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Date: Sat, 30 Mar 2024 16:10:04 +0100
From: "Rein Fernhout (Levitating)" <me@...itati.ng>
To: oss-security@...ts.openwall.com
Cc: Jonathan Schleifer <js@....im>
Subject: Re: Re: backdoor in upstream xz/liblzma leading to ssh
server compromise
The script attached by Andres was from 5.6.0.
I extracted the script from both versions and I can verify your diff.
I attached the two versions I extracted.
It definitely does look like the 5.6.1 version looks for 2 extra scripts
to execute.
I don't get any matches on the greps either though.
For reference these are all the test files uploaded by Jia Tan, with
commit hash and summary:
bad-3-corrupt_lzma2.xz 74b138d2a6529f2c07729d7c77b1725a8e8b16f1
Tests: Update two test files.
bad-dict_size.lzma cf44e4b7f5dfdbf8c78aef377c10f71e274f63c0
Tests: Add a few test files.
good-1-riscv-lzma2-1.xz a67dcce6109c2f932a0a86abb0d7a95d3c31fb3e
Tests: Update RISC-V test files.
good-1-riscv-lzma2-2.xz a67dcce6109c2f932a0a86abb0d7a95d3c31fb3e
Tests: Update RISC-V test files.
good-2cat.xz cf44e4b7f5dfdbf8c78aef377c10f71e274f63c0
Tests: Add a few test files.
good-large_compressed.lzma 74b138d2a6529f2c07729d7c77b1725a8e8b16f1
Tests: Update two test files.
good-small_compressed.lzma cf44e4b7f5dfdbf8c78aef377c10f71e274f63c0
Tests: Add a few test files.
I also want to look more into the object file.
On 2024-03-30 13:14, Jonathan Schleifer wrote:
> (Sorry, I'm not subscribed to the list, and it seems the web interface
> doesn't expose the message ID so that I could add the appropriate
> headers, so this will probably not show up us as proper reply.)
>
> After reading this, I took a look at xz-5.6.1.tar.bz2 and extracted the
> payload manually myself. The `sed \”r\n\” $gl_am_configmake` never
> worked for me, so instead I replaced that with cat and could still get
> the script extracted.
>
> However, the script I extracted has a diff: http://sprunge.us/okPUXN
>
> This seems to look for yet another test and if it exists extracts a
> shell script from yet another test - before even checking any of the
> abort conditions. I think the assumption "If you don't build an RPM /
> deb, you're fine" probably does not hold as a result.
>
> If I run those greps manually, I have no matches. So this could mean
> this is just future proofing for future tests to be checked in.
> However, I suspect that this is because I extracted the script without
> executing configure, so I'm guessing there is a transformation missing
> that would transform these greps to something else that would then
> match.
>
> Has anyone else looked into this in more detail? My impression is that
> everybody went by the initial analysis, assumed they are safe and
> didn't do any further reversing.
>
> Also I've looked at the .o that gets linked in. It's 88 KB in size and
> uses misleading symbols: They are symbols that actually exist in
> liblzma, but prefixed with .L, meaning they are local - and do
> something else entirely than the name implies. I did some static
> analysis, but then hit an indirect branch where I don't know where it
> goes. In any case, 88 KB is a lot for just a backdoor in SSH, so I'm
> wondering if it does more.
>
> I think there really needs to be more reverse engineering. Is there any
> such effort? I think it would make sense to join forces and start a
> group.
View attachment "injected-61.txt" of type "text/plain" (9571 bytes)
View attachment "injected-60.txt" of type "text/plain" (8236 bytes)
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