Linux login method secure?
richard at nezumi.plus.com
Sun Sep 1 23:28:58 PDT 2002
* T.B. van der Molen <tbm at home.nl> [2002-09-02 06:54]:
> I was wondering the following.
> On Windows NT/2000/whatever you usually first have to press Ctrl+Alt+Del
> before you can log on. This way you are sure you are giving your login
> information to Windows because only Windows can recognize the
> Ctrl+Alt+Del key combination.
> This does not exist in the Linux login method. So, someone could easily
> write a program or script that visually imitates the behaviour of the
> login program on a system, capture the user's login information and
> could then exit and log out so the user sees the real login program.
> Isn't this a relevant security threat? Can it be prevented?
This is a security flaw.
It can be prevented.
When compiling the kernel, add:
Kernel hacking --->
[*] Kernel debugging
[*] Magic SysRq key (NEW)
Pessing <alt><sysrq>k (the Secure Access Key) will kill any processes
on the current terminal. Init should then start *getty, so you can
be confident that you are not giving your password to a script.
The bad news is, this enables some debugging features like
<alt><sysrq>b - reboot the system without unmounting anything. This
is not such a disaster for most systems. A malicous person could always
pull the power cord. According to the documentation, you can use the
magic sysrq key on keyboard attached to a standard PC serial port.
If you lock crackers out of the room with the PC, but give them acces
to the serial port, then you should think carefully before enabling
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