[arch-general] Sébastien Luttringer and Tobias Powalowski

Morten Linderud morten at linderud.pw
Sun Jul 2 22:21:01 UTC 2017

On Mon, Jul 03, 2017 at 12:16:53AM +0200, NicoHood wrote:
> On 07/03/2017 12:07 AM, Morten Linderud wrote:
> > On Sun, Jul 02, 2017 at 11:55:35PM +0200, NicoHood wrote:
> >> Yes the GPG signature of the tag commit is checked. However you can
> >> attack the git metadata and set a tag to a different commit. If this
> >> commit is signed, but at an older stage which is vulnearable, we have an
> >> issue. Just one example. So we should always also secure the transport
> >> layer.
> >> https://www.usenix.org/conference/usenixsecurity16/technical-sessions/presentation/torres-arias
> >>
> > 
> > The sign includes the hash. You would essentially have to trick Lennart into replacing the tag to a different commit,
> > and sign the tag. Creating a vulnerable but verified source for the PKGBUILD. At this point i think we have bigger
> > problems then whatever the PKGBUILD is doing...
> > 
> Thats is exactly what I mean. If I understood right you can modify the
> git metadata in a way that you can pull tag 1.2 but get 1.0. And tag 1.0
> is gpg signed and all valid. This seems to work for me.

But at this point you can't trust critical maintainers of important software. This isn't a threat model i think
PKGBUILDs (or Arch for that matter) really cares about. Am i wrong? Or are you implying MITM attacks can trick the
packager into packaging broken software?

Morten Linderud

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