Saturday, September 15, 2018

What Else is your Fax Machine Doing?

Researchers Eyal Itkin and Yaniv Balmas revealed a new type of vulnerability at Defcon 2018 – one which attacks your fax machine. They call this new exploit ‘Faxploit’ and demonstrated how a victim’s network could be infiltrated by sending a malicious fax to a certain model of networked fax machines over a normal phone line connection. By utilizing vulnerabilities, they discovered they could take over the machine and use it as a jump point into the internal network. After an impressive amount of reverse engineering utilizing existing exploits to load a debugger onto the target fax machine, the two researchers discovered additional vulnerabilities which could be used for a device takeover attack.
The vulnerability used in their demonstration relates to the embedded JPEG image parser on the device, normally used when receiving or sending colored faxes. By sending specially crafted JPEG headers to the machine they could trigger a stack based buffer overflow in the header parser and run arbitrary code on the device. Once they discovered the vulnerability in the fax handling mechanism of the device it was time to write an exploit to take advantage of it. They discovered that when the device received a JPEG it simply dumped the contents to a file with no validation. Due to this flaw they were able to store the exploit entirely inside of a specially crafted JPEG, achieving persistence due to it being written to the disk. When they wanted to perform tasks that needed additional input they could simply read from the file sitting on disk.
Their finished exploit implemented 3 main features. First it would take over the LCD display on the printer as a demonstration that they had full control of the device. Next it would check if the printer had an ethernet cable attached. If the cable is attached the third feature is activated – it attempts to attack and take control of other computers attached to the same network using previously leaked NSA tools Eternal Blue and Double Pulsar. While the demonstration exploit shown by the researchers changed the LCD on the printer, a real attacker’s exploit may instead opt to stay quiet to increase the time it goes undetected.
The fax machine attacked in their demonstration was an HP Officejet Pro 6830. HP was coordinated with after the vulnerabilities were discovered and patched firmware has been available on HP’s website since August 1st. While only one specific model was attacked in their demonstration it is possible that other models from other manufacturers may suffer from similar flaws due to the nature of parsing complex file formats from unknown origins.
The researchers coordinated with HP to rectify the vulnerability;  patched firmware has been available from HP since August 1st. This means special care should be taken similar to other riskier devices on the network, such as ensuring that the devices are firewalled off appropriately or on different network segments. While these precautions would prevent the device from being used as a door into the network, they wouldn’t protect against other types of local attacks. 

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