Posts Tagged ‘utf16le’

So this is a quick post with hopefully the goal of saving somebody else some time. Just for the record, I could have missed something totally trivial and I will hopefully get corrected :)

When working with the registry_persistence module, it turns out that one of the registry entries turns into garbage. At first I blamed myself of course, but it turned out that this could probably be a bug in the meterpreter code of which I’m not sure if it really is a bug or if there is a new API call which I haven’t found yet. So when executing the module the registry looks like this:

registry_garbled

Like you can see that’s not exactly how it really should look like, since what we are expecting is something more human readable and an actual powershell command.

The quick work around is to generate the correct string with the correct encoding and for me it was easier to do this with python:

a = "%COMSPEC% /b /c start /b /min powershell -nop -w hidden -c \"sleep 1; iex([System.Text.Encoding]::Unicode.GetString([System.Convert]::FromBase64String((Get-Item 'HKCU:myregkey_name').GetValue('myregkey_value'))))\""
b = '\\x'.join("{:02x}".format(ord(c)) for c in a.encode('UTF-16LE'))
print '\\x' + b

You can then just hard code the output string into the module (replace the original ‘cmd=’ string with your hex encoded one like cmd=”\x25\x00″ etc) and it should appear correctly in your registry. Following screenshot shows before and after:

registry_fixed

If you are curious how you could debug similar bugs yourself, keep on reading for a short tour of the problem solving part. If you are wondering why I don’t submit a PR to metasploit, that’s cause unicode scares the **** out of me. My usual experience is I generate more problems when dealing with unicode than I intended to fix.

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