A newly attached public IP quietly puts a resource on the internet

Why it happens

Attaching a public IP is a single property change — the IP's ipConfiguration starts pointing at a NIC or front-end config — and Azure treats it as ordinary networking, not a security event. There's no separate "you are now internet-facing" confirmation step.

It happens through the most routine actions: ticking "Public IP" while creating a VM, adding a front end to a load balancer, or a template redeploy that reintroduces an association someone had deliberately removed. Whether the newly exposed endpoint is actually protected then depends entirely on the NSG and firewall rules behind it, which are configured separately and easy to get wrong. The attachment lands quietly and the resource is live on the internet before anyone reviews what's listening.

What it costs / blast radius

The public IP itself is a few dollars a month, but that isn't the point. The blast radius is new internet exposure: any port the resource listens on is now reachable from anywhere unless an NSG or firewall explicitly blocks it. (Azure behavior; authored assessment.) A management port, a database engine, or an admin panel that was safely private a moment ago becomes a target the instant the association is made, and the change leaves no obvious trail unless someone is watching for it.

See it

resource nic 'Microsoft.Network/networkInterfaces@2023-09-01' = {
  name: 'app-vm-nic'
  location: location
  properties: {
    ipConfigurations: [ {
      name: 'ipconfig1'
      properties: {
        subnet: { id: subnet.id }
        privateIPAllocationMethod: 'Dynamic'
        publicIPAddress: { id: publicIp.id }   // now reachable from the internet
      }
    } ]
  }
}

resource nic 'Microsoft.Network/networkInterfaces@2023-09-01' = {
  name: 'app-vm-nic'
  location: location
  properties: {
    ipConfigurations: [ {
      name: 'ipconfig1'
      properties: {
        subnet: { id: subnet.id }
        privateIPAllocationMethod: 'Dynamic'
        // no publicIPAddress -> private only; reach it via Bastion / a
        // load balancer whose NSG restricts inbound to known sources
      }
    } ]
  }
}