[syslinux] problem with PXElinux and security of local LAN
Jason Keltz
jas at cs.yorku.ca
Mon Dec 19 10:43:57 PST 2005
That solution sounds interesting albeit a bit complex for me to
implement. I'm not sure that I quite understand 3. If the comboot
code asks for a DHCP value, and that value is sent across the wire
encrypted, that seems to require adjusting that code on the DHCP
configuration on a regular basis as well... further, I also wonder if
it would be possible for a machine to insert itself between step 3 and
4... but definately food for thought.
Jason.
Murali Krishnan Ganapathy wrote:
> Here is an ideal solution. I dont know how much of this is really possible.
>
> (1) Set your BIOS to boot from the local hard disk.
> (2) Use SYSLINUX as your boot loader and run a COMBOOT code (stored in
> your hard disk)
> (3) The COMBOOT Code figures out Who the DHCP server it is talking to,
> and has some kind of check.
> (4) If check works out, then chain boot your PXE ROM
>
> First this is essentially security by obscurity, i.e. in step (3), I am
> assuming that the DHCP server sends an additional string X
> (actually COMBOOT code asks the DHCP server for X). There is some magic
> string hard wired into the COMBOOT code,
> which gets encrypted using the current date as the key. If the encrypted
> string is X then you can trust the DHCP server.
> If the bad guy finds out the magic string (which is never sent over the
> network), then there is no security left.
>
> It would be cool if this can be implemented. One real life situation
> where SYSLINUX on HDD beats other boot loaders.
>
> - Murali
>
> Jason Keltz wrote:
>
>> Hi.
>>
>> I want to use PXELinux to build a dynamic boot menu for a computer
>> lab. Sometimes, the machines need to be in Linux mode/Windows
>> mode/allow the option of Linux/Windows. I configured this all fine
>> with PXELinux. My problem is really one of security. Someone can
>> plug in a laptop with a DHCP server, and tftp server and fake a lab
>> machine to boot into any mode they desire, or even worse, they could
>> configure the local machine to boot Linux in single user mode, and
>> hence allow access to root, local ssh keys, etc. I can't really think
>> of any easy way how to solve this problem since there is no way to
>> authenticate the PXELinux instance that is loading or the
>> configuration files. Any ideas? A locally configured grub could do
>> the same thing, of course, but using pxelinux, I can change the
>> configuration of machines that are off so that when they come back on,
>> they are in the mode that I desire.
>>
>> :(
>>
>> Jason.
>>
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>
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