The Mega Guide to Information Security Interview Questions.

by Shankar Damodaran — on  ,  ,  , 


Almost 16 questions and still counting, I’ve been contributing to this post on a regular basis. This is beneficial for anyone who wants to recall their knowledge on information security topics. This can also be used as a Guide to prepare for Information Security Openings. The Information Security topics were intentionally shuffled to achieve robustness to the reader.

1. What is a Repudiation Attack?

An attacker can prove a vulnerability exists in an application without actually denying the attack made by him/her. This example can be compared with “Google Hacking”. The attacker would have used Google Dork to find a weakness in the website without directly penetrating it. One more classic example would be the same website may have an information disclosure vulnerability in one of their pages if the error wasn’t handled properly. Repudiation Attacks may also be termed as “Passive Attacks”.

2. What is a False Positive and a False Negative?

False Positive: An automated scanner scans a website and it shows the website is prone to some attack (say, SQLi, CSRF, etc), which actually isn’t. The site is safe.
False Negative: An automated scanner scans a website and it shows the website is safe from attacks (say, SQLi, CSRF, etc), which actually isn’t. The site isn't safe.

3. What is the key difference between Penetration Testing and Vulnerability Assessment?

Penetration Testing is a process of breaking into the system and trying to gain the maximum privilege on the network. The ultimatum here is to get to the deepest level inside a network. This process is more similar to how an intruder would penetrate except there will be no damage caused. The steps has to be properly documented on how the actions were performed to gain the highest privilege.
Vulnerability Assessment is a process of listing out all weaknesses in the machine (either by using a tool/manual ways) that is being assessed and list out the vulnerabilities in the highest order of risk. This process stops with this and does not further delve as of Penetration Testing.

4. How to define CSRF attack in an easier way?

Cross Site Request Forgery or CSRF is a vulnerability in a website that allows an attacker to trick an end-user(victim in this case) into performing malicious operations without their knowledge in the background.

5. Which is more important to fix “Threat” or “Vulnerability”?

Threats can be classified as “Inside Intruder”, “Natural Disasters”, etc whereas Vulnerabilities can be classified as weaknesses such as “SQLi”, “XSS”, “CSRF”, “Non Availability of Bunkers for protection against natural disasters”, etc. A Threat must make use a Vulnerability to exploit or create damage to the data. So it is important to fix vulnerabilities first than to focus on threats. Sometimes this can also be counter-intuitive, an insider working for an organization may pass vital information (eg: admin credentials) to an outside intruder. The outsider can directly login to the application with the credentials and can cause damage to the data (in this case, the outsider did not make use of any vulnerability to exploit the application).
Hence, there is no prefect answer that can be provided to the above question.

6. How do you stop Brute-Force Attacks?

  • Adding a CAPTCHA functionality to the login forms.
  • Enforce account lockout mechanism for a maximum of three to four wrong attempts.
  • Fastest fix for a temporary period would be blocking the particular ip address that is making the brute force attempts.
  • Authentication Delays.

7. What’s the difference between an “Exploit” and a “Payload”?

An exploit is the medium in the which the payload is contained.Both represent a “piece of code”, but a payload does contain the actual attack whereas an exploit can be termed as a “carrier”. To make the explanation more clear and precise, take a rifle/gun for an instance. The “Gun” is the exploit whereas the “bullet” is the actual payload.

8. Why is encryption used for confidentiality instead of encoding?

Encryption and Encoding uses publicly available algorithms. Encoding is not used for confidentiality purposes since the content that has been encoded using algorithms like (Base64, UTF, etc) can be reversed with their available algorithms and there is no secret key involved. In an encryption scheme like an (AES, 3-DES, etc) they have corresponding encryption and decryption algorithms which involves a common secret key.

9. Which type of scan is performed by NMAP through default settings?

Nmap uses a “SYN” scan by default unless we specify anything. -sS will be the default setting for Nmap. SYN scans are faster as they do not create the Three-way-handshake (SYN-><-SYN-ACK->ACK). Instead of the ACK, the SYN scan sends an RST packet, thus the connection will be closed and there won’t be any chances for DoS condition. SYN scans were previously called as “Stealth Scans” as the logging devices do not record activities since a three-way-handshake wasn’t established. Nowadays, the devices do record activity of SYN scans too, so it is not fair to call it as a “Stealth Scan” anymore.

10. On which port does Nessus run?

8834. Nessus can be accessed through any browser by accessing

11.How do you differentiate “Bind Payloads” and “Reverse Payloads”?

Bind Payloads are a piece of code which is sent by the attacker to the target machine. The exploit then runs on the machine as a process on a certain port say 4444 passively. The attacker can connect to this target by establishing connection to this particular port.
Reverse Payloads are also a piece of code that is sent by attacker and in the background the attacker runs another process that keeps listening to the port say 4444., when this exploit is executed, the target machine immediately sends a connection to the attacker machine that is passively listening on the background.

12. What is a “Promiscuous Mode and Non-Promiscuous Mode” while capturing packets with a packet sniffer?

In a “Promiscuous Mode” whichever packets that reaches the Network Interface Card is compelled to accept eventhough it was not intended for that NIC’s particular MAC address. That’s one of the reason we mostly sniff traffic using this mode. In a “Non-Promiscuous Mode”, the packets are processed only if they are intended for that NIC’s MAC address, others are discarded as it is.

13. What is an Open Redirect?

It resides in one of the OWASP Top 10, This happens in a site which does not properly validate parameters that happens during a redirect. For instance; Consider this URL What an attacker does is that he could use this opportunity to redirect the logged in users to his/her site by crafting a URL like this.

14. How would you rate or rank a vulnerability based on your findings?

This depends on how much impact the vulnerability could affect your business. An example can answer this question., During your audit say you discover XSS and SQLi vulnerabilities. Both are equally dangerous, but in our scenario we rank XSS as the first most since the database that has the SQLi is not a production one and it is just holds some sample data. Thus we need to rank a vulnerability based on the risk factor.

15. What is an Active Directory? How does LDAP differs from Active Directory?

Active Directory is Microsoft’s implementation of directory service that provides information about the system, user’s activities, policies, etc. LDAP (LightWeight Directory Access Protocol) is a protocol that is used to query the directory services (in this case, the Actual Directory).

16. Give a simple difference between Authorization and Authentication?

Authorization is a process whereas an Authentication is a method. Authorization takes place during Authentication. This can be made clear with an example, Consider an ATM, You use your card to “authenticate” to that machine and once you have entered the correct pin you are “authorized” to do transacations.