As a complimentary answer, in terms of Intel, nobody really knows because, for one, thus far no one has been able to figure out the custom compression algorithm that's used for packing portions of the underlying on-die and on-board binaries used to drive this feature.
Compound that with the fact that attempts to dump shared libraries for the code, including some elusive binary that implements core functions such as
memcpy and such yields nothing when you try, and we're all completely blind and in the dark. It's there, but not when you to try to get at it.
Here are some quotes from this article:
With a trusted processor connected directly to the memory, network,
and BIOS of a computer, the ME could be like a rootkit on steroids in
the wrong hands. Thus, an exploit for the ME is what all the
balaclava-wearing hackers want, but so far it seems that they’ve all
come up empty.
With regards to who's working on it, and problems faced:
The best efforts that we know of again come from [Igor Skochinsky].
After finding a few confidential Intel documents a company left on an
FTP server, he was able to take a look at some of the code for the ME
that isn’t in the on-chip ROM and isn’t compressed by an unknown
algorithm. It uses the JEFF file format, a standard from the defunct J
Consortium that is basically un-Googlable. (You can blame Jeff for
that.) To break the Management Engine, though, this code will have to
be reverse engineered, and figuring out the custom compression scheme
that’s used in the firmware remains an unsolved problem.
Another quote that points out the fact that since we cannot see the code, we have true idea of just how bad this could be:
There are many researchers trying to unlock the secrets of Intel’s
Management Engine, and for good reason: it’s a microcontroller that
has direct access to everything in a computer. Every computer with an
Intel chip made in the last few years has one, and if you’re looking
for the perfect vector for an attack, you won’t find anything better
than the ME. It is the scariest thing in your computer, and this fear
is compounded by our ignorance: no one knows what the ME can actually
do. And without being able to audit the code running on the ME, no one
knows exactly what will happen when it is broken open.
There are websites set up for people who want to work on the problem of figuring out the unknown compression algorithm. One such example is http://io.netgarage.org/me/.
Your best bet for finding tools that enable you to start getting your hands on at least portions of the firmware will be to Google "Igor Skochinsky". You can view his Github account to find what he has published.
All that said, I'm going to try and find my old dual pentium III system and go back to the stone age I guess. :)
The GNU LibreBoot project also has an extensive write up about the Intel ME as well here. It's worth a read. Here's a snippet that sums up their views:
The Intel Management Engine with its proprietary firmware has complete
access to and control over the PC: it can power on or shut down the
PC, read all open files, examine all running applications, track all
keys pressed and mouse movements, and even capture or display images
on the screen. And it has a network interface that is demonstrably
insecure, which can allow an attacker on the network to inject
rootkits that completely compromise the PC and can report to the
attacker all activities performed on the PC. It is a threat to
freedom, security, and privacy that can't be ignored.
For completeness, the LibreBoot project also has a write up about AMD Platform Security Processor, the AMD branded
back-door version of Intel's ME. You can find that here. Again, a quote summarizing their opinions on the matter:
In theory any malicious entity with access to the AMD signing key
would be able to install persistent malware that could not be
eradicated without an external flasher and a known good PSP image.
Furthermore, multiple security vulnerabilities have been demonstrated
in AMD firmware in the past, and there is every reason to assume one
or more zero day vulnerabilities are lurking in the PSP firmware.
Given the extreme privilege level (ring -2 or ring -3) of the PSP,
said vulnerabilities would have the ability to remotely monitor and
control any PSP enabled machine. completely outside of the user's