[Cryptography] MITM watch - Tor exit nodes patching binaries
ianG
iang at iang.org
Wed Dec 3 09:39:32 EST 2014
The real MITMs are so rare that protocols that are designed around them
fall to the Bayesian impossibility syndrome (*). In short, false
negatives cause the system to be ignored, and when the real negative
indicator turns up it is treated as a false. Ignored. Fail.
Here's some evidence of that with Tor:
http://www.leviathansecurity.com/blog/the-case-of-the-modified-binaries/
... I tested BDFProxy against a number of binaries and update processes,
including Microsoft Windows Automatic updates. The good news is that if
an entity is actively patching Windows PE files for Windows Update, the
update verification process detects it, and you will receive error code
0×80200053.
.... If you Google the error code, the official Microsoft response is
troublesome.
If you follow the three steps from the official MS answer, two of those
steps result in downloading and executing a MS ‘Fixit’ solution
executable. ... If an adversary is currently patching binaries as you
download them, these ‘Fixit’ executables will also be patched. Since the
user, not the automatic update process, is initiating these downloads,
these files are not automatically verified before execution as with
Windows Update. In addition, these files need administrative privileges
to execute, and they will execute the payload that was patched into the
binary during download with those elevated privileges.
iang
(*) I'd love to hear a better name than Bayesian impossibility syndrome,
which I just made up. It's pretty important, it explains why the
current SSL/PKI/CA MITM protection can never work, relying on Bayesian
statistics to explain why infrequent real attacks cannot be defended
against when overshadowed by frequent false negatives.
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