An issue was discovered on Securifi Almond, Almond+, and Almond 2015 devices with…

Summary

An issue was discovered on Securifi Almond, Almond+, and Almond 2015 devices with firmware AL-R096. The device provides a user with the capability of setting name for wireless network. These values are stored by the device in NVRAM (Non-volatile RAM). It seems that the POST parameters passed in this request to set up names on the device do not have a string length check on them. This allows an attacker to send a large payload in the "mssid_1" POST parameter. The device also allows a user to view the name of the Wifi Network set by the user. While processing this request, the device calls a function named "getCfgToHTML" at address 0x004268A8 which retrieves the value set earlier by "mssid_1" parameter as SSID2 and this value then results in overflowing the stack set up for this function and allows an attacker to control $ra register value on the stack which allows an attacker to control the device by executing a payload of an attacker's choice. If the firmware version AL-R096 is dissected using binwalk tool, we obtain a cpio-root archive which contains the filesystem set up on the device that contains all the binaries. The binary "goahead" is the one that has the vulnerable function that recieves the values sent by the POST request. If we open this binary in IDA-pro we will notice that this follows a MIPS little endian format. The function sub_00420F38 in IDA pro is identified to be receiving the values sent in the POST parameter "mssid_1" at address 0x0042BA00 and then sets in the NVRAM at address 0x0042C314. The value is later retrieved in the function "getCfgToHTML" at address 0x00426924 and this results in overflowing the buffer due to "strcat" function that is utilized by this function.