diff --git a/src/main/kotlin/mdnet/base/Constants.kt b/src/main/kotlin/mdnet/base/Constants.kt
index 53293fe..4160745 100644
--- a/src/main/kotlin/mdnet/base/Constants.kt
+++ b/src/main/kotlin/mdnet/base/Constants.kt
@@ -26,4 +26,78 @@ object Constants {
 
     const val MAX_READ_TIME_SECONDS = 300
     const val MAX_WRITE_TIME_SECONDS = 60
+
+    // General list of ports to which Firefox and Chromium will not send HTTP requests for security reasons
+    // See:
+    //     * https://chromium.googlesource.com/chromium/src.git/+/refs/heads/master/net/base/port_util.cc
+    //     * https://developer.mozilla.org/en-US/docs/Mozilla/Mozilla_Port_Blocking#Blocked_Ports
+    @JvmField val RESTRICTED_PORTS = intArrayOf(
+        1, // tcpmux
+        7, // echo
+        9, // discard
+        11, // systat
+        13, // daytime
+        15, // netstat
+        17, // qotd
+        19, // chargen
+        20, // ftp data
+        21, // ftp access
+        22, // ssh
+        23, // telnet
+        25, // smtp
+        37, // time
+        42, // name
+        43, // nicname
+        53, // domain
+        77, // priv-rjs
+        79, // finger
+        87, // ttylink
+        95, // supdup
+        101, // hostriame
+        102, // iso-tsap
+        103, // gppitnp
+        104, // acr-nema
+        109, // pop2
+        110, // pop3
+        111, // sunrpc
+        113, // auth
+        115, // sftp
+        117, // uucp-path
+        119, // nntp
+        123, // NTP
+        135, // loc-srv /epmap
+        139, // netbios
+        143, // imap2
+        179, // BGP
+        389, // ldap
+        427, // SLP (Also used by Apple Filing Protocol)
+        465, // smtp+ssl
+        512, // print / exec
+        513, // login
+        514, // shell
+        515, // printer
+        526, // tempo
+        530, // courier
+        531, // chat
+        532, // netnews
+        540, // uucp
+        548, // AFP (Apple Filing Protocol)
+        556, // remotefs
+        563, // nntp+ssl
+        587, // smtp (rfc6409)
+        601, // syslog-conn (rfc3195)
+        636, // ldap+ssl
+        993, // ldap+ssl
+        995, // pop3+ssl
+        2049, // nfs
+        3659, // apple-sasl / PasswordServer
+        4045, // lockd
+        6000, // X11
+        6665, // Alternate IRC [Apple addition]
+        6666, // Alternate IRC [Apple addition]
+        6667, // Standard IRC [Apple addition]
+        6668, // Alternate IRC [Apple addition]
+        6669, // Alternate IRC [Apple addition]
+        6697 // IRC + TLS
+    )
 }
diff --git a/src/main/kotlin/mdnet/base/Main.kt b/src/main/kotlin/mdnet/base/Main.kt
index 9c1af90..1879682 100644
--- a/src/main/kotlin/mdnet/base/Main.kt
+++ b/src/main/kotlin/mdnet/base/Main.kt
@@ -109,6 +109,9 @@ object Main {
         if (settings.clientPort == 0) {
             dieWithError("Config Error: Invalid port number")
         }
+        if (settings.clientPort in Constants.RESTRICTED_PORTS) {
+            dieWithError("Config Error: Unsafe port number")
+        }
         if (settings.maxCacheSizeInMebibytes < 1024) {
             dieWithError("Config Error: Invalid max cache size, must be >= 1024 MiB (1GiB)")
         }