated that (at least) 40 percent of Android devices, and many of them, may never receive it.
How exactly does it work?
WiFi networks use a series of shared keys to protect the traffic flowing through them. The most popular (and recommended) encryption is AES, but there are other less secure variants. Keys are shared through 'handshakes' that verify clients' identities. KRACK's job is to throw itself headlong against the so-called 'four-way handshake'. With precise manipulation of the handshake messages, the attacker causes the victim to reinstall an already used key. Keys are supposed to be single-use, but the WPA2 protocol doesn't guarantee that. The depth of KRACK depends on the handshake type: For AES-CCMP, the attacker can replay and decrypt packets. If it's WPA-TKIP or GCMP (Galois/Counter Mode Protocol), the capability extends to replay, decryption, and forging packets.
Now, in plain English
In very relaxed terms, KRACK allows intercepting, reading, and in some cases modifying traffic on a network protected with WPA2 without knowing the WiFi password. That doesn't mean WPA2 is broken or anything close. Fortunately, implementations and clients can receive patches with backward compatibility, so we don't need an emergency 'WPA3'. If we add the detail that it's not easy for an attacker to deploy the attack (it requires, among other things, being near the network), the odds are in our favor. However…
What about routers?
The general recommendation is to look for firmware updates for them. The problem is that most devices are in a similar trap to Android smartphones, and their manufacturers will simply ignore any update requests. The official KRACK page insists that the attack doesn't focus on access points but on the four-way handshake. The average user's priority should be updating clients (computers, tablets, smartphones). A good step to minimize the impact of KRACK on routers is not using them as repeaters and disabling the support for fast roaming 802.11r.
TVs, printers, Internet of Things?
They are also vulnerable clients. You'd like to think manufacturers will act responsibly and release patches for all their products, but real life has taught us otherwise.
How do we protect ourselves?
Without including updates, the first line of defense is using HTTPS whenever possible. Even if a KRACK attack manages to intercept router traffic, HTTPS is enough to obscure its content. Of course, there are specific tools that decrypt HTTPS packets, but the idea is to put obstacles in the attacker's path. Another option is adopting a robust VPN service, and by that I mean a paid solution. Not all VPNs do their job well, so we must closely study the offers. In summary: A WPA2 network compromised with KRACK shares the profile of a free, open network. It's hostile territory, but with proper precautions, we'll be well. We'll continue to follow the evolution of KRACK, don't go away.
