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Network card rootkit offers extra stealth

Sneaky reverse engineering

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Security researchers have demonstrated how it might be possible to place backdoor rootkit software on a network card.

Guillaume Delugré, a reverse engineer at French security firm Sogeti ESEC, was able to develop proof-of-concept code after studying the firmware from Broadcom Ethernet NetExtreme PCI Ethernet cards.

He used publicly available documentations and open source tools to develop a firmware debugger. He also reverse-engineered the format of the EEPROM where firmware code is stored, as well as the bootstrap process of the device.

Using the knowledge gained from this process, Delugré was able to develop custom firmware code and flash the device so that his proof-of-concept code ran on the CPU of the network card. The technique opens the possibility of planting a stealthy rootkit that lives within the network card, an approach that gives potential miscreants several advantages over conventional backdoors.

Chief among these is that there will be no trace of the rootkit on the operating system, as it is being hidden inside the network interface card.

"The network card natively needs to perform Direct memory access (DMA) accesses, so that network frames can be exchanged between the driver and the device," Delugré explains.

"From the firmware point of view, everything is operated using special dedicated device registers, some of them being non-documented. An attacker would then be able to communicate remotely with the rootkit in the network card and get access to the underlying operating system thanks to DMA."

Delugré gave a presentation on his research at the hack.lu conference last month. A write-up of his research, along with slides on his presentation and a demo, was published on Sunday here. ®

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