PLEASE HELP - regarding setting up a CAPTIVE PORTAL with hostapd/dnsmasq on LINUX

1

Hello everyone,
I need your advice on setting up the detection and redirection of the captive portal page.
I feel really stuck right now because i don’ understand why its not working.
I would REALLY appreciate if you could help me!
This is my set up:

on fresh kali linux vm:
sudo apt update

Setting up hostapd:

sudo apt install dnsmasq hostapd
sudo nano /etc/hostapd/hostapd.conf

interface=wlan1

driver=nl80211
ssid=test
hw_mode=g
channel=1

Setting up static ip for ap:
sudo ip link set wlan1 down
sudo ip addr add 10.0.0.1/24 dev wlan1
sudo ip link set wlan1 up

Setting up dnsmasq (redirects all dns requests to webpage):
ctrl + k , delete all the inside text of dnsmasq
sudo nano /etc/dnsmasq.conf

Interface and DNS binding

interface=wlan1
listen-address=10.0.0.1
bind-interfaces

DHCP pool and options

dhcp-range=10.0.0.10,10.0.0.200,12h
dhcp-option=3,10.0.0.1 # default gateway
dhcp-option=6,10.0.0.1 # tell clients to use the AP for DNS

Redirect all DNS names to the AP IP (captive-portal / block)

address=/#/10.0.0.1

address=/captive.apple.com/10.0.0.1
address=/captive.apple.com./10.0.0.1
address=/captive.apple.com/hotspot-detect.html/10.0.0.1

address=/connectivitycheck.gstatic.com/10.0.0.1
address=/clients3.google.com/10.0.0.1
address=/clients4.google.com/10.0.0.1
address=/connectivitycheck.android.com/10.0.0.1

address=/www.msftconnecttest.com/10.0.0.1
address=/msftconnecttest.com/10.0.0.1
address=/msftncsi.com/10.0.0.1
address=/edge-http.microsoft.com/10.0.0.1

address=/detectportal.firefox.com/10.0.0.1
address=/detectportal.brave-http-only.com/10.0.0.1
address=/nmcheck.gnome.org/10.0.0.1
address=/networkcheck.kde.org/10.0.0.1

Optional: forward upstream instead of redirecting

no-resolv

server=10.0.0.1

server=8.8.8.8

Example static lease (fixed IP for a device)

dhcp-host=aa:bb:cc:dd:ee:ff,10.0.0.20

Restart service, it starts the dnsmasq:
sudo systemctl restart dnsmasq

Enable IPv4 forwarding:
sudo sysctl -w net.ipv4.ip_forward=1

nano /etc/resolv.con

nameserver 10.0.0.1

start hostapd - and wait 30 seconds, it should show up:
sudo hostapd -d /etc/hostapd/hostapd.conf

Setting up webpage:

  • new terminal
    sudo apt update
    sudo apt install nginx
    sudo nano /etc/nginx/sites-available/ap

server {
listen 10.0.0.1:80 default_server;
server_name _;
root /var/www/ap;
index index.html;

location /generate_204 {
    return 200 " ";  # Keep it minimal; a space is sufficient
}

location = /hotspot-detect.html {
    return 200 " ";  # Likewise, return a success response
}

location = /success.txt {
    return 200 "This is a captive portal";  # Or any other content
}

location / {
    try_files $uri $uri/ =404;  # Serve index.html for general requests
}

}

sudo mkdir -p /var/www/ap

sudo nano /var/www/ap/index.html

Hello from AP 10.0.0.1

--------------

sudo chown -R www-data:www-data /var/www/ap

check if the html code works and if you can start nginx:
sudo nginx -t

flush rules:
sudo iptables -F
sudo iptables -t nat -F
sudo iptables -X

reset to default:
sudo iptables -P INPUT ACCEPT
sudo iptables -P FORWARD ACCEPT
sudo iptables -P OUTPUT ACCEPT

allow port 80 on ap interface:
sudo iptables -A INPUT -i wlan1 -p udp --dport 53 -j ACCEPT
sudo iptables -A INPUT -i wlan1 -p tcp --dport 53 -j ACCEPT
sudo iptables -A INPUT -i wlan1 -p tcp
sudo iptables -t nat -A PREROUTING -i wlan1 -p tcp --dport 80 -j DNAT --to-destination 10.0.0.1
sudo iptables -A FORWARD -i wlan1 -p udp --dport 53 -j ACCEPT
sudo iptables -A FORWARD -i wlan1 -p tcp --dport 53 -j ACCEPT
sudo iptables -A FORWARD -i wlan1 -p tcp -d 10.0.0.1 --dport 80 -j ACCEPT
sudo iptables -t nat -A POSTROUTING -o wlan1 -j MASQUERADE

link:
sudo ln -s /etc/nginx/sites-available/ap /etc/nginx/sites-enabled/ap

sudo systemctl restart nginx

finally:
sudo aormon-ng check kill
sudo hostapd -d /etc/hostapd/hostapd.conf

to stop hosting:
ctrl + c

I can confirm this after testing:

  • you can connect to ap
  • you are connected without internet and wifi is open
  • the ap stays connected for 40 minutes to clients without problem (after this this, idc probably too)

On the phone (android):

  • when connecting you get asked if you want to continue connection without internet or disconnect
  • a browser isn’t opened with the AP page (the browser doesn’t open at all)
  • if you browse for google.com, amazon.com → it says connection refused
  • if you browse for 10.0.0.1 the AP page is shown
  • if you browse for newsell.com the AP page shows up
  • if you browse for 1.1.1.1, or 1.2.3.4 etc the AP page is shown

On Windows:

  • a browser isn’t opened with the AP page (the browser doesn’t open at all)
  • if you browse for google.com, amazon.com → it says it refused to connect
  • if you browse for 10.0.0.1 the AP page is shown
  • if you browse for newsell.com the AP page shows up
  • if you browse for 1.1.1.1, or 1.2.3.4 etc the AP page is shown

issues:

  • the browser doesn’t open automatically with the webpage on 10.0.0.1 after connecting to the ap

Note: I admit I relied a bit on the help of an AI but i do understand that code and how the systems: Windows, Iphone, Android, Mac have build in code with a specific url to check for captive portals when connecting to a new wifi.
Once again, please help, I would REALLY appreciate it!!!