Re: How to reboot?

You bring an excellent point about the ability to spoof the email address. 
In my case the email that for the server is not made public, but that is a 
vulnerability. I will have to read up on pwgen. That sounds like a good 
authentication that changes like a token number.
Another approach could be secondary authentication where it sends something 
to my phone, and then waits for a text response from the phone before 
executing anything.
Tim
Get BlueMail <https://bluemail.me> for Desktop
hw wrote:
On Sat, 2024-01-13 at 08:49 -0600, twlewis via beginners wrote:
Hi hw, I had a similar situation in which I travelled. I wanted to
lock down the ufw firewall but be able to allow certain IP addresses
based on the hotel IP or my cell service IP. To that I developed
Perl that would check my smtp account. The script is controlled
through a cron job that runs as root. Through email I can send
commands to that email address that is set up for my server. I have
an INI file with parameters. The script reads that INI each time.
I control access to not allow any other outside email from sending
commands by using a specific email address in the INI that can send
commands.
How do you verify that the email was actually sent from the sender
address which is allowed to send commands?
The From: header is irrelevant, and I wouldn't trust Envelope-From:
headers either since that can also be faked. Using SPF and/or DKIM
might help, and you might have to go to some lengths to check on that.
I'd at least use a list of passwords, known only to your server and to
you, so every email you want processed needs to contain the next
password on the list to be considered. That's pretty simple to do,
and pwgen is your friend :)
Other than that, xmpp is way easier to process than emails, and
someone who wants to send something first needs to log into their
account with a password. That may be safer than just emails alone.
Another advantage is that emails can be delayed whereas xmpp is
(supposed to be) instant (and usually is).
Any other email addresses that attempt to send commands
are ignored and it sends me a report if this occurs.
When you use a UUID as the local part of the receiving address, it's
somewhat unlikely that anyone but you will send emails to it (unless
you publish the address).
In the Perl script I was able to set up things such as allowing
certain IPs in ufw, check disk space, run apt to update the server,
and even reboot the server.
I don't know if you have access to a SMTP email server or not.
I'm running one on my server which relays the emails through the SMTP
server of an email provider.
Creating this daemon is really only intended to allow me to
reboot/shutdown my workstation when the screen has gone black. That
sometimes happens since NVIDIA drivers aren't perfect. Of course, if
it gets otherwise locked up, the daemon will also be useful.
The other day I came back to my keyboard right when the display said
'no signal' because the screen saver had just switched it off, and I
pressed a button and the display remained switched off. Switching to
consoles and back didn't help, switching the display off and back on
didn't help either. I could't even get a picture on the 2nd monitor
(which is usually switched off but things go haywire when switching
displays on/off because someone programmed it stupidly so it does
unwanted stuff automatically despite the 2nd display is switched off,
and the 2nd display usually needs some convincing to work or doesn't
work at all when I try to enable it); pressing Ctrl+Atl+Del didn't do
anything, the Reset button of my workstation is probably disabled (I
need to check that in the BIOS) and at the point, the only thing
remains is to power it off while it's running, which I don't want to
do at all. All that is time consuming and annoying and that
Ctrl+Alt+Del doesn't work anymore is retarded, and I'm totally pissed
and I've had it.
So I created this daemon so I can least reboot my workstation when
things aren't working as they should. I could log in via ssl, but I'd
have to set up my laptop for that or the 2nd display and a keyboard
for the server which usually aren't connected, so that's also
annoying. It's not so difficult to send xmpp messages from a phone or
a tablet.
Gmail used to allow this type of interaction and allow log ins from
scripts, but I believe that they have locked down security to no
longer allow that.
You could use some dyndns provider like noip, and wireguard to connect
to your home network/server from afar. Wireguard is awesome, and
what's better than the option of having full access same as if you
were at home, or limited access if you want. It sure beats both xmpp
and emails.
Or you could directly connect to your xmpp server or email server
through wireguard to send commands, which would avoid doing it openly
over the internet.
I hope this helps.
Tim
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