On 3 July 2017 at 01:22, Eli Schwartz via arch-general
<arch-general@xxxxxxxxxxxxx> wrote:
> On 07/02/2017 07:01 PM, Ismael Bouya wrote:
>> (Mon, Jul 03, 2017 at 12:29:44AM +0200) Morten Linderud :
>>> But HTTPS doesnt matter here. We have a trusted signer inn the PKGBUILD, anyone can MITM for the good of their life.
>>> Unless they can fake the signature (Hint; they cant), or trick Lennart into signing something he shouldnt (Hint; he
>>> wont), we don't have a case here. It doesn't really matter if its HTTP or HTTPS.
>>>
>>> You also didn't really reply about the threat model.
>>
>> If I understand correctly what Nicohood meant,
>> what could happen is that version X of systemd (or anything else) has a
>> well known vulnerability, fixed in X+1. X+1 is packaged, so anyone
>> up to date thinks "good I'm safe now". But since a man in the middle can
>> force to download version X (signed by the systemd maintainer so
>> considered "secure"), he can force you to download that version when you
>> create the package and you'll think you have the safe version while
>> having the unsafe one.
>
> Okay, this I am genuinely curious about.
>
> In what circumstances can I have:
> - the systemd repository cloned over the git:// protocol
> - an annotated tag for systemd v233 signed by Lennart Poettering.
> - an annotated tag for systemd v232 signed by Lennart Poettering.
> - a man in the middle attack
> - `git verify-tag --raw v233` reports a GOODSIG with a VALIDSIG
> ${fingerprint} that matches with Lennart's known GPG fingerprint as
> recorded in validpgpkeys
>
> And as a result, when I run the git command `git checkout
> refs/tags/v233`, I am tricked into getting v232 instead which contains a
> vulnerability. Also, I wouldn't be alerted by the verbose printing of
> the systemd version which happens during the boot process, nor by
> $systemd_binary --version
>
> ...
>
> Because I don't think git works that way, but I am willing to be proven
> wrong. Also I bet the git developers would be fascinated to hear the
> details, you might even get some sort of bounty for successfully hacking
> git like that.
On the other hand,
the systemd-stable repo doesn't have signed tags (or commits) and Arch
is probably going to move to that since it has post-release fixes for
regressions and bugs.
--
damjan
