Re: A Strang bug using Ctrl-N, perhaps a way to deny service on a shell

[Frank de Lange <secf-frank () unternet org>]

On Sun, Dec 16, 2001 at 02:22:27AM -0500, Ben Allen wrote:
> (This is a post that I sent to BugTraq)
> I've found a bug. I'm not sure what the bug is in. Since it is so widely
> found I can't find out what it is.
> For an example telnet into any SMTP server you like from a unix prompt.
> I've only tested from OpenBSD 3.0 Current. Now enter this is:
> ^N^N^N
> <Return>
> ^N
> <Return>
> ^N

Those 'weird characters' are the result of your terminal switching to the
'alternate character set' (a.k.a. G1 character set) when it saw that ctrl-n
(also known as 'shift-in') passing by. This is a VT100 feature. To go back to
the normal (G0) character set, enter the following sequence:

  <ctrl-v><ctrl-o>
  <enter>

The ctrl-o is also known as 'shift out'.

Sometimes you also have to use:

  stty sane

This will reset the terminal to a 'sane' state. It will not, however, change
the character set. For that you need to enter the sequence mentioned above.

You can provoke the switch to the G1 character set by entering:

  <ctrl-v><vtrl-n>
  <enter>

//Frank
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