[Cryptography] SHA1 collisions make Git vulnerable to attakcs by third-parties, not just repo maintainers

[Jason Cooper]

One final note:

On Fri, Feb 24, 2017 at 02:56:28AM +0000, Jason Cooper wrote:
...
> Just to be clear, this is now a *real* problem.  How long it takes from
> spotting an object of interest to creating a replacement object is the
> critical variable here.  The longer it takes to create, the more
> time people have to get a legit copy of the object before the malicious
> one can be injected.  Large projects with a plethora of objects (Linux
> Kernel) need to start the timer now.  Although, that's tempered by the
> fact that the juiciest targets are the new objects that no one has.

After reading through the git ml thread that Ted already pointed to, the
key piece I was missing last night is that this isn't a chosen-image
attack.  e.g. you can't take $valid_commit, modify it, insert/append
some mutate-able garbage, and get $bad_commit where

  sha1($valid_commit) == sha1($bad_commit)

is true.  Well, not yet.  Not with this new attack.  But it's much
closer.  I'm glad the object_id conversion is already underway. :-)

> /me grumbles because majordomo is ignoring my git ml subscribe
> requests[1]

EBKAC.

thx,

Jason.