A Distributed Denial of Service (DDoS) attack is an attempt to make an online service or a website unavailable by overloading it with huge floods of traffic generated from multiple sources.
Unlike a Denial of Service (DoS) attack, in which one computer and one Internet connection is used to flood a targeted resource with packets, a DDoS attack uses many computers and many Internet connections, often distributed globally in what is referred to as a botnet.
A large scale volumetric DDoS attack can generate a traffic measured in tens of Gigabits (and even hundreds of Gigabits) per second. We are sure your normal network will not be able to handle such traffic.
What are Botnets?
Attackers build a network of hacked machines which are known as botnets, by spreading malicious piece of code through emails, websites, and social media. Once these computers are infected, they can be controlled remotely, without their owners' knowledge, and used like an army to launch an attack against any target.
A DDoS flood can be generated in multiple ways. For example −
Botnets can be used for sending more number of connection requests than a server can handle at a time.
Attackers can have computers send a victim resource huge amounts of random data to use up the target's bandwidth.
Due to the distributed nature of these machines, they can be used to generate distributed high traffic which may be difficult to handle. It finally results in a complete blockage of a service.
Types of DDoS Attacks
DDoS attacks can be broadly categorized into three categories −
- Volume-based Attacks
- Protocol Attacks
- Application Layer Attacks
Volume-Based Attacks
Volume-based attacks include TCP floods, UDP floods, ICMP floods, and other spoofedpacket floods. These are also called Layer 3 & 4 Attacks. Here, an attacker tries to saturate the bandwidth of the target site. The attack magnitude is measured in Bits per Second (bps).
UDP Flood − A UDP flood is used to flood random ports on a remote host with numerous UDP packets, more specifically port number 53. Specialized firewalls can be used to filter out or block malicious UDP packets.
ICMP Flood − This is similar to UDP flood and used to flood a remote host with numerous ICMP Echo Requests. This type of attack can consume both outgoing and incoming bandwidth and a high volume of ping requests will result in overall system slowdown.
HTTP Flood − The attacker sends HTTP GET and POST requests to a targeted web server in a large volume which cannot be handled by the server and leads to denial of additional connections from legitimate clients.
Amplification Attack − The attacker makes a request that generates a large response which includes DNS requests for large TXT records and HTTP GET requests for large files like images, PDFs, or any other data files.
Protocol Attacks
Protocol attacks include SYN floods, Ping of Death, fragmented packet attacks, Smurf DDoS, etc. This type of attack consumes actual server resources and other resources like firewalls and load balancers. The attack magnitude is measured in Packets per Second.
DNS Flood − DNS floods are used for attacking both the infrastructure and a DNS application to overwhelm a target system and consume all its available network bandwidth.
SYN Flood − The attacker sends TCP connection requests faster than the targeted machine can process them, causing network saturation. Administrators can tweak TCP stacks to mitigate the effect of SYN floods. To reduce the effect of SYN floods, you can reduce the timeout until a stack frees memory allocated to a connection, or selectively dropping incoming connections using a firewall or iptables.
Ping of Death − The attacker sends malformed or oversized packets using a simple ping command. IP allows sending 65,535 bytes packets but sending a ping packet larger than 65,535 bytes violates the Internet Protocol and could cause memory overflow on the target system and finally crash the system. To avoid Ping of Death attacks and its variants, many sites block ICMP ping messages altogether at their firewalls.
Application Layer Attacks
Application Layer Attacks include Slowloris, Zero-day DDoS attacks, DDoS attacks that target Apache, Windows or OpenBSD vulnerabilities and more. Here the goal is to crash the web server. The attack magnitude is measured in Requests per Second.
Application Attack − This is also called Layer 7 Attack, where the attacker makes excessive log-in, database-lookup, or search requests to overload the application. It is really difficult to detect Layer 7 attacks because they resemble legitimate website traffic.
Slowloris − The attacker sends huge number of HTTP headers to a targeted web server, but never completes a request. The targeted server keeps each of these false connections open and eventually overflows the maximum concurrent connection pool, and leads to denial of additional connections from legitimate clients.
NTP Amplification − The attacker exploits publically-accessible Network Time Protocol (NTP) servers to overwhelm the targeted server with User Datagram Protocol (UDP) traffic.
Zero-day DDoS Attacks − A zero-day vulnerability is a system or application flaw previously unknown to the vendor, and has not been fixed or patched. These are new type of attacks coming into existence day by day, for example, exploiting vulnerabilities for which no patch has yet been released.
How to Fix a DDoS Attack
There are quite a few DDoS protection options which you can apply depending on the type of DDoS attack.
Your DDoS protection starts from identifying and closing all the possible OS and application level vulnerabilities in your system, closing all the possible ports, removing unnecessary access from the system and hiding your server behind a proxy or CDN system.
If you see a low magnitude of the DDoS, then you can find many firewall-based solutions which can help you in filtering out DDoS based traffic. But if you have high volume of DDoS attack like in gigabits or even more, then you should take the help of a DDoS protection service provider that offers a more holistic, proactive and genuine approach.
You must be careful while approaching and selecting a DDoS protection service provider. There are number of service providers who want to take advantage of your situation. If you inform them that you are under DDoS attack, then they will start offering you a variety of services at unreasonably high costs.
We can suggest you a simple and working solution which starts with a search for a good DNS solution provider who is flexible enough to configure A and CNAME records for your website. Second, you will need a good CDN provider that can handle big DDoS traffic and provide you DDoS protection service as a part of their CDN package.
Assume your server IP address is AAA.BBB.CCC.DDD. Then you should do the following DNS configuration −
Create a A Record in DNS zone file as shown below with a DNS identifier, for example, ARECORDID and keep it secret from the outside world.
Now ask your CDN provider to link the created DNS identifier with a URL, something like cdn.someotherid.domain.com.
You will use the CDN URL cdn.someotherid.domain.com to create two CNAME records, the first one to point to www and the second record to point to @ as shown below.
You can take the help from your system administrator to understand these points and configure your DNS and CDN appropriately. Finally, you will have the following configuration at your DNS.
Now, let the CDN provider handle all type of DDoS attacks and your system will remain safe. But here the condition is that you should not disclose your system's IP address or A record identifier to anyone; else direct attacks will start again.
Quick Fix
DDoS attacks have become more common than ever before, and unfortunately, there is no quick fix for this problem. However, if your system is under a DDoS attack, then don’t panic and start looking into the matter step by step.
Cross Site Scripting
Cross-site scripting (XSS) is a code injection attack that allows an attacker to execute malicious JavaScript in another user's browser.
The attacker does not directly target his victim. Instead, he exploits a vulnerability in a website that the victim visits, in order to get the website to deliver the malicious JavaScript for him. To the victim's browser, the malicious JavaScript appears to be a legitimate part of the website, and the website has thus acted as an unintentional accomplice to the attacker. These attacks can be carried out using HTML, JavaScript, VBScript, ActiveX, Flash, but the most used XSS is malicious JavaScript.
These attacks also can gather data from account hijacking, changing of user settings, cookie theft/poisoning, or false advertising and create DoS attacks.
Example
Let’s take an example to understand how it works. We have a vulnerable webpage that we got by the metasploitable machine. Now we will test the field that is highlighted in red arrow for XSS.
First of all, we make a simple alert script
<script> alert(‘I am Vulnerable’)</script>
It will produce the following output −
Types of XSS Attacks
XSS attacks are often divided into three types −
Persistent XSS, where the malicious string originates from the website's database.
Reflected XSS, where the malicious string originates from the victim's request.
DOM-based XSS, where the vulnerability is in the client-side code rather than the server-side code.
Generally, cross-site scripting is found by vulnerability scanners so that you don’t have to do all the manual job by putting a JavaScript on it like
<script> alert('XSS')</script>
Burp Suite and acunetix are considered as the best vulnerability scanners.
Quick Tip
To prevent XSS attacks, keep the following points in mind −
Check and validate all the form fields like hidden forms, headers, cookies, query strings.
Implement a stringent security policy. Set character limitation in the input fields.
SQL Injection
SQL injection is a set of SQL commands that are placed in a URL string or in data structures in order to retrieve a response that we want from the databases that are connected with the web applications. This type of attacks generally takes place on webpages developed using PHP or ASP.NET.
An SQL injection attack can be done with the following intentions −
To dump the whole database of a system,
To modify the content of the databases, or
To perform different queries that are not allowed by the application.
This type of attack works when the applications don’t validate the inputs properly, before passing them to an SQL statement. Injections are normally placed put in address bars, search fields, or data fields.
The easiest way to detect if a web application is vulnerable to an SQL injection attack is to use the " ‘ " character in a string and see if you get any error.
Example 1
Let’s try to understand this concept using a few examples. As shown in the following screenshot, we have used a " ‘ " character in the Name field.
Now, click the Login button. It should produce the following response −
It means that the “Name” field is vulnerable to SQL injection.
Example 2
We have this URL − http://10.10.10.101/mutillidae/index.php?page=site-footer-xssdiscussion.php
And we want to test the variable “page” but observe how we have injected a " ‘ " character in the string URL.
When we press Enter, it will produce the following result which is with errors.
SQLMAP
SQLMAP is one of the best tools available to detect SQL injections. It can be downloaded from http://sqlmap.org/
It comes pre-compiled in the Kali distribution. You can locate it at − Applications → Database Assessment → Sqlmap.
After opening SQLMAP, we go to the page that we have the SQL injection and then get the header request. From the header, we run the following command in SQL −
./sqlmap.py --headers="User-Agent: Mozilla/5.0 (X11; Ubuntu; Linux i686; rv:25.0)Gecko/20100101 Firefox/25.0" --cookie="security=low;PHPSESSID=oikbs8qcic2omf5gnd09kihsm7" -u 'http://localhost/dvwa/vulnerabilities/sqli_blind/?id=1&Submit=Submit#' -level=5 risk=3 -p id --suffix="-BR" -v3
The SQLMAP will test all the variables and the result will show that the parameter “id” is vulnerable, as shown in the following screenshot.
SQLNinja
SQLNinja is another SQL injection tool that is available in Kali distribution.
JSQL Injection
JSQL Injection is in Java and it makes automated SQL injections.
Quick Tips
To prevent your web application from SQL injection attacks, you should keep the following points in mind −
Unchecked user-input to database should not be allowed to pass through the application GUI.
Every variable that passes into the application should be sanitized and validated.
The user input which is passed into the database should be quoted.
Pen Testing
Penetration Testing is a method that many companies follow in order to minimize their security breaches. This is a controlled way of hiring a professional who will try to hack your system and show you the loopholes that you should fix.
Before doing a penetration test, it is mandatory to have an agreement that will explicitly mention the following parameters −
what will be the time of penetration test,
where will be the IP source of the attack, and
what will be the penetration fields of the system.
Penetration testing is conducted by professional ethical hackers who mainly use commercial, open-source tools, automate tools and manual checks. There are no restrictions; the most important objective here is to uncover as many security flaws as possible.
Types of Penetration Testing
We have five types of penetration testing −
Black Box − Here, the ethical hacker doesn’t have any information regarding the infrastructure or the network of the organization that he is trying to penetrate. In black-box penetration testing, the hacker tries to find the information by his own means.
Grey Box − It is a type of penetration testing where the ethical hacker has a partial knowledge of the infrastructure, like its domain name server.
White Box − In white-box penetration testing, the ethical hacker is provided with all the necessary information about the infrastructure and the network of the organization that he needs to penetrate.
External Penetration Testing − This type of penetration testing mainly focuses on network infrastructure or servers and their software operating under the infrastructure. In this case, the ethical hacker tries the attack using public networks through the Internet. The hacker attempts to hack the company infrastructure by attacking their webpages, webservers, public DNS servers, etc.
Internal Penetration Testing − In this type of penetration testing, the ethical hacker is inside the network of the company and conducts his tests from there.
Penetration testing can also cause problems such as system malfunctioning, system crashing, or data loss. Therefore, a company should take calculated risks before going ahead with penetration testing. The risk is calculated as follows and it is a management risk.
RISK = Threat × Vulnerability
Example
You have an online e-commerce website that is in production. You want to do a penetration testing before making it live. Here, you have to weigh the pros and cons first. If you go ahead with penetration testing, it might cause interruption of service. On the contrary, if you do not wish to perform a penetration testing, then you can run the risk of having an unpatched vulnerability that will remain as a threat all the time.
Before doing a penetration test, it is recommended that you put down the scope of the project in writing. You should be clear about what is going to be tested. For example −
Your company has a VPN or any other remote access techniques and you want to test that particular point.
Your application has webservers with databases, so you might want to get it tested for SQL injection attacks which is one of the most crucial tests on a webserver. In addition, you can check if your webserver is immune to DoS attacks.
Quick Tips
Before going ahead with a penetration test, you should keep the following points in mind −
First understand your requirements and evaluate all the risks.
Hire a certified person to conduct penetration test because they are trained to apply all the possible methods and techniques to uncover possible loopholes in a network or web application.
Always sign an agreement before doing a penetration test.
Thankyou very much today I completed last part of Hacking.....
