openssh2.2.p1 - Re: scp file transfer hole

[Martin MaD Douda <martin () DOUDA NET>]

Openssh2.2.0p1 IS vulnerable, but some change is needed in fake scp to
exploit it.

Using your scripts I could make suid scpuser's file in /tmp, but probably
due to some protocol change in scp, the file was empty and scp has died
with "lost connection".

Since openssh 2.2.0p1 is latest existing version, this vulnerability
probably exist in every single scp version in the world.


                                                Martin



On Sat, 30 Sep 2000, Michal Zalewski wrote:

> This issue appears quite often - tar suffers from problem of this kind as
> well (using cute symlink tricks, you can create an archive, which, when
> unpacked, can overwrite or create specific files anywhere in your
> filesystem). This time, similar scp vulnerability has been found and
> acknowledged in sshd 1.2.xx releases (no information on 2.0.xx).
>
> When you are scp'ing files from remote machine to your local computer,
> modified scp service on the second endpoint can spoof legitimate scp data,
> overwriting arbitrary files.
>
> As a proof of concept, I created trivial scp replacement (put it on remote
> machine in the place of original scp binary - usually in /usr/local/bin).
> It will try to exploit any file transfer, creating setuid /tmp/ScpIsBuggy
> file on client system:
>
> --
> #!/bin/bash
>
> echo "D0755 0 ../../../../../../tmp/nope"
> echo "D0755 0 ../../../../../../tmp"
> echo "C4755 200 ScpIsBuggy"
> dd if=/dev/urandom of=/dev/stdout bs=200 count=1 2>/dev/null
> dd if=/dev/zero of=/dev/stdout bs=1 count=2 2>/dev/null
> --
>
> This isn't really nice :P After SSH become popular, people started to
> transfer files using scp (both user files and backups, logs etc).
> Successful exploitation of single server (or even single account) might
> cause futher intrusions on client machines.
>
> Another thing I can imagine - automated scp worm, which will, after
> intrusion, intercept futher scp sessions (eg. using ptrace) to send itself
> to remote system (and, probably, doing other operations as well). This
> doesn't actually require it to operate on privledged level :>
>
> What's probably the most alarming, there is no simple way to detect such
> attack - path is stripped before displaying filenames on client side -
> in above example, you'll see successful transfer of ScpIsBuggy file,
> suggesting it has been downloaded in current directory. Also, file modes
> are not verified, so suid files can be placed in remote system (but that's
> not the point, even without it, remote attack eg. on .ssh/authorized_keys
> is possible).
>
> _______________________________________________________
> Michal Zalewski [lcamtuf () tpi pl] [tp.internet/security]
> [http://lcamtuf.na.export.pl] <=--=> bash$ :(){ :|:&};:
> =-----=> God is real, unless declared integer. <=-----=

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                              Martin "MaD" Douda
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[1]+  Done               rm -rf /