Today, we hope that even the cheapest recorder smartphones can be equipped with a multi-core processor, at least 1 GB of RAM, and a Linux-based operating system. But obviously, for older POTS desk phones, these specifications are unnecessary. Well, this is what we think. Then [Josh Max] Write to tell us about his adventures in cracking CaptionCall, And now we are eager to see what the community can do with root access on powerful Linux phones.
As the name suggests, CaptionCall is a desktop phone with an LCD above the keyboard that can display real-time subtitles. In the United States, anyone with hearing loss can get a mobile phone like this for free from the government, so naturally they will be sold at the price of peanuts on the second-hand market. Well, at least they did.Then [Josh] I had to continue to crack the root password of the ARMv7 i.MX6 mobile phone, start exploring around in its 4 GB onboard NAND, and let this thing run DOOM.
If you are interested in technical details, [Josh] Completed a great job, let us complete his process step by step. Anyone who has played with embedded Linux devices will at least be familiar with this story, unsurprisingly, starting with locating the serial port connector on the PCB.
Found that the environment variables were tightly locked, he took a slow route and used U-Boot’s “Memory Display” command to dump 80 characters of the phone’s firmware at a time.Pass the restored firmware image
binwalk A password cracker provided him with root credentials within a short period of time, and from there, the serial port became more useful.
[Josh] Kicked the original user interface of the phone to the side of the road, set up the ARM Debian Jessie chroot, and started working towards a fully functional Linux environment. After ensuring audio, video and even keyboard support, he is ready to launch everyone’s favorite shooting game of 1993. He kindly shared his work in the GitHub repository, Although this may not be a turnkey experience, all parts can be completely bent hardware according to your wishes.
Historically, running DOOM on new hardware heralds bigger and better things coming. With unrestricted access to its Linux operating system, we predict that CaptionCall will become a popular target for hacker attacks in the future, and we can’t wait to see it.