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Date: Sat, 30 Mar 2024 09:22:09 +0100
From: Vegard Nossum <vegard.nossum@...cle.com>
To: oss-security@...ts.openwall.com, Ivan Delalande <colona@....fr>,
        Andres Freund <andres@...razel.de>,
        Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: backdoor in upstream xz/liblzma leading to ssh
 server compromise

On 29/03/2024 20:32, Vegard Nossum wrote:
> On 29/03/2024 19:54, Ivan Delalande wrote:
>> On Fri, Mar 29, 2024 at 08:51:26AM -0700, Andres Freund wrote:
>>> For which the exploit code was then adjusted:
>>> https://github.com/tukaani-project/xz/commit/6e636819e8f070330d835fce46289a3ff72a7b89
>>>
>>> Given the activity over several weeks, the committer is either directly
>>> involved or there was some quite severe compromise of their
>>> system. Unfortunately the latter looks like the less likely 
>>> explanation, given
>>> they communicated on various lists about the "fixes" mentioned above.
>> Knowing this, I hope the recent kernel patch series involving the same
>> person to some degree will get extra scrutiny:
>> https://lore.kernel.org/lkml/20240320183846.19475-1-lasse.collin@tukaani.org/t/
> 
> I *think* this patch series is safe and was just pushed to make more
> people upgrade to newer versions faster
I retract this.

A HackerNews comment/thread [1] points this out:

# Set XZ_VERSION (and LIBLZMA_VERSION). This is needed to disable features
# that aren't available in old XZ Utils versions.
eval "$($XZ --robot --version)" || exit

That is indeed scary -- exactly the kind of thing that sort of makes
sense in isolation (xz --robot --version outputs some environment
variables) and then just becomes a gadget for exploitation if xz were to
start outputting something different there.

[1] https://news.ycombinator.com/item?id=39869715


Vegard

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