Reproduction Steps:
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1. Access the wifi router gateway [i.e, http://192.168.1.254]
2. Go to "Wireless Setting" -> "Basic"
3. Update "Network Name(SSID)" field with '<script>alert("S@Y@N")</script>'
4. Save the settings.
5. Go to "System Status" and you will be having "S@Y@N" popup.