Help sending multiple files using qrexec

[pr...@tutanota.de]

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Hi,

I am trying to send mutliple files using qrexec by catting the files using the
following scripts:

Script one on the client:

echo "$#"
while [ $1 ]; do
    echo $(wc -l $1)
    cat $1
    shift
done


Script two on the server:

read NUMFILES
READFILES=0
while [ $READFILES -lt $NUMFILES ]; do
    read CATFILESIZE CATFILENAME
    head -n $CATFILESIZE > "$CATFILENAME"
    ((READFILES++))
done


This successfully sends the first file, but not the second, can anyone help
with this or should I be using qvm-copy?

Thanks for reading
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[pixel fairy]

qvm-copy. 

if this done often between trusted qubes, you can pre approve the file copy in /etc/qubes-rpc/policy/qubes.Filecopy with a line like

srcvm destvm allow

[haaber]

> This successfully sends the first file, but not the second, can anyone help
> with this or should I be using qvm-copy?

I don't say what you should, or should not, but what I think is more
easy: recall that qvm-copy or qvm-move take certainly multiple files.
The question is more intriguing if the list of files is produced by a
find command, or a for loop in bash.
Then you don't want to click each time on the "target qube" window that
dom0 will present. In such a case, to avoid loosing time, I would simply
write the list of all files in a small file (no newlines, just blanks)
and then use qvm-copy command on that list once. Or you through
everything in a non-comressed tar file and push that one over. Not
elegant, but fast & easy.

[M]

Can a hacker use the same script to transfer files from a victims pc remotely ?

And if so, how easy is it ?

[pr...@tutanota.de]

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I should have mentioned that this was part of a bigger script, using qvm-copy
would have required me to also pass along the qube name, so I could then cd to
the correct QubesIncoming directory. Keeping it simple I went with tar:

Script one on the client:

tar -c $@ | cat

Script two on the server:

cat | tar -x

Thanks for the help!

> Can a hacker use the same script to transfer files from a victims pc remotely ?
> And if so, how easy is it ?

This can't be used remotely, the server I mention above is another virtual
machine in the same Qubes system. This is just sending files between two qubes
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[David Hobach]

On 12/5/19 3:28 AM, pr...@tutanota.de wrote:
>
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> Hash: SHA512
>
> I should have mentioned that this was part of a bigger script, using qvm-copy
> would have required me to also pass along the qube name, so I could then cd to
> the correct QubesIncoming directory. Keeping it simple I went with tar:
>
> Script one on the client:
>
> tar -c $@ | cat
>
> Script two on the server:
>
> cat | tar -x
>
> Thanks for the help!

It might also work without cat, tar just doesn't like to print to shells.

And you'll probably want to quote your $@ --> "$@" for files with spaces
and other special characters if you're running inside bash.

>> Can a hacker use the same script to transfer files from a victims pc remotely ?
>> And if so, how easy is it ?
> This can't be used remotely, the server I mention above is another virtual
> machine in the same Qubes system. This is just sending files between two qubes

If tar is exploitable, then the client VM can use that exploit on the
server VM above to execute code, yes. Also see [1].

For example the first script of this topic should be fairly easy to exploit.

In total I'd recommend to stick with the means provided unless
absolutely necessary.

[1] https://www.qubes-os.org/doc/qrexec/