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Hello, aspiring ethical hackers. In this blogpost, you will learn about most common firewall bypass techniques used by hackers and pen testers in real world. In our previous blogposts on Firewalls and IDS and IPS, you learnt in detail what are firewalls, Intrusion Detection System (IDS), Intrusion Prevention System (IPS), types of Firewalls, IDS and IPS and various techniques used by them to do what they do best. Please read them first to better understand how firewall bypass techniques described below work.

Why do hackers and pen testers bypass Firewalls and IDS and IPS?

Before you learn about different techniques hackers and pen testers use to bypass firewalls, IDS ad IPS, you need to understand why it is important to bypass them. In real-world networks of organizations, firewall, IDS and IPS are the most common devices or software that are employed by organizations to keep their network secure. So, in order to reach the actual network, a penetration tester or hacker has to bypass the firewalls. The result of a successful pen test depends on the bypass techniques they use.

Common firewall bypass techniques

Pen tester or hackers employ various techniques to bypass firewalls, IPS and IDS. They are,

1. Spoofing the IP address.
2. Proxies.
3. Fragmenting packets.
4. Source routing.
5. Source port manipulation.

Let’s learn about each of these techniques in detail.

1. Spoofing the IP address:

If firewalls detect malicious traffic coming from a particular IP address or IP range, they just block the IP address to prevent malicious activity. This is one of the simplest functions of a Firewall or IPS. However, hackers or pen testers can bypass this by spoofing the source IP address. Learn more about IP address spoofing.

2. Proxies:

Hackers in real world and pen testers always hack their targets routing through another machine or computer. This is known as proxy. Hackers do this for covering tracks and do this to hide their activity. They also do this to bypass firewalls especially when the IP address is blocked by the firewall. They can also use proxy server for this purpose.

3. Packet fragmentation:

Data through network is transferred in the form of network packets. Each packet contains all the information needed for data transmission like the source IP address, destination IP address, source port and destination port etc. Firewalls and IDS analyses these packets for information. Each packet can be fragmented into small chunks and then transmitted. Fragmented packets are reassembled at the target machine. Reassembling the fragmented packets take lot of time and consume lot of resources. Most Firewalls and IPS are configured to ignore packets that are fragmented.

4. Source routing:

When a network packet is sent from the source system to the destination system, it hops through a number of devices before it reaches the destination machine. If a firewall or IDS is present in the route taken by the packet, it is blocked. So, hackers try to send this packet through a different route that doesn’t have a firewall or IDS. This is known as source routing.

5. Source port manipulation:

Firewalls allow traffic through some ports by default, say for example, HTTP port. If the source port is manipulated in the network packet, then it can bypass the firewall.

Hello, aspiring ethical hackers. Payloads play a very important role in ethical hacking. In this blogpost, you will learn everything about Metasploit payloads beginning from what is a payload, how many types of payloads are there and various functions of payloads etc.

What is a payload?

A payload in cyber security is a piece of code that is executed after successfully running an exploit to take advantage of a vulnerability. When a Proof Of Concept (POC) for a vulnerability is disclosed, this allows most hackers around the world to execute their chosen payloads. This payload can be anything from malware, reverse shell, RAT, ransomware etc or their own custom payload.

For example, ms08_067 vulnerability was exploited in real-world to deploy Conficker worm, but while pen testing, a meterpreter payload is used most probably.

Types of Metasploit payloads

Payloads in Metasploit can be classified into three types based on their function. They are.

1. Staged payloads or stagers.
2. Stageless or Non-staged (Inline) payloads or Single payloads.
3. Stages

1. Single or Stageless / Non-staged or Inline payload:

A single payload s self-contained as it contains in itself all the code required to do what it does. This is one of the easiest payloads to create but its size is a bit large. This may increase suspicions.

2. Stager payload:

Stager payloads also known as stagers set the stage for another payload. Their purpose is to establish a network connection between the target system and attacker system.

3. Stages:

This is the payload that is downloaded by stager payload.

Hello, aspiring ethical hackers. In this blogpost, you will learn about various Data-Link Layer attacks (various hacking attacks that take place on the Data-Link layer).

The Data-link layer is the second layer of the seven-layer OSI model. This layer is the protocol layer that transports data between network nodes in a wide Area Network or nodes in the same Local Area Network (LAN). It is responsible for ensuring and confirming that the bits and bytes received are similar to the bits and bytes being transmitted. In this layer, data is transferred in frames and communication takes place using MAC addresses instead of IP addresses. The attacks in the Data-link Layer take place in a LAN.

What is a Network Hub?

A network hub is a hardware device that connects multiple devices to a network and allows them to communicate with each other and share resources.

Just imagine, you have a router with 5 LAN ports. Using LAN cables, you can connect 5 devices to this router. Now, what if you want to connect 10 devices to the same network. This is where the use of network hub comes. You can connect a network Hub to one of the ports of a router. Let’s say this network hub has 10 LAN ports. So you can connect 10 computer devices to the same network. Similarly you can connect Network Hub to all ports of the routers to extend the network.

The only disadvantage with Hub is that it sends traffic intended to be between two machines to all the devices of the network. Other than consuming bandwidth, it also poses security threats like sniffing.

For example, let’s say someone from machine “B” in a network is logged into telnet server on machine “A”. You have seen in our packet sniffing blogpost that in telnet protocol, data is transferred in plain text format. So in a Hub based network, the network traffic intended to be between “A” and “B” will even go to another machine in the network “C”. If a hacker is on machine “C” he can view the telnet credentials by sniffing.

What is a Network Switch?

The above reasons are why, network Hubs have been replaced by Network Switches. A Switch, similar to a Network Hub in a hardware device that connects all the device of a network. The only difference in switch sends the traffic to the intended device instead of all the devices in the network

What is a MAC address?

Just now, you have read that communication between devices in a LAN takes place using MAC addresses. But what is a MAC address? Every computing device on Internet (Desktop, Laptop and Mobiles etc) has a Network Interface Card (NIC). This Network Interface Card (NIC) is a hardware circuit in the computing devices that enables the devices to be able to connect to a network.

Each NIC is given a unique hardware address that is also popularly known as a Media Access Control (MAC) address. A MAC addresses is a 48-bit number consisting of six groups of two hexadecimal digits. To learn how MAC addresses are assigned to devices and how to find MAC address of your device, you can read this blogpost.

Types of Data-Link layer attacks

Since now you have understood how Data-Link layer works and what is a MAC address, let’s learn about various Data-link layer attacks.

1. MAC spoofing
2. MAC flooding
3. ARP spoofing or poisoning
4. DNS spoofing
5. DHCP starvation

Let’s learn about each attack in detail.

1. MAC spoofing:

Although every computing device has its unique MAC address, it can be spoofed. Normally, when a MAC address of a device (say A) is spoofed to that of another device (say B) all the traffic that is intended to move toward device B goes to device A and the attacker can view all the traffic belonging to device B.

2. MAC flooding:

You have just now learnt about what is a Hub and what is a Switch and the differences between a Hub and Switch. You also learnt about CAM table or ARP table. In a MAC flooding attack, the CAM table is bombarded with a number of fake MAC addresses disabling the Switch’s ability to detect which MAC address belongs to which port.

To overcome this problem, a network Switch uses its broadcast address to transmit frames to the intended destination. In typical sense, the network switch here behaves like a Hub and you know about the dangers of using a Hub. A hacker already in the network can monitor the network traffic he wants via packet sniffing.

3. ARP spoofing and poisoning:

In this type of attack, the attacker sends fake ARP packets to the network from the attacker-controlled system (System A). Here, the attacker-controlled system acts as the gateway. This leads to all other devices querying the attacker-controlled system resulting in the attackers using packet sniffing again to sniff on traffic.

4. DNS spoofing:

This attack requires ARP spoofing to work. In this type of attack, attacker responds to DNS queries of the target system instead of the legitimate DNS server.

Hello, aspiring ethical hackers. This blogpost is a beginner guide to IDS (Intrusion Detection System) and IPS (Intrusion Preventions System). IDS and IPS are two of the security technologies used for securing the network of any organization from hackers.

What is an IDS and what is an IPS?

Intrusion Detection system (IDS) is an appliance or software that detects any malicious activity on the network and reports it. Intrusion Prevention System (IPS) on the other hand acts just like Intrusion Detection System but, unlike it doesn’t just make a report but tries to prevent its occurrence. This malicious activity can be anything like modification of system or important files, suspicious network traffic and execution of some files etc. Both Intrusion Detection System (IDS) and Intrusion Prevention System (IPS) are useful in enhancing the security of the network.

Based on the mode of operation, Intrusion Detection System and Intrusion Prevention System can be classified into two types. They are, 1) Host based (Software) 2) Network based (Hardware).

1. Host based Intrusion Detection and Prevention Systems: They work by detecting or preventing threats on a single system.
2. Network based Intrusion Detection and Prevention Systems: These are most probably a hardware appliance that detects or prevents threats on the entire network.

Types of IPS and IDS

Based on the techniques they use to identify and prevent threats, Intrusion Detection Systems and Intrusion Prevention Systems can be classified into two types. They are,

1. Signature-based :

This type of Intrusion Prevention Systems and Intrusion Detection Systems detect threats by comparing actions with predefined signatures. For example, If action of an executable matches with a pre-defined signature of an IDS or IPS, it is classified as a threat.

2. Anomaly based:

Anomaly based Intrusion Detection Systems and Intrusion Prevention Systems detect threats by observing the behavior of the assumed threat. If the IDS and IPS see any different behavior than that is considered to be normal, it classifies it as a threat. For example, if a program being installed is trying to alter system files, this can be considered as an anomaly.

Hello, aspiring ethical hackers. In this blogpost, you will learn about covering tracks which is the last of the 5 phases of ethical hacking.

What is Covering tracks?

Covering tracks or clearing tracks is the phase of ethical hacking in which a hacker tries to erase all the evidence on the target system that can lead back to the hacker. For covering tracks, hackers perform various actions. They are,

1. Uninstalling executables and scripts:

Hackers install many scripts and executables on the target system as part of their hacking attack. These scripts may help hackers cracking passwords, privilege escalation, maintaining access etc. Detection of these scripts and executables on the target system can lead the investigators to the hacker. So, hackers uninstall or delete any scripts or executables they have used in carrying the hacking attack.

2. Clearing logs:

Every operating system has its own logs that record different operational activities being performed on the operating system. They also record any actions performed by hackers. When an incident investigator observes these logs, he can easily deduce what the hacker did on the target system. To prevent this, hackers clear these logs to hide whatever they did on the target system.

3. Timestamping files:

Every file on the operating system has a time stamp which reveals information about the file like the date of its creation, last modified time etc. Hackers change this timestamp of the files appropriately to prevent detection of the modifications they made to files inadvertently while hacking.

4. Modifying registry values:

The Windows Registry in the Windows operating system is a hierarchical database that contains information, settings, options, and other values for programs and hardware installed on the Windows operating system. Changes made to some program can also be detected by viewing this registry. So, hackers also modify these registry values to hide their malicious activity.