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Bug-hunters punch huge holes in WPA3 standard for Wi-Fi security

Passwords, personal information can be sussed out by attackers during handshakes

Researchers have detailed a set of side-channel and downgrade attacks that potentially allow an attacker to compromise Wi-Fi networks equipped with WPA3 protections.

Mathy Vanhoef, of New York University Abu Dhabi, and Eyal Ronen, of Tel Aviv University, have disclosed five different methods for breaking into or disrupting routers using the newest version of the wireless network security standard. The duo have already privately reporting the issue to the Wi-Fi Alliance and Cert/CC to make sure vendors had time to get fixes out prior to disclosure.

Specifically, the duo found a number of ways an attacker can game the Dragonfly handshake system WPA3 uses to authenticate devices on a network. If exploited, this would allow the attacker to log into the target network without knowing the password.

"Concretely, attackers can then read information that WPA3 was assumed to safely encrypt," Vanhoef and Ronen explained. "This can for example be abused to steal sensitive information such as credit cards, passwords, chat messages, emails, and so on, if no extra protection such as HTTPS is used."

Side-channel bugs: not just for CPUs any more

Two of the issues posed were side channel attacks and have been classified together as CVE-2019-9494. Both describe ways for an attacker to use a dictionary attack to work out a password (the researchers estimate this can be done with AWS instances for about $125).

The first method is a timing-based attack that is based on how long the router takes to respond to commit frames. In some routers, the commit time is directly related to the password being used for the network. If an attacker know the exact time the router took to process the password, that person could simulate login attempts repeatedly in a virtualized environment until coming up with the password that required exact same response time.

"When the AP uses security groups based on elliptic curves, which all WPA3 devices are required to support, no timing information is leaked," Vanhoef and Ronen said. "However, when the AP supports the optional multiplicative security groups modulo a prime (MODP groups), the response time depends on the password being used."

The second side-channel method involves observing the memory access patterns of the router as it processes the password. As with the timing-based attack, a bad guy who was able to see the memory access pattern could then run a dictionary attack on another system until the discovery of the exact sequence that created the same pattern.

"Observing these patterns is possible if the adversary controls any application on the victim's device, and may even be possible when the adversary controls JavaScript code in the victim's browser," the bug-hunters explained.

Downgrade attacks use WPA3's shiny new status as a weapon

The other methods the researchers uncovered were a set of downgrade attacks that allow the attacker to force the router into tossing out WPA3 and using the older (and crackable) WPA2 standard.

The first attack is more of a social engineering trick plays on the "Transition mode" feature in WPA3 that allows backwards compatibility with WPA2. Because the transition mode is designed to allow both newer WPA3 and older WPA2-only devices to use the same password, the attacker could set up a lookalike network on WPA2. When a victim tried to log on to that network, the authentication would fail, but the handshake attempt would give the attacker enough information to then brute-force WPA2 to obtain the password for the target network.

The second downgrade attack likewise uses the spoofed network, and takes advantage of the "security group" component that allows the access point to tell the client device what security standard it wants to use. In this attack, the attacker-controlled access point would send the victim decline messages to not to use WPA3, requiring another attempt to send login credentials with WPA, once again allowing the attacker to brute-force the login.

And a DoS bug just for good measure

The final vulnerability plays on the technical sophistication of the Dragonfly handshake and the demand it places on access points. Quite simply, most hardware is only able to deal with around 16 commit frames per second.

"Processing this frame and generating an answer is computationally expensive, especially if defenses against (already known) side-channel attacks are implemented," the pair explain.

"Although WPA3 contains a cookie-exchange method to prevent attackers from forging commit frames using fake MAC addresses, it is trivial to bypass."

In other words, an attacker who could spoof these commit frames (this can be done without needing the password) would then be able to lock up the access point, and create a denial of service.

One more bug in the pipeline

Finally, Vanhoef and Ronen say they have one last bug, a way to crack EAP-PWD passwords, that they are holding off on releasing any details for until vendors and network admins have more time to update their routers and access points.

The rest of the bugs are explained in full detail in the duo's academic paper, "Dragonblood: A Security Analysis of WPA3's SAE Handshake" ®

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