Securing a Network: How Effective Using Firewalls and VPNs Are?

Abstract

With the tremendous amount of increase in cyber threats on the Internet, the security of data traveling over a network has become a significant concern for all the netizens. As a result, a large number of Internet users have started using firewalls and VPN (Virtual Private Network) to ensure more protection for their data on the go. Though mostly considered as defenders of our network security, sometimes firewalls and VPNs can also pose some serious threats to its users. Our research focuses on addressing these security flaws by providing a specific illustration of the working principles and performance of the firewalls and VPNs, including the technologies behind them and their benefits, significant potential risks it may bring due to some considerable loopholes in their architecture, and the possible solutions to those security issues. We hope that our research will bring a better understanding of these security issues and their solution to help users and organizations to deal with these security threats and risks in a better way.

Full text

Securing a Network: How Effective Using
Firewalls and VPNs Are?
Sun Jingyao, Sonali Chandel
(&)
, Yu Yunnan, Zang Jingji,
and Zhang Zhipeng
New York Institute of Technology, Nanjing, China
{jsun19,schandel,yyu18,jzang,Zzhang36}@nyit.edu
Abstract. With the tremendous amount of increase in cyber threats on the
Internet, the security of data traveling over a network has become a significant
concern for all the netizens. As a result, a large number of Internet users have
started using firewalls and VPN (Virtual Private Network) to ensure more
protection for their data on the go. Though mostly considered as defenders of
our network security, sometimes firewalls and VPNs can also pose some serious
threats to its users. Our research focuses on addressing these security flaws by
providing a specific illustration of the working principles and performance of the
firewalls and VPNs, including the technologies behind them and their benefits,
significant potential risks it may bring due to some considerable loopholes in
their architecture, and the possible solutions to those security issues. We hope
that our research will bring a better understanding of these security issues and
their solution to help users and organizations to deal with these security threats
and risks in a better way.
Keywords: Firewall VPN Network security
1 Introduction
The importance of the Internet and its security was never as great of a concern as it is
now because of the amount of data that is exchanged through it 24 7. Plenty of
threats and risks exist in the cyber world that can affect the network security in a big
way. Hacking is one of the most common cyber threats to a network as it allows the
hackers aka malicious users to manipulate and attack the loopholes of vulnerable
networks and take control of it. Besides the external damage, which mainly reflects the
destruction caused by hackers by mostly using malware, virus or DDoS attacks, the
threat of resource openness because of using the computer network in a shared envi-
ronment, cannot be ignored at all. The exponential growth of security risks and dangers
that exists outside of a network in the present times can strictly confirm the necessity
for people to use and study the firewalls and VPNs so that the attacks can be prevented
and detected, and the network can be protected from getting damaged [1].
Firewall is a technology that is used to control the degree of interconnection
between different networks. It can prevent the external network from accessing the
internal network equipment and network resources using unauthorized ways. This
means a firewall can protect internal network and system from potential threats of a
©Springer Nature Switzerland AG 2020
K. Arai and R. Bhatia (Eds.): FICC 2019, LNNS 70, pp. 1050–1068, 2020.
https://doi.org/10.1007/978-3-030-12385-7_71
schandel@nyit.edu

network attack. This technology fully combines the potential of hardware and software
in a computer network and realizes active filtering and screening of potential threats
and risks to a network. A firewall usually is the first step to intercept an external attack
to accomplish the adequate protection for computer network security [2]. Figure 1[3]
introduce the connection schematic of Firewall, Intranet, and the Internet. The essential
features and primary functions of Firewalls are shown in Table 1[3].
A VPN is a virtual encrypted tunnel between the user and a remote server operated
by a VPN service. All external Internet traffic is routed through this tunnel, so our data
becomes safe from the data hunters. On the other hand, the IP address of the VPN
server becomes the user’s IP address, enabling them to hide their actual identity [4].
Firewalls are the gateways to ensure the security of the internal network and VPNs
are ways to access the internal network. There are always firewalls in the place where
there are VPNs. VPNs can be used with or without firewalls, but they are not rec-
ommended to be implemented without firewalls as their primary purpose is to secure
the network traffic. A VPN without a firewall makes VPN’s encryption function use-
less. Using VPN with firewall further enhances the security of the Internet and network
in general.
Fig. 1. The connection schematic of a Firewall, Intranet, and Internet
Table 1. The basic features and main functions of a firewall
Basic features Main functions
All network data between the external and internal networks
must pass through the firewall
Firewall is a barrier to
network security
Only data flows that conform to security policies can pass
through a firewall
It can strengthen network
security strategy
It can monitor and audit
network access
The firewall itself should have powerful immunity against
attacks
It prevents leakage of
internal information
Securing a Network: How Effective Using Firewalls and VPNs Are? 1051
schandel@nyit.edu

This paper aims to provide a detailed study of the security issues and its solutions
that the users of a Firewall and a VPN should know. In this paper, we have proposed
some suggestions for the safety and security in using the Firewalls and VPNs based on
the literature survey that we did for our research. This paper is structured as follows:
Related work is mentioned in Sect. 2. In Sect. 3, an overview of the firewall and VPN
technologies has been discussed. Section 4introduces the security issues related to
using firewalls and VPNs. The most common threats and attacks in using firewalls and
VPNs are discussed in Sect. 5. Solutions for the most common security issues in using
firewalls and VPNs has been discussed in Sect. 6. In Sect. 7, the conclusions are
drawn, and future work has been mentioned.
2 Related Work
In the past, the authors of [1,3,26,30] focused on the security of firewalls and VPNs,
but they did not discuss anything regarding the attacks or threats on firewalls and
VPNs. [2] does not provide some specific methods about how to improve the security
issues of firewalls. The authors of [9] and [12] present just one case study and focus on
one aspect. [9] focuses on an example of a system using both Firewall and VPN. It
presents a case of two firewalls with the same configuration in the same network node,
which communicate with each other through a direct connection. [12] focuses only on
the deep packet inspection technology of firewall. Furthermore, paper [10] is an old
study that does not cover the recent problems and various attacks that happens in the
cyber world presently. Paper [13] also talks about one model without its realization. In
addition, some papers like [17,19,20,24–26] only concentrate on one attack rather
than its relationship with the firewalls. The work done by us will not only analyze
firewalls and VPNs individually, but we will also compare them together to enhance
their abilities in providing more security. It also means that the security loopholes and
the solution will be related to both of them. We will analyze the better structure or
system concerning the latest products like Web Application Firewall, Secure Web
Gateway, and Next Generation Firewall to find the reasons behind them for being
considered as safer than traditional firewalls and VPN setups.
3 The Working Principles of Firewalls and VPNs
3.1 The Working Principle of Firewalls
Firewall technology has been developing continuously since its birth. Various kinds of
firewalls with different structures and functions are built into a network for getting more
defense. Traditional firewall technology falls into three categories, and no matter how
sophisticated the implementation of a firewall is, it is ultimately based on the following
three technologies.
1052 S. Jingyao et al.
schandel@nyit.edu

3.1.1 Packet Filtering
The working principle behind the Packet filtering firewall can be called as a network
firewall because it works in the network layer. It usually decides whether to let the data
packets pass, by examining the address, protocols, and ports of each packet. Figure 2
shows the principles of Packet filtering. The packet filter can be divided into a static
packet filter and dynamic packet filter [5].
•Static packet filter. Static packet filter technology is a traditional packet filter. It
decides whether these data packets can be passed according to the IP addresses of
these data packets. If attackers set their mainframe IP addresses as legal addresses,
they can quickly pass the static packet filtering firewall. Therefore, this kind of
firewall is not secure enough.
•Dynamic packet filter. It can automatically apply to create or delete packet filter
rules according to dynamic practice application without administrators’interven-
tion. However, the dynamic packet filter technology can only filter against data’sIP
address instead of the legality of users. It also does not have log records to check
which brings enormous difficulties to daily network security management. There-
fore, it has been replaced by a new technology called the Adaptive Proxy Protection
firewall.
3.1.2 Application Proxy
Application Proxy firewall is also called as an Application Gateway firewall. This
firewall participates in the entire process of a TCP connection through Proxy tech-
nology. The data packets sent from the inside are processed by the firewall to hide the
Intranet structure. Network security experts recognize this type of firewall as the most
secure firewall. Its core technology is the proxy server technology. The proxy server
refers to the program that represents the client’s connection request on the server. When
the proxy server gets connection intentions from a client, they will verify the client’s
request and then handle connection requests through the specific secure proxy
Fig. 2. The principle of packet filtering
Securing a Network: How Effective Using Firewalls and VPNs Are? 1053
schandel@nyit.edu

applications. The request is transferred to the real server, which then accepts the server
response. After further processing, the proxy will reply to the final client who makes a
request. The proxy server plays the role of interconnecting the application of the
external network to the internal network [5].
Adaptive Proxy Firewall
Adaptive proxy is a revolutionary technology implemented recently in commercial
application firewalls. It combines the advantages of the safety of the Application Proxy
firewall and the high speed of packet filtering firewall and improves the performance of
the proxy firewall by ten times without losing the security.
3.1.3 Stateful Inspection
Stateful Inspection is an extension of the packet-by-packet filtering process, which
tracks individual flows, enabling policy checks that extend across a series of packets
[6]. It checks the handshakes in a communication network by exploiting detailed
information of the communication protocol. It detects malicious activities by moni-
toring packet-by-packet connection and predicting the next move based on what
happened. This makes it a more advanced tool than other firewalls [7]. These firewalls
maintain a table of open connections, inspecting the payload of some packets and
intelligently associating new connection requests with existing legitimate connections
[8]. With modern firewalls, network administrators can control the network trafficina
more fine-grained fashion.
3.2 The Working Principle of VPNs
The mainstream applications that claim to provide VPN services are using one of the
following three techniques [4]:
•Proxy Server. A proxy server is like a courier service that is responsible for only
transcending the messages. The work of proxy servers is conducted in the HTTP
layer and the Socket layer in the Open System Interconnection (OSI) model under
most circumstances. Figure 3explains how proxy server functions.
Fig. 3. The working architecture of a proxy server
1054 S. Jingyao et al.
schandel@nyit.edu

•IPSec. IP Security (IPSec) is the most common method used by the VPN appli-
cations. It works in the third layer called the Network layer of the OSI model.
•SSH. An encrypted channel needs to be combined with the proxy server to over-
come the blocked network. The tool that is used to scale the blocked network called
SSH is, in fact, an SSH agent. In the TCP/IP 5-tier model, SSH is the security
protocol that applies to the application layer and the transport layer. SSH is a remote
shell, an application based on SSL. Although many people use SSH to transmit
data, they merely use the SSL proxy function of SSHD software to get this job
done.
3.3 Architecture of a System Using a Combination of Firewall and VPN
Figure 4shows a typical network security architecture based on the combination of
both firewall and VPN technology [9]. The system has a master node under which there
are large nodes and links between them. Under the big node, there are intermediate
nodes, and under the intermediate nodes, there are small nodes. The intermediate node
and the small node is only connected with its own upper and lower levels. Between
nodes, individual wire connections can also support other ways of connecting people,
such as wireless connections. Security between nodes ensures the safe transmission of
data through the virtual encryption channel between VPN array devices and VPN
receiver devices.
The entire network adopts a network management system to manage, control and
report congestion for various security devices, routers, switches and servers in the
network, as well as fault management. The network management system will monitor
equipment utilization, bandwidth utilization, packet loss rate, etc. Two firewalls with
the same configuration are used in the same network node, and they communicate with
each other through a direct connection. Under normal circumstances, one is working,
which is the primary, and the other is in the backup state.
Fig. 4. A typical network security architecture based on firewall and VPN technology
Securing a Network: How Effective Using Firewalls and VPNs Are? 1055
schandel@nyit.edu

High availability is achieved through “heartbeat”mode. A direct connection
between two firewalls of the same type creates the heartbeat line that uses fixed interval,
master-slave equipment to exchange information. When the host accidentally crashes, or
network fails, hardware failure happens. Master-slave firewall switch is a working state
from the machine instead of the standard work of the host, to guarantee the regular use of
the network. Switching process does not require a human operator. They also do not
need the participation of other systems. The primary firewall’s restore function will
automatically return the control to the firewall, to assure the safety of the network. By
deploying this network security system with firewall technology as the core, a VPN can
realize the secure exchange of confidential information between nodes.
4 Security Issues in Using Firewalls and VPN
Even though firewalls and VPNs are used for protecting or mitigating the external
attacks on a network or a system, but they are not full proof. In this section, we will
discuss some of the shortcomings in both of these technologies.
4.1 Security Issues of Firewalls
With the increasing severity of network security issues and the continuous development
of security defense, shortcomings of firewalls in the security aspect have gradually
attracted much attention from security researchers and organizations. Due to the
existing loopholes in the firewall architecture, a series of attacks can quickly destroy a
network. Analyzing firewall’s vulnerabilities and the attacks against it is of great
significance to the development and improvement of firewall technology for complete
network security.
The most common security flaws of firewalls are as follows:
•Firewalls may sacrifice some useful network services. Firewall’s“either in or
out”feature is bound to shut down some valuable ports due to security problems,
sacrificing some helpful network services as well [10]. After the firewall receives
network packets at the network layer (including the following link layer), it matches
them one by one based on the rules. It then performs prearranged actions if they are
consistent, such as allowing or denying packet access. This creates a lot of dis-
comfort and challenges for the organizations and users alike to make sure that the
good packets are not misunderstood and blocked as bad ones.
•Firewalls cannot protect against attacks from internal network users. Firewalls
are the outlet for information between different networks or network security
domains. It can control the flow of information in and out of the network according
to the set security policy. This prevents the illegal information from flowing into the
protected network without affecting the regular access of the protected network to
the Internet. This feature of firewall determines that it can only filter packets
between internal and external networks but cannot process packets from within the
internal networks [11]. This makes it impossible to protect against attacks from
internal network users commonly known as insider threats.
1056 S. Jingyao et al.
schandel@nyit.edu

•Firewalls are not secure against software or files with the virus. Firewall for
encrypted SSL stream of data is not visible. This means that the firewall cannot
quickly seize the SSL data flow and do the decryption. Therefore, it cannot stop the
attack of the application as well as cannot see the application firewall’s encrypted
data [12]. The firewall can recognize and intercept attack data only when the
attacking behavior of the application layer matches the existing attacking behavior
of the database in the firewall.
•Afirewall cannot extend depth detection. It is impossible for a general firewall to
extend depth detection that is based on the data package without increasing network
performance accordingly. Profound detection capabilities for all network and
application traffic require unprecedented processing power to accomplish a large
number of computing tasks; including (1) SSL encryption/decryption function
(2) Complete two-way payload detection (3) Ensure the normalization of all
legitimate traffic (4) Extensive protocol performance. These tasks cannot run effi-
ciently on standard PC hardware [13].
The weaknesses of five general kinds of firewalls are shown in Table 2[13].
4.2 Security Issues of VPNs
Any company or organization that implements a VPN to ensure their network security
still cannot ignore the risks and threats that can destroy or sabotage their network
without them even knowing or realizing it. The most common risks can be seen in
Table 3.
Table 2. The weaknesses of five general kinds of firewalls
Firewalls Weaknesses in the security system
Packet filtering firewall Hard to configure
Status/dynamic detection firewall Delay in the network connection
Web application firewall Limited range of user system
Network address translation
firewall
Unable to mitigate the internal attacks and threats
Personal firewall Unable to monitor and control multiple
communication
Table 3. The risks involved in using a VPN
1 Securing against lateral network movement
2 Securing and connecting to cloud-based infrastructure
3 Blocking malicious insiders, over-privileged users, and compromised third-party access
4 Preventing malware from proliferating across the network
5Efficiently integrating with business processes and identity management systems
Securing a Network: How Effective Using Firewalls and VPNs Are? 1057
schandel@nyit.edu

IPSec VPN: This VPN has a robust communication protocol and encryption
algorithm, so its security issues mainly come from its client’s attacks [14].
•The local security configuration is not perfect: The users control the local security
configuration of the VPN’s client-side themselves. It means there might be some
security risks caused by human factors. For example, some clients may keep the
license certificate on the local device. Once the attacker gets the control of these
devices, they can open a VPN channel without even needing a login name and the
password and bypass the authentication process altogether.
•Stealing VPN security information: Attackers can steal VPN security information
by using social engineering methods such as phishing. This security information
includes the IP address of the VPN client, configuration parameters, user license
certificates, etc. The attacker can forge a communication identity and pose a threat
to the security of a VPN by using this security information.
•The internal security of VPN is weak: The security protection requirements for
trusted users are relatively low after VPN is successfully connected. Because there
is no attack prevention strategy in the tunnel that decreases the security risk within
the VPN.
SSL VPN: This VPN does not require specialized client software, but they use web
browsers for its implementation. Therefore, the security threats of SSL VPNs are
mainly focused on browsers and servers.
•Security problems caused by incorrect system operation: If the user does not close
the SSL VPN by logging out at the end of the browser and the server process, it may
keep the SSL VPN server process open. The attacker can use this situation to bypass
authentication and access the VPN, which brings a high-security threat to the VPN
system.
•Malicious attacks on identity authentication: SSL VPNs allow users to log on to
the VPN system from any location through a browser. This increases the risk of
leaking security information such as login id and passwords, especially when they
log in from public places.
•The virus infects the internal network through the tunnel: SSL VPN remote users
can use any location of any client remote login within the enterprise network. Once
the viruses at client-side connect to the internal network, the infected file will be
able to use the SSL VPN tunnel to invade the internal network. At the same time,
due to the limitations of the internal network boundary of the firewall, it cannot
prevent the transmission of infected software or files effectively. As a result, the
virus can infect the internal network through the tunnel.
•The security risks of the Web server itself: Most of the SSL VPN system use Web
server as its underlying platform. Therefore, the potential safety hazard of the Web
servers, such as the back door or unauthorized leaks will also bring serious security
problems to the SSL VPN system [14].
MPLS VPN: This VPN has adopted a strict routing information isolation mech-
anism. The security of user information transmission is guaranteed by using
1058 S. Jingyao et al.
schandel@nyit.edu

MPLS VPN. However, as a technology based on IP communication, its transmitted
information is not encrypted and authenticated, so there are still some security prob-
lems that exist in MPLS VPN [14].
•Attacks against VPN routing devices. This attack usually occurs during the routing
information release phase. The attacker disguised as an edge device establishes a
session with the server equipment to connect and exchange routing information.
This will cause the disclosure of the VPN’s internal routing information. The
attacker can also forge or tamper with the routing information to spread the user’s
data in the wrong direction to eavesdrop and steal the user’s personal information.
•Security threats from the Internet. In the case of users accessing the Internet
through MPLS VPN, the attackers can attack the network by traditional attack
means such as IP source address deception, session hijacking, and planting Trojan
horse in the network. The user’s data flow will be viewed, modified, forged and
deleted by the hackers without their knowledge.
4.3 The Loopholes in Using Firewalls with VPNs
The firewalls with VPNs can provide a virtual private network on the unsafe Internet
through the VPN function. Therefore, it can guarantee the security of the confidential
data of the enterprise when the remote access happens. However, at the same time,
there will be many loopholes in using this arrangement of firewalls with VPNs. The
loopholes in using firewalls with VPNs are shown in Table 4[15].
5 Using Firewalls and VPNs: The Most Common Attacks
and Threats
5.1 The Attacks and Threats of Using Firewalls
Generally, the most common attacks happen to the Packet Filtering Firewalls and the
Status/Dynamic Detection Firewalls [16]. In Table 5, we list the attacks that could
corrupt the firewall security.
The IP Spoofing Attack. It can easily make use of a legal address from the
ordinary users. Attackers can avoid an authentication process provided by the firewall
using this way and hide. Also, when attackers use spoofing attack, this behavior of
hackers will make the log, and NAC (Network Access Control) will point to the wrong
person when used to track down the attackers. This kind of MAC (Medium Access
Control) attack is straightforward to create and can facilitate a variety of advanced
attacks [17].
Denial of Service (DoS). Unlike many other attacks, DoS attack is purely mali-
cious because the hackers gain nothing personal from the attack. They attack the user’s
system with the aim of depriving the system’s working ability. To overload the victim
network, the hackers send large data that floods the system. To send data, they usually
need to know the IP address of the targeted network, but firewalls with VPN can hide
the IP address and block the malicious data package.
Securing a Network: How Effective Using Firewalls and VPNs Are? 1059
schandel@nyit.edu

Table 4. The loopholes in using firewalls with VPNs
Contents Loopholes
Firewall rule virtual test No work can detect the effect of the configured strategy
Intranet service permissions
settings
No function
Quality of service loan allocation In general, there is no VPN within QoS permissions
Multi-line superposition and
backup of firewalls and VPNs
Only double backup
VPN maximum transmission unit Manually modify maximum transmission unit based on
the Internet environment
VPN dynamic IP addressing We can only use dynamic domain name system and other
third party’s solutions. People control the use
Hardware binding authentication No function. Only username, and password
USB key security policy storage
and exchange
Only security certificates can be stored, and clients still
need professional staff
Support for mobile users Not supported or incorporated into through the PPTP
protocol with little support and inadequate security
Protocol, encapsulation, and
compression
Standard IPSec, using the network address translation
standard. User datagram protocol encapsulation ensures
that data is correct with other check fields. One by one
packet encapsulation and no compression technology
lead to low bandwidth utilization
VPN performance Using low-end hardware components. Single channel
connection speed is slow. The number of access support
is limited, and performance is unprotected
Support for VPN channels Unable to support a large number of branches and client
access, network performance significantly decreased
when there are more nodes
Software No software VPN gateway
Convenience of implementation It is complicated that it needs professional staffing
Support for access methods It can only access with Internet IP and does not support
new access modes such as cell broadband, WLAN, and
GPRS
Table 5. The most common attacks on firewall
Types of firewall Attack
Packet filtering IP spoofing attack
Denial of service
IP fragmentation attacks
Trojan attacks
Status/dynamic detection firewall Protocol tunnel attack
Passive FTP
Rebound Trojan attack
1060 S. Jingyao et al.
schandel@nyit.edu

IP Fragment Attack. In an IP fragment package, only the first fragment has the
information of the TCP port. When the package is transmitted through the Packet
Filtering Firewall, the firewall only checks the first fragment to decide whether to let it
pass. In this case, the attacker can cheat the firewall by sending a legitimate first IP
fragment, and then the rest of the malicious fragment can pass through the firewall and
cause a threat to the network security [18].
Trojan Attack. It is the most effective attacking method to Packet Filtering Fire-
wall because once the Trojan is installed inside the network, there is nothing a firewall
can do to stop it. The reason is that the Packet Filtering Firewall usually only filter the
packet at the lower port (1-1024) and most Trojan attacks through the higher ports [19].
Protocol Tunnel Attack. The attack of the protocol tunnel is similar to the idea of
a VPN, and the attacker hides some malicious attack packets in the head of some of the
protocols, so it can penetrate the firewall system and attack the internal network [20].
Passive FTP. It solves the issue of an FTP client’sfirewall blocking incoming
connections. “PASV”is the command that is used by the FTP client to let the server
know that it is in passive mode. This is a preferred mode for FTP clients behind a
firewall and is often used for web-based FTP clients and computers connecting to an
FTP server within a corporate network [21].
Rebound Trojan. The internal network’s rebound Trojan periodically connects to
a host controlled by an external attacker. Since the connection is initiated from within,
the firewall considers it as a legitimate connection, causing the blind area of the
firewall. A firewall cannot distinguish between a Trojan’s connection and a legitimate
connection. The limitation of this attack is that the Trojan must be installed inside the
network first [22].
5.2 The Attacks and Threats to a VPN
Choosing a VPN is a good idea to get protection against a network, especially when it
is a public Wi-Fi. However, use of a VPN can sometimes be a threat to security and
bring some risks as well. VPN establishes a channel between the user and the server, so
the user’s trust in the VPN provider is essential because the provider can see and record
all the data and can even alter the content. If a VPN is not configured correctly, a
hacker might be able to access the user’s local LAN directly, which is worse than being
exposed to public Wi-Fi. For example, GoGo, a VPN provider was accused of using
fake YouTube certificates that could leak users’passwords [23].
•Man in the Middle Attack (MITM). Some VPN providers adopt pre-shared key
for their users, and that can lead their users to be caught up in a Man in the Middle
attack (MITM). In the MITM attack, there are two endpoints of victims, and the
attackers are third-party. The attackers can access the communication channel
between two endpoints and manipulate the messages [24]. MITM attack aims to
compromise the following three targets [25]:
•Confidentiality: It can be achieved by eavesdropping on the communication.
•Integrity: Attackers can intercept the communication and modify messages.
•Availability: By intercepting and destroying messages or modifying messages,
attackers can make one of the party to end communication.
Securing a Network: How Effective Using Firewalls and VPNs Are? 1061
schandel@nyit.edu

•Hacking or Eavesdropping. It includes physical access or listening to the devices
that support VPNs. This can happen if someone loses their laptop or mobile device,
which supports VPNs. Most VPN applications are not configured for the best
security model, and the local license is stored in the device itself. In this case, the
hackers can access the VPN channel without entering a password.
•Unauthorized Access to the VPN Data. Obtaining secure information from a VPN
is a third way in which VPN security may be corrupted. This security information
includes IP addresses, configuration parameters and user license certificates for a
VPN terminal. Access to this information may come from the insiders who know
the specifics of a VPN, such as, people who have left or have been fired from the
company. Most networks do not change frequently, and VPN connections remain in
the same state for a long time. Therefore, people leaving the company have many
opportunities to learn about specific ways to access the VPN. This security infor-
mation can also be obtained through other social engineering methods, such as
phishing or vishing.
•Exploit Vulnerabilities in the System. A possible defect in the firmware itself or
some other weakness of the authentication system can be exploited, such as,
malicious spoofing or redoing SSL authentication. It would even be possible for a
hacker to use these well-known vulnerabilities in the VPN concentrator to crash the
authentication system to invade the target system [5].
6 The Solutions for the Security Issues of Firewalls and VPN
6.1 The Solutions for the Security Issues of Firewalls
The Immune-Based Firewall System. After an intruder bypasses a firewall, they must
control the firewall system or break the work of the firewall system. To achieve this
goal, they must destroy the vital information of the firewall. Therefore, the immune-
based firewall system security model centers on the critical information files of the
firewall and uses the change of these files as a means to determine whether there is an
intrusion. Because the intrusion is the “differences”in the firewall system.
The critical information file is the body of the firewall system. If an intruder
destroys the body of the firewall system, the firewall will find and resist it to protect the
critical files that are on record. It will also record the destruction and control of the
network communication. The basic structure of the system security model is shown in
Fig. 5[26], centered on the critical information file of a firewall and file information
database. It also uses the immune subsystem as the core to build a relatively perfect
firewall system. However, when it comes to the actual application effect, the filtering
mechanism of the firewall against these attacks is still not perfect yet, and there is no
effective strategy to solve this problem. An ideal firewall filtering mechanism and the
security policy model is shown in Fig. 6[26].
Multi-Stage Filter. The Multi-stage filter uses multilevel filtering in the firewall to
filter out all source routing packets and the fake IP sources at the level of packet
filtering. The multi-stage filter is a technology that is now widely used by firewalls as
1062 S. Jingyao et al.
schandel@nyit.edu

packet filtering to efficiently help the protection of firewalls. This method is evident in
the layer and can expand many new contents from this concept.
Next Generation Firewall. Next-Generation Firewall (NGFW) is the latest buzz in
the firewall market at present. Through in-depth insight into users, applications, and
content in network traffic, and with the help of a new high-performance single-path
heterogeneous parallel processing engine, NGFW can provide users with active
application layer integrated security protection. It can help users to conduct business
safely and simplify their network security architecture. Application recognition is the
most critical technology in the route. The technical route of NGFW is shown in
Fig. 7[27].
Secure Web Gateway. Secure Web Gateway (SWG) is a kind of product solution
for Internet exploitation. It has the functions like URL filtering, malicious code pro-
tection, control functions, and the application control functions including the Web
functions. This means it can enforce the enterprise’s Internet access strategy while
protecting it from the security threats. Most of the mainstream SWG products also
Fig. 5. The model of immune-based security firewall
Fig. 6. Protocol-based firewall security policy model
Securing a Network: How Effective Using Firewalls and VPNs Are? 1063
schandel@nyit.edu

provide the user identification and the DLP (Data Leakage Protection) function on this
basis. Some company such as Intel uses SWG to protect their company’s security.
Figures 8and 9shows the structure of SWG firewall [28].
Fig. 7. Technical route of NGFW
Fig. 8. The hardware structure of embedded gateway
Fig. 9. The overall structure of gateway software
1064 S. Jingyao et al.
schandel@nyit.edu

Web Application Firewall. Web Application Firewall (WAF) is mainly used to
strengthen protection against web-specific intrusion methods such as DDoS attacks,
SQL injection, XML injection, XSS, etc. WAF can be divided into front-end capture,
rule setting and monitoring (brain), regulation action (monitoring or blocking), log
storage/monitoring display, and corresponding processing unit as shown in Fig. 10
[29]. Currently, there are three types of WAFs in the market, namely: Hardware Web
firewall, Web protection software and Cloud WAF.
6.2 The Solutions for the Security Issues of VPNs
Wi-Fi wall. It is a useful technology to protect the VPNs when the user connects to the
Wi-Fi. This technology can monitor the Wi-Fi traffic, and it can constantly check if
there are attacks. The Wi-Fi wall will disconnect the Wi-Fi once an attack is detected.
Authentication service. The VPN service providers need the authentication service
to help them to protect the identity information about the potential end-users [30].
Access control. This service can maintain the security and prevent the use of
unauthorized VPN service features and access to the unauthorized resources [30].
Data integrity and confidentiality. This service can keep the integrity of infor-
mation, prevent the leakage of information, and counter threats. The cryptographic
hardware can protect the integrity and confidentiality of management data [30].
VPN audit requirement. The suitable auditing system is necessary to detect
potential abuse, since the present security service and security mechanisms may be
compromised or bypassed. Therefore, the hackers may gain the unauthorized access
Fig. 10. WAF working principle
Securing a Network: How Effective Using Firewalls and VPNs Are? 1065
schandel@nyit.edu

and damage the VPN protected by them. Enumerating and understanding the VPN
service behavior is necessary for providing enough information for studying the VPN
auditing requirements [30].
VPN firewall. VPN Firewall is a kind of firewall that is installed at the server end
or the front of a VPN server. It is configured with the filters only to let the VPN specific
packets to access the network when installed at the server end of the VPN. However,
when it is installed at the front of a VPN, it will only allow the tunnel data on its
Internet interface to access the server [31].
HAIPE security gateway. In this model, VPN client edge device is intended to use
network hardware encryption device HAIPE as a security gateway to protect the
communication between VPN client sites. It is shown in Fig. 11 [32] that the VPN user
network consists of A and B stations. The edge of station A is deployed with the
HAIPE_A security gateway, and the edge of station B is deployed with the HAIPE_B
security gateway. HAIPE_A and HAIPE_B are equal and establish ESP (Encapsulating
Security Payload) encrypted tunnel between them, which let any information stream
between station A and station B be protected by the ESP encrypted tunnel. Only the
flow of the network to peer protection or the flow of the network from the peer
protection network will pass through the gateway, and the rest of the traffic is stopped
by the secure gateway of ESP encrypted tunnel.
7 Conclusion and Future Work
As a result of this study, we have concluded that the potential threats and risks to the
Internet and Intranet will keep growing and so does the development of firewalls and
VPNs. With the increased implementation of technology in almost all possible domains
of cyberspace, the security and protection of a network will need more attention with
time. We also realized that the gap between the potential threats and the risks to these
Fig. 11. Diagram of HAIPE security gateway protecting plain text (PT) domain communication
1066 S. Jingyao et al.
schandel@nyit.edu

systems are growing exponentially and the present-day firewalls and VPNs are not full
proof yet. This results in defeating their purpose sometimes.
We also concluded that it is not easy to judge firewall or VPN against each other
because there are many types of firewalls and VPNs available in the market and each
one of them has its advantages and disadvantages. The kind of users and their demands
regarding how much safety they want in their network and how much budget do they
have to get what they need in a firewall or VPN is also the key in its implementation.
A combination of firewalls and VPNs can always provide more security to a network
than using them individually. The users also need to keep in mind that both VPNs and
firewalls have quite a few security flaws and there are various solutions available to
avoid these loopholes. Our advice is to consider the application environment and the
user’s expectation of performance carefully when choosing a firewall or a VPN or both
for creating a secure network system. However, there are still some parts that we did
not cover in this paper. Our following plan for this topic is to study some methods that
can deal with the security issues both related to firewalls and VPNs since we have
already researched the security threats, risks, and issues that both firewalls and VPNs
have.
In all, we hope that our work can be used as a reference by the organizations and
individuals when it comes to the solutions for the loopholes, threats, and risks related to
afirewall and a VPN. Further study needs to be done to make a unified model of a
secure firewall and VPN to fight the attacks and the attackers and save the data and the
network from being destroyed or breached.
References
1. Ma, L., Liang, H.: Application of firewall technology in computer network security. Comput.
Knowl. Technol. 10, 3743–3745 (2014). Print
2. Jiang, C.: Research on computer network security technology and firewall technology.
Ability Wisdom 235 (2017). Print
3. Su, J., Yuan, J.: Firewall technology and its development. Comput. Eng. Appl. 147–149
(2004)
4. Zhang, Z., et al.: VPN: boon or trap? A comparative study of MPLS, IPSec, and SSL virtual
private network. In: ICCMC 2018 (In Press)
5. Sun, J., Wei, J.: Computer Network Technology and Application. Xi’an University of
Electronic Science and Technology, Xi’an, China (2010)
6. Stateful-inspection firewall: the Netscreen way. http://www.netscreen.com/products/
firewallwpaper.html
7. Li, S., Tørresen, J., Sorensen, O.: Exploiting Stateful Inspection of Network Security in Re-
Configurable Hardware
8. Suehring, S.: Linux Firewalls: Enhancing Security with Nftables and Beyond, Illustrated
edn, p. 25. Pearson Education (2015). ISBN 0134000021
9. Successful case: Hanbo firewall to build a safe and efficient enterprise Intranet. Network
World 2011-12-12 (021) (2011)
10. Qing, Y.: Shortcomings and improvements in firewall security. Sci. Technol. Eng. 14, 1009–
1012 (2005)
Securing a Network: How Effective Using Firewalls and VPNs Are? 1067
schandel@nyit.edu

11. Sun, K.: Concrete application of firewall technology in computer network security. Sci.
Technol. Econ. Guide 17, 38 (2017)
12. Wang, D.: Research on Deep Packet Inspection Technology of Firewall. Xi’an University of
Electronic Science and Technology (2005)
13. Zhang, T.: Design and Implementation of Firewall Based on Content Filtering Software.
University of Electronic Science and Technology (2012)
14. Security analysis of VPN technology, 19 Sept 2014. Web. http://sec.chinabyte.com/368/
13082868.shtml
15. Comparison between professional VPN and firewall with VPN. Web. https://wenku.baidu.
com/view/6e89ab1055270722192ef791.html
16. Network security: a simple guide to firewalls. In: Network Security, pp. 2–3 (2000)
17. Yadav, A.S.S., et al.: Prevention of spoofing attacks in wireless networks. In: International
Conference on Computing Communication Control and Automation, pp. 164–171. IEEE
(2015)
18. Hollis, K.: The Rose Attack Explained. Retrieved on 2013-11-25
19. Sakurai, S., Ushirozawa, S.: Input method against Trojan horse and replay attack. In: IEEE
International Conference on Information Theory and Information Security, pp. 384–389.
IEEE (2010)
20. Chen, D., Wang, P.: Study and implementation of tunnel attack in MANET. Comput. Eng.
33(9), pp. 140–141 (2007)
21. What is PASV FTP (passive FTP)? 13 Jun 2018. Web. https://www.lifewire.com/definition-
of-passive-mode-ftp-816441
22. Zhao, T.F., et al.: Detecting rebound port Trojan based on network behavior analysis.
Netinfo Secur. (2011)
23. VPN helps you scale the wall? Let’s put our privacy first, 6 Jun 2016. Web. https://www.
jb51.net/hack/471867.html
24. Conti, M., Dragoni, N., Lesyk, V.: A survey of man in the middle attacks. IEEE Commun.
Surv. Tutor. 18, 2027–2051 (2016)
25. Khan, M.M., Bakhtiari, M., Bakhtiari, S.: An HTTPS approach to resist man in the middle
attack in secure SMS using ECC and RSA. In: 2013 13th International Conference on
Intelligent Systems Design and Applications, pp. 115–120, Dec 2013
26. Yang, Z., Cheng, Q.: Research of immune-based technology for the firewall system security.
Microcomput. Inf. 21, 9-3
27. Network behavior management and the next generation of firewalls, SWG relations. Web.
https://jingyan.baidu.com/article/cbf0e50095f63a2eaa2893cc.html
28. Zhao, Y., Du, Y.: Design and implementation of embedded secure web gateway. Comput.
Eng. Des. 27(4) (2006)
29. Sahin, M., Sogukpınar, I.: An efficient firewall for web applications (EFWA). In: 2017
International Conference on Computer Science and Engineering (UBMK), pp. 1150–1155
(2017)
30. Boukari, N., Aljane, A.: Security and auditing of VPN. In: Proceedings of Third
International Workshop on Services in Distributed and Networked Environments,
pp. 132–138, 6 Aug 1996
31. VPN firewall. Techopedia. 28 Jun 2017. Web. https://www.techopedia.com/definition/
30753/vpn-firewall
32. Dian, A.: Security research and improvement of mainstream VPN technology (2009)
1068 S. Jingyao et al.
schandel@nyit.edu