ikev2-setup.sh

#!/bin/bash -e

# github.com/jawj/IKEv2-setup
# Copyright (c) 2015 – 2020 George MacKerron
# Released under the MIT licence: http://opensource.org/licenses/mit-license

function exit_badly {
  echo "$1"
  exit 1
}

[[ $(lsb_release -rs) == "18.04" ]] || [[ $(lsb_release -rs) == "24.04" ]] || exit_badly "This script is for Ubuntu 20.04 or 18.04 only: aborting (if you know what you're doing, try deleting this check)"
[[ $(id -u) -eq 0 ]] || exit_badly "Please re-run as root (e.g. sudo ./path/to/this/script)"

echo "--- Adding repositories and installing utilities ---"
echo

export DEBIAN_FRONTEND=noninteractive

# see https://github.com/jawj/IKEv2-setup/issues/66 and https://bugs.launchpad.net/subiquity/+bug/1783129
# note: software-properties-common is required for add-apt-repository
apt-get -o Acquire::ForceIPv4=true update
apt-get -o Acquire::ForceIPv4=true install -y software-properties-common
add-apt-repository universe -y
add-apt-repository restricted -y
add-apt-repository multiverse -y

apt-get -o Acquire::ForceIPv4=true install -y moreutils dnsutils

echo
echo "--- Configuration: VPN settings ---"
echo

SSHPORT=${SSHPORT:-"22"}

if [[ -z "${VPNHOST}" ]]; then
    echo "VPNHOST evnironment variable is missing" >&2
    exit 0  
fi

if [[ -z "${VPNUSERNAME}" ]]; then
    echo "VPNUSERNAME evnironment variable is missing" >&2
    exit 0  
fi

if [[ -z "${EMAILADDR}" ]]; then
    echo "EMAILADDR evnironment variable is missing" >&2
    exit 0  
fi

VPNPASSWORD=$(< /dev/urandom tr -dc _A-Z-a-z-0-9 | head -c32)

ETH0ORSIMILAR=$(ip route get 1.1.1.1 | awk -- '{printf $5}')
IP=$(dig -4 +short myip.opendns.com @resolver1.opendns.com)

echo "Network interface: ${ETH0ORSIMILAR}"
echo "External IP: ${IP}"
echo
echo "** Note: this hostname must already resolve to this machine, to enable Let's Encrypt certificate setup **"

VPNHOSTIP=$(dig -4 +short "${VPNHOST}")
[[ -n "$VPNHOSTIP" ]] || exit_badly "Cannot resolve VPN hostname: aborting"

if [[ "${IP}" != "${VPNHOSTIP}" ]]; then
  echo "Warning: ${VPNHOST} resolves to ${VPNHOSTIP}, not ${IP}"
  echo "Either you're behind NAT, or something is wrong (e.g. hostname points to wrong IP, CloudFlare proxying shenanigans, ...)"
  exit_badly
fi

VPNDNS=${VPNDNS:-$(resolvectl | grep "Current DNS Server" | awk '{print $4}')}

echo
echo "--- Configuration: general server settings ---"
echo

LOGINUSERNAME=$(whoami)
VPNIPPOOL="10.101.0.0/16"

echo
echo "--- Upgrading and installing packages ---"
echo

apt-get -o Acquire::ForceIPv4=true --with-new-pkgs upgrade -y
apt autoremove -y

debconf-set-selections <<< "postfix postfix/mailname string ${VPNHOST}"
debconf-set-selections <<< "postfix postfix/main_mailer_type string 'Internet Site'"

apt-get -o Acquire::ForceIPv4=true install -y \
  language-pack-en iptables-persistent postfix mutt unattended-upgrades certbot uuid-runtime \
  strongswan libstrongswan-standard-plugins strongswan-libcharon libcharon-extra-plugins

# in 22.04 libcharon-standard-plugins is replaced with libcharon-extauth-plugins
apt-get -o Acquire::ForceIPv4=true install -y libcharon-standard-plugins \
  || apt-get -o Acquire::ForceIPv4=true install -y libcharon-extauth-plugins

echo
echo "--- Configuring firewall ---"
echo

# firewall
# https://www.strongswan.org/docs/LinuxKongress2009-strongswan.pdf
# https://wiki.strongswan.org/projects/strongswan/wiki/ForwardingAndSplitTunneling
# https://www.zeitgeist.se/2013/11/26/mtu-woes-in-ipsec-tunnels-how-to-fix/

iptables -P INPUT   ACCEPT
iptables -P FORWARD ACCEPT
iptables -P OUTPUT  ACCEPT

iptables -F
iptables -t nat -F
iptables -t mangle -F

# INPUT

# accept anything already accepted
iptables -A INPUT -m state --state ESTABLISHED,RELATED -j ACCEPT

# accept anything on the loopback interface
iptables -A INPUT -i lo -j ACCEPT

# drop invalid packets
iptables -A INPUT -m state --state INVALID -j DROP

# rate-limit repeated new requests from same IP to any ports
iptables -I INPUT -i "${ETH0ORSIMILAR}" -m state --state NEW -m recent --set
iptables -I INPUT -i "${ETH0ORSIMILAR}" -m state --state NEW -m recent --update --seconds 300 --hitcount 60 -j DROP

iptables -A INPUT -p tcp --dport "${SSHPORT}" -j ACCEPT

# VPN

# accept IPSec/NAT-T for VPN (ESP not needed with forceencaps, as ESP goes inside UDP)
iptables -A INPUT -p udp --dport  500 -j ACCEPT
iptables -A INPUT -p udp --dport 4500 -j ACCEPT

# forward VPN traffic anywhere
iptables -A FORWARD --match policy --pol ipsec --dir in  --proto esp -s "${VPNIPPOOL}" -j ACCEPT
iptables -A FORWARD --match policy --pol ipsec --dir out --proto esp -d "${VPNIPPOOL}" -j ACCEPT

# reduce MTU/MSS values for dumb VPN clients
iptables -t mangle -A FORWARD --match policy --pol ipsec --dir in -s "${VPNIPPOOL}" -o "${ETH0ORSIMILAR}" -p tcp -m tcp --tcp-flags SYN,RST SYN -m tcpmss --mss 1361:1536 -j TCPMSS --set-mss 1360

# masquerade VPN traffic over eth0 etc.
iptables -t nat -A POSTROUTING -s "${VPNIPPOOL}" -o "${ETH0ORSIMILAR}" -m policy --pol ipsec --dir out -j ACCEPT  # exempt IPsec traffic from masquerading
iptables -t nat -A POSTROUTING -s "${VPNIPPOOL}" -o "${ETH0ORSIMILAR}" -j MASQUERADE


# fall through to drop any other input and forward traffic

iptables -A INPUT   -j DROP
iptables -A FORWARD -j DROP

iptables -L

netfilter-persistent save

echo
echo "--- Configuring RSA certificates ---"
echo

mkdir -p /etc/letsencrypt

echo 'rsa-key-size = 4096
pre-hook = /sbin/iptables -I INPUT -p tcp --dport 80 -j ACCEPT
post-hook = /sbin/iptables -D INPUT -p tcp --dport 80 -j ACCEPT
renew-hook = /usr/sbin/ipsec reload && /usr/sbin/ipsec secrets
' > /etc/letsencrypt/cli.ini

certbot certonly --non-interactive --agree-tos --standalone --preferred-challenges http --email "${EMAILADDR}" -d "${VPNHOST}"

ln -f -s "/etc/letsencrypt/live/${VPNHOST}/cert.pem"    /etc/ipsec.d/certs/cert.pem
ln -f -s "/etc/letsencrypt/live/${VPNHOST}/privkey.pem" /etc/ipsec.d/private/privkey.pem
ln -f -s "/etc/letsencrypt/live/${VPNHOST}/chain.pem"   /etc/ipsec.d/cacerts/chain.pem

grep -Fq 'jawj/IKEv2-setup' /etc/apparmor.d/local/usr.lib.ipsec.charon || echo "
# https://github.com/jawj/IKEv2-setup
/etc/letsencrypt/archive/${VPNHOST}/* r,
" >> /etc/apparmor.d/local/usr.lib.ipsec.charon

aa-status --enabled && invoke-rc.d apparmor reload


echo
echo "--- Configuring VPN ---"
echo

# ip_forward is for VPN
# ip_no_pmtu_disc is for UDP fragmentation
# others are for security

grep -Fq 'jawj/IKEv2-setup' /etc/sysctl.conf || echo "
# https://github.com/jawj/IKEv2-setup
net.ipv4.ip_forward = 1
net.ipv4.ip_no_pmtu_disc = 1
net.ipv4.conf.all.rp_filter = 1
net.ipv4.conf.all.accept_redirects = 0
net.ipv4.conf.all.send_redirects = 0
net.ipv6.conf.all.disable_ipv6 = 1
net.ipv6.conf.default.disable_ipv6 = 1
net.ipv6.conf.lo.disable_ipv6 = 1
net.ipv6.conf.${ETH0ORSIMILAR}.disable_ipv6 = 1
" >> /etc/sysctl.conf

sysctl -p


echo "config setup
  strictcrlpolicy=yes
  uniqueids=never
conn roadwarrior
  auto=add
  compress=no
  type=tunnel
  keyexchange=ikev2
  fragmentation=yes
  forceencaps=yes
  # CNSA/RFC 6379 Suite B (https://wiki.strongswan.org/projects/strongswan/wiki/IKEv2CipherSuites)
  ike=aes256gcm16-prfsha384-ecp384,aes256gcm16-prfsha256-ecp256!
  esp=aes256gcm16-ecp384!
  dpdaction=clear
  dpddelay=900s
  rekey=no
  left=%any
  leftid=@${VPNHOST}
  leftcert=cert.pem
  leftsendcert=always
  leftsubnet=0.0.0.0/0
  right=%any
  rightid=%any
  rightauth=eap-mschapv2
  eap_identity=%any
  rightdns=${VPNDNS}
  rightsourceip=${VPNIPPOOL}
  rightsendcert=never
" > /etc/ipsec.conf

echo "${VPNHOST} : ECDSA \"privkey.pem\"
${VPNUSERNAME} : EAP \"${VPNPASSWORD}\"
" > /etc/ipsec.secrets

ipsec restart

echo
echo "--- Creating configuration files ---"
echo

mkdir -p "/home/${LOGINUSERNAME}" && cd "/home/${LOGINUSERNAME}"

cat << EOF > vpn-ios-or-mac.mobileconfig
<?xml version='1.0' encoding='UTF-8'?>
<!DOCTYPE plist PUBLIC '-//Apple//DTD PLIST 1.0//EN' 'http://www.apple.com/DTDs/PropertyList-1.0.dtd'>
<plist version='1.0'>
<dict>
  <key>PayloadContent</key>
  <array>
    <dict>
      <key>IKEv2</key>
      <dict>
        <key>AuthenticationMethod</key>
        <string>None</string>
        <key>ChildSecurityAssociationParameters</key>
        <dict>
          <key>EncryptionAlgorithm</key>
          <string>AES-256-GCM</string>
          <key>IntegrityAlgorithm</key>
          <string>SHA2-384</string>
          <key>DiffieHellmanGroup</key>
          <integer>20</integer>
          <key>LifeTimeInMinutes</key>
          <integer>1440</integer>
        </dict>
        <key>DeadPeerDetectionRate</key>
        <string>Medium</string>
        <key>DisableMOBIKE</key>
        <integer>0</integer>
        <key>DisableRedirect</key>
        <integer>0</integer>
        <key>EnableCertificateRevocationCheck</key>
        <integer>0</integer>
        <key>EnablePFS</key>
        <true/>
        <key>ExtendedAuthEnabled</key>
        <true/>
        <key>IKESecurityAssociationParameters</key>
        <dict>
          <key>EncryptionAlgorithm</key>
          <string>AES-256-GCM</string>
          <key>IntegrityAlgorithm</key>
          <string>SHA2-384</string>
          <key>DiffieHellmanGroup</key>
          <integer>20</integer>
          <key>LifeTimeInMinutes</key>
          <integer>1440</integer>
        </dict>
        <key>RemoteAddress</key>
        <string>${VPNHOST}</string>
        <key>RemoteIdentifier</key>
        <string>${VPNHOST}</string>
        <key>UseConfigurationAttributeInternalIPSubnet</key>
        <integer>0</integer>
      </dict>
      <key>IPv4</key>
      <dict>
        <key>OverridePrimary</key>
        <integer>1</integer>
      </dict>
      <key>PayloadDescription</key>
      <string>Configures VPN settings</string>
      <key>PayloadDisplayName</key>
      <string>VPN</string>
      <key>PayloadIdentifier</key>
      <string>com.apple.vpn.managed.$(uuidgen)</string>
      <key>PayloadType</key>
      <string>com.apple.vpn.managed</string>
      <key>PayloadUUID</key>
      <string>$(uuidgen)</string>
      <key>PayloadVersion</key>
      <integer>1</integer>
      <key>Proxies</key>
      <dict>
        <key>HTTPEnable</key>
        <integer>0</integer>
        <key>HTTPSEnable</key>
        <integer>0</integer>
      </dict>
      <key>UserDefinedName</key>
      <string>${VPNHOST}</string>
      <key>VPNType</key>
      <string>IKEv2</string>
    </dict>
  </array>
  <key>PayloadDisplayName</key>
  <string>IKEv2 VPN configuration (${VPNHOST})</string>
  <key>PayloadIdentifier</key>
  <string>com.mackerron.vpn.$(uuidgen)</string>
  <key>PayloadRemovalDisallowed</key>
  <false/>
  <key>PayloadType</key>
  <string>Configuration</string>
  <key>PayloadUUID</key>
  <string>$(uuidgen)</string>
  <key>PayloadVersion</key>
  <integer>1</integer>
</dict>
</plist>
EOF

grep -Fq 'jawj/IKEv2-setup' /etc/mime.types || echo "
# https://github.com/jawj/IKEv2-setup
application/vnd.strongswan.profile sswan
" >> /etc/mime.types

cat << EOF > vpn-ubuntu-client.sh
#!/bin/bash -e
if [[ \$(id -u) -ne 0 ]]; then echo "Please run as root (e.g. sudo ./path/to/this/script)"; exit 1; fi
read -p "VPN username (same as entered on server): " VPNUSERNAME
while true; do
read -s -p "VPN password (same as entered on server): " VPNPASSWORD
echo
read -s -p "Confirm VPN password: " VPNPASSWORD2
echo
[ "\$VPNPASSWORD" = "\$VPNPASSWORD2" ] && break
echo "Passwords didn't match -- please try again"
done
apt-get install -y strongswan libstrongswan-standard-plugins libcharon-extra-plugins
apt-get install -y libcharon-standard-plugins || true  # 17.04+ only
ln -f -s /etc/ssl/certs/DST_Root_CA_X3.pem /etc/ipsec.d/cacerts/
grep -Fq 'jawj/IKEv2-setup' /etc/ipsec.conf || echo "
# https://github.com/jawj/IKEv2-setup
conn ikev2vpn
        ikelifetime=60m
        keylife=20m
        rekeymargin=3m
        keyingtries=1
        keyexchange=ikev2
        ike=aes256gcm16-prfsha384-ecp384!
        esp=aes256gcm16-ecp384!
        leftsourceip=%config
        leftauth=eap-mschapv2
        eap_identity=\${VPNUSERNAME}
        right=${VPNHOST}
        rightauth=pubkey
        rightid=@${VPNHOST}
        rightsubnet=0.0.0.0/0
        auto=add  # or auto=start to bring up automatically
" >> /etc/ipsec.conf
grep -Fq 'jawj/IKEv2-setup' /etc/ipsec.secrets || echo "
# https://github.com/jawj/IKEv2-setup
\${VPNUSERNAME} : EAP \"\${VPNPASSWORD}\"
" >> /etc/ipsec.secrets
ipsec restart
sleep 5  # is there a better way?
echo "Bringing up VPN ..."
ipsec up ikev2vpn
ipsec statusall
echo
echo -n "Testing IP address ... "
VPNIP=\$(dig -4 +short ${VPNHOST})
ACTUALIP=\$(dig -4 +short myip.opendns.com @resolver1.opendns.com)
if [[ "\$VPNIP" == "\$ACTUALIP" ]]; then echo "PASSED (IP: \${VPNIP})"; else echo "FAILED (IP: \${ACTUALIP}, VPN IP: \${VPNIP})"; fi
echo
echo "To disconnect: ipsec down ikev2vpn"
echo "To reconnect:  ipsec up ikev2vpn"
echo "To connect automatically: change auto=add to auto=start in /etc/ipsec.conf"
EOF

cat << EOF > vpn-instructions.txt
== iOS and macOS ==
A configuration profile is attached as vpn-ios-or-mac.mobileconfig — simply open this to install. You will be asked for your device PIN or password, and your VPN username and password, not necessarily in that order.
== Windows ==
You will need Windows 10 Pro or above. Please run the following commands in PowerShell:
Add-VpnConnection -Name "${VPNHOST}" \`
  -ServerAddress "${VPNHOST}" \`
  -TunnelType IKEv2 \`
  -EncryptionLevel Maximum \`
  -AuthenticationMethod EAP \`
  -RememberCredential
Set-VpnConnectionIPsecConfiguration -ConnectionName "${VPNHOST}" \`
  -AuthenticationTransformConstants GCMAES256 \`
  -CipherTransformConstants GCMAES256 \`
  -EncryptionMethod GCMAES256 \`
  -IntegrityCheckMethod SHA384 \`
  -DHGroup ECP384 \`
  -PfsGroup ECP384 \`
  -Force
# Run the following command to retain access to the local network (e.g. printers, file servers) while the VPN is connected.
# On a home network, you probably want this. On a public network, you probably don't.
Set-VpnConnection -Name "${VPNHOST}" -SplitTunneling \$True
You will need to enter your chosen VPN username and password in order to connect.
== Android ==
Download the strongSwan app from the Play Store: https://play.google.com/store/apps/details?id=org.strongswan.android
Then open the attached .sswan file, or select it after choosing 'Import VPN profile' from the strongSwan app menu. You will need to enter your chosen VPN username and password in order to connect.
For a persistent connection, go to your device's Settings app and choose Network & Internet > Advanced > VPN > strongSwan VPN Client, tap the gear icon and toggle on 'Always-on VPN' (these options may differ by Android version and provider).
== Ubuntu ==
A bash script to set up strongSwan as a VPN client is attached as vpn-ubuntu-client.sh. You will need to chmod +x and then run the script as root.
EOF

EMAIL=$USER@$VPNHOST mutt -s "VPN configuration" -a vpn-ios-or-mac.mobileconfig vpn-ubuntu-client.sh -- "${EMAILADDR}" < vpn-instructions.txt

echo
echo "--- How to connect ---"
echo
echo "Connection instructions have been emailed to you, and can also be found in your home directory, /home/${LOGINUSERNAME}"

# necessary for IKEv2?
# Windows: https://support.microsoft.com/en-us/kb/926179
# HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\PolicyAgent += AssumeUDPEncapsulationContextOnSendRule, DWORD = 2