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Flaw in 802.11n Standard Exposes Wireless Networks to Attacks: Researchers

A vulnerability in the 802.11n wireless networking standard can be exploited by a remote attacker to target wireless networks, researchers have warned.

Introduced in 2009, the 802.11n standard is designed to increase the speed of wireless networks, improve their reliability and security, and extend the range of wireless transmissions. This version introduces a frame aggregation mechanism to the media access control (MAC) layer that increases throughput by sending two or more data frames in a single transmission.

According to researchers from the Expertise Centre for Digital Media at the Hasselt University in Belgium, the frame aggregation mechanism in 802.11n is plagued by a vulnerability that can be exploited via a technique called Packet-In-Packet (PIP) to inject arbitrary frames into wireless networks. This allows an attacker to interact with services on the internal network.

The experts say such attacks work against almost any modern Wi-Fi chipset as long as the target is connected to an open network. They have also pointed out that the attack can be launched without being in proximity of the targeted wireless networks and without requiring a wireless interface card.

An attacker can leverage this technique to deauthenticate clients, inject malicious beacon frames, perform host and port scans, bypass firewall rules, and conduct Address Resolution Protocol (ARP) spoofing. In some cases, the attacker needs to know the MAC address of the targeted access point, researchers said.

“As a practical example, you could upload an image to imgur (as long as the service does not compress the images; this would change the data) and send a link of the image to a victim,” one of the experts involved in this research explained in a post on Reddit. “Downloading the image would then result in frames being injected on the network as long as the network is open and supports aggregation.”

The researcher has pointed out that the malicious frames can be embedded in any type of payload, including videos, as long as they are not modified before being sent to the target.

According to researchers, there are several methods that can be used by network administrators to mitigate such injection attacks. The list includes the use of MAC layer encryption, disabling Aggregated Mac Protocol Data Unit (A-MPDU) frame aggregation, configuring the system to drop corrupted A-MPDUs, the use of Language-theoretic security (LangSec) stacks, modulation switching, and the use of deep packet inspection.

A proof-of-concept (PoC) implementation of this attack and the complete research paper are available online.

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Eduard Kovacs (@EduardKovacs) is a contributing editor at SecurityWeek. He worked as a high school IT teacher for two years before starting a career in journalism as Softpedia’s security news reporter. Eduard holds a bachelor’s degree in industrial informatics and a master’s degree in computer techniques applied in electrical engineering.