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Without security measures and controls in place, your data might be subjected to an attack. Some attacks are passive, meaning information is monitored; others are active, meaning the information is altered with intent to corrupt or destroy the data or the network itself.
Your networks and data are vulnerable to any of the following types of attacks if you do not have a security plan in place.
In general, the majority of network communications occur in an unsecured or "cleartext" format, which allows an attacker who has gained access to data paths in your network to "listen in" or interpret (read) the traffic. When an attacker is eavesdropping on your communications, it is referred to as sniffing or snooping. The ability of an eavesdropper to monitor the network is generally the biggest security problem that administrators face in an enterprise. Without strong encryption services that are based on cryptography, your data can be read by others as it traverses the network.
After an attacker has read your data, the next logical step is to alter it. An attacker can modify the data in the packet without the knowledge of the sender or receiver. Even if you do not require confidentiality for all communications, you do not want any of your messages to be modified in transit. For example, if you are exchanging purchase requisitions, you do not want the items, amounts, or billing information to be modified.
Most networks and operating systems use the IP address of a computer to identify a valid entity. In certain cases, it is possible for an IP address to be falsely assumed— identity spoofing. An attacker might also use special programs to construct IP packets that appear to originate from valid addresses inside the corporate intranet.
After gaining access to the network with a valid IP address, the attacker can modify, reroute, or delete your data. The attacker can also conduct other types of attacks, as described in the following sections.
A common denominator of most operating system and network security plans is password-based access control. This means your access rights to a computer and network resources are determined by who you are, that is, your user name and your password.
Older applications do not always protect identity information as it is passed through the network for validation. This might allow an eavesdropper to gain access to the network by posing as a valid user.
When an attacker finds a valid user account, the attacker has the same rights as the real user. Therefore, if the user has administrator-level rights, the attacker also can create accounts for subsequent access at a later time.
After gaining access to your network with a valid account, an attacker can do any of the following:
Obtain lists of valid user and computer names and network information.
Modify server and network configurations, including access controls and routing tables.
Modify, reroute, or delete your data.
Unlike a password-based attack, the denial-of-service attack prevents normal use of your computer or network by valid users.
After gaining access to your network, the attacker can do any of the following:
Randomize the attention of your internal Information Systems staff so that they do not see the intrusion immediately, which allows the attacker to make more attacks during the diversion.
Send invalid data to applications or network services, which causes abnormal termination or behavior of the applications or services.
Flood a computer or the entire network with traffic until a shutdown occurs because of the overload.
Block traffic, which results in a loss of access to network resources by authorized users.
As the name indicates, a man-in-the-middle attack occurs when someone between you and the person with whom you are communicating is actively monitoring, capturing, and controlling your communication transparently. For example, the attacker can re-route a data exchange. When computers are communicating at low levels of the network layer, the computers might not be able to determine with whom they are exchanging data.
Man-in-the-middle attacks are like someone assuming your identity in order to read your message. The person on the other end might believe it is you because the attacker might be actively replying as you to keep the exchange going and gain more information. This attack is capable of the same damage as an application-layer attack, described later in this section.
A key is a secret code or number necessary to interpret secured information. Although obtaining a key is a difficult and resource-intensive process for an attacker, it is possible. After an attacker obtains a key, that key is referred to as a compromised key.
An attacker uses the compromised key to gain access to a secured communication without the sender or receiver being aware of the attack.With the compromised key, the attacker can decrypt or modify data, and try to use the compromised key to compute additional keys, which might allow the attacker access to other secured communications.
A sniffer is an application or device that can read, monitor, and capture network data exchanges and read network packets. If the packets are not encrypted, a sniffer provides a full view of the data inside the packet. Even encapsulated (tunneled) packets can be broken open and read unless they are encrypted and the attacker does not have access to the key.
Using a sniffer, an attacker can do any of the following:
Analyze your network and gain information to eventually cause your network to crash or to become corrupted.
Read your communications.
An application-layer attack targets application servers by deliberately causing a fault in a server's operating system or applications. This results in the attacker gaining the ability to bypass normal access controls. The attacker takes advantage of this situation, gaining control of your application, system, or network, and can do any of the following:
Read, add, delete, or modify your data or operating system.
Introduce a virus program that uses your computers and software applications to copy viruses throughout your network.
Introduce a sniffer program to analyze your network and gain information that can eventually be used to crash or to corrupt your systems and network.
Abnormally terminate your data applications or operating systems.
Disable other security controls to enable future attacks.
Classes of attack might include passive monitoring of communications, active network attacks, close-in attacks, exploitation by insiders, and attacks through the service provider. Information systems and networks offer attractive targets and should be resistant to attack from the full range of threat agents, from hackers to nation-states. A system must be able to limit damage and recover rapidly when attacks occur.
There are five types of attack:
A passive attack monitors unencrypted traffic and looks for clear-text passwords and sensitive information that can be used in other types of attacks. Passive attacks include traffic analysis, monitoring of unprotected communications, decrypting weakly encrypted traffic, and capturing authentication information such as passwords. Passive interception of network operations enables adversaries to see upcoming actions. Passive attacks result in the disclosure of information or data files to an attacker without the consent or knowledge of the user.
In an active attack, the attacker tries to bypass or break into secured systems. This can be done through stealth, viruses, worms, or Trojan horses. Active attacks include attempts to circumvent or break protection features, to introduce malicious code, and to steal or modify information. These attacks are mounted against a network backbone, exploit information in transit, electronically penetrate an enclave, or attack an authorized remote user during an attempt to connect to an enclave. Active attacks result in the disclosure or dissemination of data files, DoS, or modification of data.
A distributed attack requires that the adversary introduce code, such as a Trojan horse or back-door program, to a “trusted” component or software that will later be distributed to many other companies and users Distribution attacks focus on the malicious modification of hardware or software at the factory or during distribution. These attacks introduce malicious code such as a back door to a product to gain unauthorized access to information or to a system function at a later date.
An insider attack involves someone from the inside, such as a disgruntled employee, attacking the network Insider attacks can be malicious or no malicious. Malicious insiders intentionally eavesdrop, steal, or damage information; use information in a fraudulent manner; or deny access to other authorized users. No malicious attacks typically result from carelessness, lack of knowledge, or intentional circumvention of security for such reasons as performing a task
A close-in attack involves someone attempting to get physically close to network components, data, and systems in order to learn more about a network Close-in attacks consist of regular individuals attaining close physical proximity to networks, systems, or facilities for the purpose of modifying, gathering, or denying access to information. Close physical proximity is achieved through surreptitious entry into the network, open access, or both.
One popular form of close in attack is social engineering in a social engineering attack, the attacker compromises the network or system through social interaction with a person, through an e-mail message or phone. Various tricks can be used by the individual to revealing information about the security of company. The information that the victim reveals to the hacker would most likely be used in a subsequent attack to gain unauthorized access to a system or network.
In phishing attack the hacker creates a fake web site that looks exactly like a popular site such as the SBI bank or paypal. The phishing part of the attack is that the hacker then sends an e-mail message trying to trick the user into clicking a link that leads to the fake site. When the user attempts to log on with their account information, the hacker records the username and password and then tries that information on the real site.
Hijack attack In a hijack attack, a hacker takes over a session between you and another individual and disconnects the other individual from the communication. You still believe that you are talking to the original party and may send private information to the hacker by accident.
Spoof attack In a spoof attack, the hacker modifies the source address of the packets he or she is sending so that they appear to be coming from someone else. This may be an attempt to bypass your firewall rules.
Buffer overflow A buffer overflow attack is when the attacker sends more data to an application than is expected. A buffer overflow attack usually results in the attacker gaining administrative access to the system in a ommand prompt or shell.
Exploit attack In this type of attack, the attacker knows of a security problem within an operating system or a piece of software and leverages that knowledge by exploiting the vulnerability.
Password attack An attacker tries to crack the passwords stored in a network account database or a password-protected file. There are three major types of password attacks: a dictionary attack, a brute-force attack, and a hybrid attack. A dictionary attack uses a word list file, which is a list of potential passwords. A brute-force attack is when the attacker tries every possible combination of characters.
By adopting the best technologies available today, the WiMAX, based on the IEEE 802.16e standard, provides strong support for authentication, key management, encryption and decryption, control and management of plain text protection and security protocol optimization. In WiMAX, most of security issues are addressed and handled in the MAC security sub-layer as described in the following figure:
Two main entities in WiMAX, including Base Station (BS) and Subscriber Station (SS), are protected by the following WiMAX security features:
Security association: A security association (SA) is a set of security information parameters that a BS and one or more of its client SSs share. Each SA has its own identifier (SAID) and also contains a cryptographic suite identifier (for selected algorithms), traffic encryption keys (TEKs) and initialization vectors.
Public key infrastructure: WiMAX uses the Privacy and Key Management Protocol (PKM) for secure key management, transfer and exchange between mobile stations. This protocol also authenticates an SS to a BS. The PKM protocol uses X.509 digital certificates, RSA (Rivest-Shamir-Adleman) public-key algorithm and a strong encryption algorithm (Advanced Encryption Standard – AES). The initial draft version of WiMAX uses PKMv1 which is a one-way authentication method and has a risk for Man-in-the-middle (MITM) attack. To deal with this issue, in the later version (802.16e), the PKMv2 was used to provide two-way authentication mechanism. The following figure provides an overview of public key infrastructure in WiMAX:
Device/User Authentication: Generally, WiMAX supports three types of authentication which are handled in the security sub-layer.
The first type is RSA-based authentication which applies X.509 certificates together with RSA encryption. The X.509 certificate is issued by the SS manufacturer and contains the SS’s public key (PK) and its MAC address. When requesting an Authorization Key (AK), the SS sends its digital certificate to the BS, the BS validates the certificate, and then uses the verified PK to encrypt an AK and pass it to the SS.
The second type is EAP (Extensive Authentication Protocol) based authentication in which the SS is authenticated by an X.509 certificate or by a unique operator-issued credential such as a SIM, USIM or even by user-name/password. The network operator can choose one of three types of EAP: EAP-AKA (Authentication and Key Agreement), EAP-TLS (Transport Layer Security) and EAP-TTLS MS-CHAP v2 (Tunneled Transport Layer Security with Microsoft Challenge-Handshake Authentication Protocol version 2).
The third type of authentication that the security sub-layer supports is the RSA-based authentication followed by EAP authentication.
Authorization: Following the authentication process is the authorization process in which SS requests for an AK and a SAID from BS by sending an Authorization Request message. This message contains SS's X.509 certificate, encryption algorithms and cryptographic ID. The BS then interacts with an AAA (Authentication, Authorization and Accounting) server to validate the request from the SS, and sends back an Authorization Reply which includes the AK encrypted with the SS’s public key, a lifetime key and an SAIS.
Data privacy and integrity: WiMAX adopts the AES algorithm for encryption. “The AES cipher is specified as a number of repetitions of transformation rounds that convert the input plain-text into the final output of cipher-text. Each round consists of several processing steps, including one that depends on the encryption key. A set of reverse rounds are applied to transform cipher-text back into the original plain-text using the same encryption key. Since DES is no more secure enough, AES is recommended in WiMAX with many supported modes: CCM-Mode and ECB-Mode (in IEEE 802.16-2004), CBC-Mode, CTR-Mode, AES-Key-Wrap.
WiMAX has been designed carefully with security concerns but it is still vulnerable to various attacks. The following section will present these security issues in WiMAX.
WiMAX has security vulnerabilities in both PHY and MAC layers, exposing to various classes of wireless attack including interception, fabrication, modification, and replay attacks. Some vulnerabilities of WiMAX originate from flaws of IEEE 802.16 on which WiMAX is based. A lot of problems and flaws have been fixed in the enhanced version but WiMAX still has some exposes.
In this section some possible threats or vulnerabilities will be reviewed and some solutions will be discussed.
Threats to the PHY layer
WiMAX security is implemented in the security sub-layer which is above the PHY layer. Therefore the PHY is unsecure and it is not protected from attacks targeting at the inherent vulnerability of wireless links such as jamming, scrambling or water torture attack. WiMAX supports mobility, thus it is more vulnerable to these attacks because the attackers do not need to reside in a fixed place and the monitoring solutions presented below will be more difficult.
Jamming is described by M. Barbeau as an attack “achieved by introducing a source of noise strong enough to significantly reduce the capacity of the channel”. Jamming can be either intentional or unintentional. It is not difficult to perform a jamming attack because necessary information and equipments are easy to acquire and there is even a book by Poisel which teaches jamming techniques.
Solutions: According to Michel Barbeau, we can prevent jamming attack by increasing the power of signals or by increasing the bandwidth of signals using spreading techniques such as frequency spread spectrum (FHSS) or direct sequence spread spectrum (DSS). Furthermore, since it is easy to detect jamming by using radio spectrum monitoring equipment and the sources of jamming are easy to be located by using radio direction finding tools, we can also ask help from law enforcement to stop the jammers.
Scrambling is a kind of jamming but only provoked for short intervals of time and targeted to specific WiMAX frames or parts of frames at the PHY layer. Attackers can selectively scramble control or management information in order to affect the normal operation of the network. Slots of data traffic belonging to the targeted SSs can be scrambled selectively, forcing them to retransmit. It is more difficult to perform an scrambling attack than to perform a jamming attack due to “the need, by the attacker, to interpret control information and to send noise during specific intervals”.
Solutions: Since scrambling is intermittent, it is more difficult to detect scrambling than jamming. Fortunately, we can use anomalies monitoring beyond performance norm (or criteria) to detect scrambling and scramblers .
In addition to threats from jamming, scrambling and water torture attacks, 802.16 is also vulnerable to other attacks such as forgery attacks in which an attacker with an adequate radio transmitter can write to a wireless channel. In mesh mode, 802.16 is also vulnerable to replay attacks in which an attacker resends valid frames that the attacker has intercepted in the middle of forwarding (relaying) process.
Solutions: WiMAX has fixed the security flaw of 802.16 by providing mutual authentication to defend these kinds of attacks.
There are a lot of defects or flaws in WiMAX security solutions at the MAC layer. The vulnerabilities with MAC management messages are presented first in section 3.2.1 and section 3.2.2. Then vulnerabilities in authentication mechanism and some specific attacks are discussed.
The initial network entry procedure is very important since it is the first gate to establish a connection to Mobile WiMAX by performing several steps including: initial Ranging process, SS Basic Capability (SSBC) negotiation, PKM authentication and registration process
The vulnerability of using Ranging Request-Response (RNG-REQ, RNG-RSP) messages: This message is used in the initial ranging process. The RNG-REQ message is sent by a SS trying to join a network to propose a request for transmission timing, power, frequency and burst profile information. Then, the BS responds by sending a RNG-RSP message to fine-tune the setting of transmission link. After that, the RNG-RSP can be used to change the uplink and downlink channel of the SS. There are several threats related to these messages. For instance, an attacker can intercept the RNG-REQ to change the most preferred burst profile of SS to the least effective one, thus downgrading the service. An attacker can also spoof or modify ranging messages to attack or interrupt regular network activities. This vulnerability can lead to a DoS attack which will be presented in details in 3.2.4 section of this report.
Other initial network entry vulnerability: T. Shon and W. Choi presented a more general vulnerability of initial network entry in. During the initial network entry process, many important physical parameters, performance factors, and security contexts between SS and BS, specifically the SBS negotiation parameters and PKM security contexts. Although the security schemes offered WiMAX include a message authentication scheme using HMAC/CMAC codes and traffic encryption scheme using AES based on PKMv2, these schemes are applied only to normal data traffic after initial network entry process. Subsequently, the parameters exchanged during this process are not securely protected, bringing a possible exposure to malicious users to attack.
Solution: T. Shon and W. Choi also proposed a solution to this vulnerability by using Diffie-Hellman key agreement scheme
In this approach, the Diffie-Hellman key agreement scheme will be used for SS and BS to generate a shared common key called “pre-TEK” separately and establish a secret communication channels in the initial ranging procedure. After that, the SBC security parameters and PKM security contexts can be exchanged securely.
T. Shon and W. Choi also reviewed a vulnerability in access network security in WiMAX. In order to accommodate the requirements of WiMAX End-to-End Network Systems Architecture for mobile WiMAX network, the WiMAX forum defined network Reference Model (NRM) which consists of the following entities: Subscriber Station (SS), Access Service Network (ASN), and Connectivity Service Network (CSN). ASN consists of at least one BS and one ASN Gateway (ASN/GW) forming a complete set of network functions necessary to provide radio access to mobile subscribers. CSN consists of AAA Proxy/Server, Policy, Billing, and Roaming Entities forming a set of network functions to provide IP connectivity services to subscribers. This AAA-architecture based model is illustrated in the following figure.
T. Shon and W. Choi divided the model into three insecure domains and one secure domain . The only secure domain covered by encryption and authentication schemes in 802.16 standard is the data communications between SS and BS. The initial network entry which is examined in the 3b section belongs to domain A. Domain B and C are considered insecure because the Network Working Group in WiMAX forum just assumes that domain B is in a trusted network without proposing any protection and just suggests a possibility of applying an IPSec tunnel between ASN and AAA in domain C.
Solutions: T. Shon and W. Choi proposed a countermeasure for this problem by using a simple and efficient key exchange method based on PKI. Their method is described in the following figure:
In this approach, all network devices have their certificate and a certificate chain for verification. The PKI structure is used as a method to obtain correspondent’s public keys and verify the certificates, thus enabling entities to create a shared secret key for establishing a secure connection.
Many serious threats also arises from the WiMAX’s authentication scheme in which masquerading and attacks on the authentication protocol of PKM are the most considerable.
Masquerade attack is a type of attack in which one system assumes the identity of another. WiMAX supports unilateral device level authentication which is a RSA/X.509 certificate based authentication. The certificate can be programmed in a device by the manufacturer. Therefore sniffing and spoofing can make a masquerade attack possible. Specifically, there are two techniques to perform this attack: identity theft and rogue BS attack.
An attacker reprogram a device with the hardware address of another device. The address can be stolen by interfering the management messages.
Rogue BS attack:
SS can be compromised by a forged BS which imitates a legitimate BS. The rogue BS makes the SSs believing that they are connected to the legitimate BS, thus it can intercept SSs’ whole information. In IEEE 802.16 using PKMv1, the lack of mutual authentication prevents confirming the authentication of BS and makes Man-In-The-Middle (MITM) attack through rogue BS possible by sniffing Auth-related message from SS. However, it is difficult to successfully perform this kind of attack in WiMAX which supports mutual authentication by using PKMv2.
Attacks on the authentication protocols of basic PKM in 802.16 and its later version-PKMv2:
By adopting new version of PKM, WiMAX fixes many flaws in PKMv1 such as vulnerability to MITM due to the lack of mutual authentication. However, the newly proposed PKMv2 has been found to be also vulnerable to new attacks .
Attacks on basic PKM authentication protocol:
Attacker can intercept and save the messages sent by a legal SS and then perform a replay attack against the BS. The SS also might face with this kind of attack. In the worse case, since mutual authentication is not supported in basic PKM, BS is not authenticated. Therefore malicious BS can perform a MITM attack by making its own Auth-Reply message and gain the control of the communication of victim SS. S. Xu et. al. concluded that Basic PKM has many flaws such that it provides almost no guarantees to SS about the AK. These problems have been fixed in the Intel Nonce version of PKM.
Attacks on Intel Nonce Version PKM: In this version, nonce is a possible alternative to timestamp in authentication protocol. This approach does not protect a BS from a replay attack.
Attacks on PKMv2:
This version provides a three-way authentication with a confirmation message from SS to BS. There are two possible attacks as follows. First, a replay attack can be performed if there is no signature by SS. Second, even with the signature form SS, an interleaving attack is still possible.
Some serious attacks can exploit vulnerabilities in many aspect of the MAC layers. Two of the most destructive attacks can be MITM and DoS attacks.
Man in the middle attack:
Although WiMAX can prevent MITM attack through rogue BS by using PKMv2, it is still vulnerable to MITM attack. This possibility is due to the vulnerabilities in initial network entry procedure which is already presented in part 3.2.2 of this report. In 3.2.2, it is known that WiMAX standard does not provide any security mechanism for the SSBC negotiation parameters. Tao Han et. al. in shows that through intercepting and capturing message in the SSBC negotiation procedure, an attacker can imitate a legitimate SS and send tamped SSBC response message to the BS while interrupting the communication between them. The spoof message would inform the BS that the SS only supports low security capabilities or has no security capability. If the BS still accepts, then the communication between the SS and the BS will not have a strong protection. Under these circumstances, the attacker is able to wiretap and tamper all the information transmitted.
Tao Han et. al. also proposed their solution to this kind of attack which they called “SINEP”. Their method is based on Diffie-Hellman (DH) key exchange protocol. This approach is very similar to that by T. Shon and W. Choi in .
Denial of Service attack:
Comprehensive surveys show that there are many vulnerabilities exposing IEEE 802.16e networks to DoS attacks such as unprotected network entry, unencrypted management communication, unprotected management frame, weak key sharing mechanism in multicast and broadcast operations, and Reset-Command message).
Some of noticeable DoS attacks may include the following:
DoS attacks based on Ranging Request/Response (RNG-REG/RNG-RSP) messages:
An attacker can forge a RNG-RSP message to minimize the power level of SS to make SS hardly transmit to BS, thus triggering initial ranging procedure repeatedly. An attacker can also perform a water torture DoS by maximizing the power level of SS, effectively draining the SS’s battery.
DoS attacks based on Mobile Neighbor Advertisement (MOB_NBR_ADV) message:
MOB_NBR_ADV message is sent from serving BS to publicize the characteristics of neightbor base stations to SSs searching for possible handovers. This message is not authenticated. Thus it can be forged by an attacker in order to prevent the SSs from efficient handovers downgrading the performance or even denying the legitimate service.
DoS attacks based on Fast Power Control (FPC) message:
FPC message is sent from BS to ask a SS to adjust its transmission power. This is also one of the management messages which are not protected. An attacker can intercept and use FPC message to prevent a SS from correctly adjusting transmission power and communicating with the BS. He can also use this message to perform a water torture DoS attack to drain the SS’s battery.
DoS attacks based on Authorization-invalid (Auth-invalid) message:
The Auth-invalid is sent from a BS to a SS when AK shared between BS and SS expires or BS is unable to verify the HMAC/CMAC properly. This message is not protected by HMAC and it has PKM identifier equal to zero. Thus, it can be used as DoS tool to invalidate legitimate SS.
DoS attacks based on Reset Command (RES-CMD) message:
This message is sent to request a SS to reinitialize its MAC state machine, allowing a BS to reset a non-responsive or malfunction SS. This message is protected by HMAC but is still potential to be used to perform a DoS attacks.
In order to prevent DoS attacks, we first need to fix the vulnerabilities in the initial network entry. This work is discussed in section 3.2.1 of this report. Sheraz Naseer et. al also suggest that the authentication mechanism should be extended to as many management frame as possible. They also suggest using digital signatures as an authentication method