Improper Neutralization of Special Elements used in a Command ('Command Injection')

Summary

An issue was discovered on D-Link DCS-1130 devices. The device provides a user with the capability of setting a SMB folder for the video clippings recorded by the device. It seems that the POST parameters passed in this request (to test if email credentials and hostname sent to the device work properly) result in being passed as commands to a "system" API in the function and thus result in command injection on the device. If the firmware version is dissected using binwalk tool, we obtain a cramfs-root archive which contains the filesystem set up on the device that contains all the binaries. The library "libmailutils.so" is the one that has the vulnerable function "sub_1FC4" that receives the values sent by the POST request. If we open this binary in IDA-pro we will notice that this follows an ARM little endian format. The function sub_1FC4 in IDA pro is identified to be receiving the values sent in the POST request and the value set in POST parameter "receiver1" is extracted in function "sub_15AC" which is then passed to the vulnerable system API call. The vulnerable library function is accessed in "cgibox" binary at address 0x00023BCC which calls the "Send_mail" function in "libmailutils.so" binary as shown below which results in the vulnerable POST parameter being passed to the library which results in the command injection issue.