oss-security - Re: backdoor in upstream xz/liblzma leading to ssh server compromise

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Date: Wed, 17 Apr 2024 16:38:54 +0200
From: Jakub Wilk <jwilk@...lk.net>
To: <oss-security@...ts.openwall.com>
Subject: Re: backdoor in upstream xz/liblzma leading to ssh
 server compromise

* Andres Freund <andres@...razel.de>, 2024-03-29 08:51:
>d) LANG needs to be set

If timing "sshd -h" is a reliable method of checking if the backdoor is 
active, then this is not correct. It seems all you need is non-empty 
environment:

    # time env -i /usr/sbin/sshd -h 2>/dev/null

    real    0m0.009s
    user    0m0.004s
    sys     0m0.005s

    # time env -i X= /usr/sbin/sshd -h 2>/dev/null

    real    0m0.345s
    user    0m0.337s
    sys     0m0.009s

Further evidence that LANG doesn't matter:
* LANG is not on the list of extracted strings[0].
* Some folks[1][2] misspelled LANG as LC_LANG, and apparently it still 
worked.

[0] https://gist.github.com/q3k/af3d93b6a1f399de28fe194add452d01
[1] https://gist.github.com/smx-smx/a6112d54777845d389bd7126d6e9f504
[2] https://github.com/binarly-io/binary-risk-intelligence/tree/master/xz-backdoor

>I am *not* a security researcher, nor a reverse engineer.

Congrats, you've just made a lot of people feel inadequate. :P

-- 
Jakub Wilk

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