From: Joann Mõndresku <joann@cernodile.com>
Date: Sat, 20 Aug 2022 12:04:20 +0000 (+0300)
Subject: SSH Alerts Landchad style.
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SSH Alerts Landchad style.
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diff --git a/articles/ssh-alerts-landchad-style.md b/articles/ssh-alerts-landchad-style.md
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+How to setup SSH alerts like a landchad
+
+# Preface
+I recently installed ntfy to enable UnifiedPush on several apps on my phone
+in order to conserve battery life and make notifications work more real-time.
+That gave me the idea that I can use this same idea for creating SSH intrusion
+alerts for my server for that extra peace of mind.
+
+## Installing ntfy
+Installing it is quite straightforward. You can find [guide for installing it on their website.](https://ntfy.sh/docs/install/)
+In my instance, I had to install it for Ubuntu, so following commands had to
+be executed:
+
+```
+curl -sSL https://archive.heckel.io/apt/pubkey.txt | sudo apt-key add -
+sudo apt install apt-transport-https
+sudo sh -c "echo 'deb [arch=amd64] https://archive.heckel.io/apt debian main' \
+    > /etc/apt/sources.list.d/archive.heckel.io.list"  
+sudo apt update
+sudo apt install ntfy
+sudo systemctl enable ntfy
+sudo systemctl start ntfy
+```
+
+Now this enables anonymous access and everything to your server. That is cool
+and all if you wish to offer this for public, but it comes with its own
+reprecussions. I wished to keep my instance private just to eliminate interference
+with my own alerts and also have more trust in the system.
+You do not want to deal with phishers using YOUR instance or bad actors to
+derail you with false alerts.
+
+In order to privatize your instance, you need to open /etc/ntfy/server.yml and
+edit the following:
+
+```
+auth-file: "/var/lib/ntfy/user.db"
+auth-default-access: "deny-all"
+```
+
+This leaves you with a bare setup and may not fully suit your previously installed
+services. In my case I had to create a reverse-proxy for it.
+You can find the template for your preferred webserver in their docs. One thing
+to keep in mind though with their nginx template, is that you will need to add
+IPv6 listener manually should you use IPv6 on your server as it's absent.
+Generate an SSL certificate using certbot and nginx plugin.
+
+Edit your configuration again as follows:
+
+```
+base-url: https://<your based domain or subdomain>
+listen-http: "127.0.0.1:2586" # can be your preferred port too.
+behind-proxy: true # only if reverse-proxy. otherwise false, listen-http to 0.0.0.0 and provide ssl certs as well in config.
+
+# optionally enable cache incase your push notif receivers go offline for prolonged time.
+cache-file: /var/cache/ntfy/cache.db
+cache-duration: "12h"
+```
+
+If you are also using Debian or Ubuntu, run `systemctl restart ntfy`. You should
+now have a private instance of ntfy provided your reverse proxy worked out.
+Next up you should create an admin account for your administrative needs with
+`ntfy user add --role admin <youradminuser>`. Use this when necessary.
+You should also create your own user with `ntfy user add <user>`.
+
+In order to make your instance UnifiedPush compatible, you need to give world
+access to write to service URLs with `ntfy access everyone 'up*' write-only`.
+Now you can give permissions for yourself as well - you can be generous here and
+give read-write to everything with `ntfy access <user> '*' read-write`.
+
+By now everything should be functioning as intended and your instance is compatible
+with UnifiedPush and you can start receiving notifications through it.
+
+Install the ntfy mobile app from F-Droid or your preferred application library.
+Go to settings of the app, add user pointing to your instance with credentials
+of your previously created user.
+
+## Creating the monitor
+Subscribe with your device to a new topic on your instance, I used "sysalerts"
+myself.
+
+Next up, create a new monitor user on your server: `ntfy user add monitor`.
+Give it permission to your ssh alerts topic. `ntfy access monitor 'sysalerts' write-only`.
+
+Create a script file in world-accessible path called "ssh_login.sh".
+Paste the following and modify according to your setup:
+
+```
+#!/bin/bash
+MONITOR="monitor:password"
+CURTIME=$(date)
+INSTANCE="your.based.server"
+TOPIC="sysalerts"
+
+if [ "$PAM_TYPE" != "close_session" ]; then
+	if [ "$PAM_USER" == "git" ]; then
+		exit 0
+	fi
+	ntfy publish \
+	-u "$MONITOR" \
+	--tags warning \
+	--title "Successful SSH authentication" \
+	"$INSTANCE/$TOPIC" \
+	"There has been a successful login to ssh on cernodile.com.
+User $PAM_USER from IP $PAM_RHOST on $CURTIME"
+fi
+```
+
+Make it world-executable `chmod ugo+x ssh_login.sh` and edit `/etc/pam.d/sshd`.
+
+Append the following line to it: `session optional pam_exec.so seteuid /path/to/ssh_login.sh`.
+
+This will make the script be run every single time someone authenticates through SSH and also not block login if
+the script is not absent.
+
+Just to be sure, keep your current SSH session and alive and try opening a second one. If everything is done
+correctly, you should have a notification on your phone (or desktop if you subscribed on it as well).
+
+## Closing words
+I understand this may not be a fully elegant solution and there can be security implications here.
+I am open to improving this solution, a healthy dialogue is encouraged on the topic. So far this has been
+working without an issue. You can easily set it up with a public provider too (nfty themselves have a public 
+instance!), but that would defeat the purpose of being a landchad.
+
+[The alert looks something like this (img size 33K)](/img/ssh-ntfy.png)
+
+
+Thanks for reading,
+- Cernodile
+
+;tags:privacy linux opensource tutorial
+;description:Have you thought of creating a SSH intrusion alert system, but don't want to integrate a full on monitoring-stack such as Nagios? In this blog, I walk you through on installing ntfy, making it a UnifiedPush provider and a useful tool for monitoring your SSH logins.
+;og_image:<meta property="og:image" content="https://based.quest/img/ssh-ntfy.jpg">
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