On Amcrest IPM-721S V2.420.AC00.16.R.20160909 devices, the users on the device are divided into 2 groups "admin" and "user". However, as a part of security analysis it was identified that a low privileged user who belongs to the "user" group and who has access to login in to the web administrative interface of the device can add a new administrative user to the interface using HTTP APIs provided by the device and perform all the actions as an administrative user by using that account. If the firmware version V2.420.AC00.16.R 9/9/2016 is dissected using binwalk tool, one obtains a _user-x.squashfs.img.extracted archive which contains the filesystem set up on the device that many of the binaries in the /usr folder.

The binary "sonia" is the one that has the vulnerable functions that performs the various action described in HTTP APIs. If one opens this binary in IDA-pro one will notice that this follows a ARM little endian format. The function at address 0x00429084 in IDA pro is the one that processes the HTTP API request for "addUser" action.

If one traces the calls to this function, it can be clearly seen that the function sub_ 41F38C at address 0x0041F588 parses the call received from the browser and passes it to the "addUser" function without any authorization check.