Security Fundamentals Interview Questions for Cyber Security
26 Security Fundamentals questions with answers for cyber security roles — 15 easy, 9 medium, 2 hard.
About Security Fundamentals
Start with the core ideas every security role uses: the CIA triad, threats, vulnerabilities and risk, defence in depth, least privilege, Zero Trust, malware types, social engineering and frameworks like the Cyber Kill Chain and MITRE ATT&CK. These basics appear in almost every fresher interview and shape how you reason about any security decision.
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The CIA triad is Confidentiality, Integrity and Availability, the three goals every control supports. Confidentiality keeps data away from unauthorised people, for example with encryption and access control. Integrity ensures data is not altered without detection, using hashes and digital signatures. Availability keeps systems usable when needed, through backups, redundancy and DDoS protection. Most security decisions are a trade-off between these three.
02
What is the difference between a threat, a vulnerability and a risk?
A vulnerability is a weakness, such as an unpatched server. A threat is anything that can exploit it, such as a ransomware group. Risk is the likelihood that the threat exploits the vulnerability multiplied by the business impact. For example, an unpatched internet-facing VPN is high risk, while the same flaw on an isolated lab machine is low risk because likelihood and impact are smaller.
Defence in depth means using several independent layers of controls so that one failure does not lead to a breach. A typical stack has perimeter firewalls, email filtering, endpoint EDR, MFA, network segmentation, least privilege, logging and backups. If a phishing email gets past the filter, MFA and EDR can still stop the attacker. The trade-off is cost and complexity, so layers should target the most likely attack paths.
Least privilege means every user, service and application gets only the minimum access needed for its job, and only for as long as needed. It limits the damage from compromised accounts and insider mistakes. Examples are giving developers read-only production access, using separate admin accounts, and just-in-time elevation that expires after a few hours. Regular access reviews are needed because permissions tend to grow over time.
05
Explain the difference between symmetric and asymmetric encryption at a basic level.
Symmetric encryption uses one shared key for encryption and decryption, such as AES; it is fast and used for bulk data. Asymmetric encryption uses a public and private key pair, such as RSA or elliptic curve keys; it is slower but solves key distribution and enables digital signatures. Real protocols like TLS combine them: asymmetric methods agree on a session key, then AES encrypts the traffic.
06
What is the difference between hashing and encryption?
Encryption is reversible with the right key and protects confidentiality. Hashing is a one-way function that produces a fixed-length digest and is used for integrity checks and password storage. SHA-256 of a file lets you detect tampering, but you cannot get the file back from the hash. Passwords should be stored with slow salted hashes such as Argon2id or bcrypt, never encrypted or with plain SHA-256.
07
What is social engineering and what are its common forms?
Social engineering manipulates people rather than technology to gain access or information. Common forms are phishing emails, spear phishing aimed at specific staff, vishing over phone calls, smishing over SMS or WhatsApp, pretexting with a fake story, baiting with infected USB drives and tailgating into offices. Defences include awareness training, phishing simulations, call-back verification for payment changes, and technical controls such as MFA and email authentication.
08
What is malware and how do virus, worm, trojan and ransomware differ?
Malware is any software built to harm or misuse a system. A virus attaches to files and spreads when they run. A worm spreads by itself across networks, often using a vulnerability. A trojan pretends to be legitimate software to trick users into installing it. Ransomware encrypts or steals data and demands payment, and modern groups use double extortion by threatening to leak stolen data.
09
What is the difference between a vulnerability assessment and a penetration test?
A vulnerability assessment uses scanners to find and rank as many known weaknesses as possible across many assets, and it is broad and frequent. A penetration test is a time-boxed, authorised attempt to exploit weaknesses and show real impact, such as reaching sensitive data. Assessments answer what is wrong; pen tests answer what an attacker could actually achieve. Most programmes run monthly scans and annual or release-based pen tests.
10
What is the difference between authentication, authorisation and accounting?
Authentication proves who you are, for example password plus an OTP or passkey. Authorisation decides what you are allowed to do after login, such as read-only access to a finance folder. Accounting, or auditing, records what you actually did, like logins, file access and admin changes. Together they are called AAA. Weak accounting is a common gap, because without logs an incident cannot be investigated.
11
Tell me about a time you found a security issue that nobody asked you to look at.
Situation: while setting up a college lab server, I noticed the admin panel of our event website was reachable without login. Task: report it responsibly. Action: I confirmed the issue without accessing any data, wrote a short note with steps and impact, and shared it privately with the faculty in charge. Result: it was fixed in two days and I was asked to review the next release.
12
How would you verify the integrity of a downloaded installer on Windows and Linux?
Compare the file's hash with the value published by the vendor over a trusted channel, or verify its digital signature. On Windows, use PowerShell and check the Authenticode signature. On Linux, use sha256sum and gpg for signed checksum files.
Get-FileHash .\setup.exe -Algorithm SHA256
Get-AuthenticodeSignature .\setup.exe
sha256sum tool.tar.gz
gpg --verify SHA256SUMS.asc SHA256SUMS
13
How do you generate a strong random secret or password from the command line?
Use a cryptographically secure source, never a simple random function. OpenSSL and Python's secrets module both use the operating system CSPRNG.
openssl rand -base64 32
python3 -c "import secrets; print(secrets.token_urlsafe(32))"
Store the output in a password manager or secret vault, not in a text file or chat message.
14
How do you check which ports are listening on a server you manage?
List listening sockets with the owning process, then compare against what the server should expose. Anything unexpected needs an owner or should be closed.
# Linux
sudo ss -tulpn
# Windows
netstat -ano | findstr LISTENING
Get-NetTCPConnection -State Listen
Map the PID to a process name in Task Manager or with ps to identify the service.
15
Why do you want to build a career in cyber security?
A good answer links genuine interest to evidence. For example: I got interested after investigating a phishing email that reached my college group, which led me to study networking and complete Security+. I built a home lab with a SIEM and wrote detections for brute-force logins. I enjoy problem solving under pressure, and I want to grow in a SOC, then specialise in incident response.
The Lockheed Martin Cyber Kill Chain describes seven stages of an intrusion: reconnaissance, weaponisation, delivery, exploitation, installation, command and control, and actions on objectives. Defenders use it to map controls to each stage, for example email filtering at delivery and egress filtering at command and control. Its weakness is a perimeter focus, so many teams pair it with MITRE ATT&CK for detailed techniques after initial access.
MITRE ATT&CK is a public knowledge base of adversary tactics and techniques observed in real attacks, organised in matrices for Enterprise, Mobile and ICS. Tactics are the goal, such as Persistence, and techniques are the method, such as T1053 Scheduled Task. Teams use it to map detection coverage, write threat-informed detections, plan red and purple team exercises, and describe incidents in a common language.
Zero Trust removes implicit trust based on network location. Every request is verified using identity, device health and context, access is least privilege and granted per session, and the environment is assumed to be already breached. NIST SP 800-207 describes the model. In practice it means strong MFA, device posture checks, identity-aware proxies instead of flat VPN access, micro-segmentation and continuous monitoring. It is a journey, not a single product.
19
Your manager asks why the company needs security when it already has antivirus on every laptop. How do you explain?
I would explain that antivirus mainly blocks known malicious files, while most modern attacks use stolen credentials, phishing links, living-off-the-land tools like PowerShell, or cloud misconfigurations that antivirus never sees. I would map our top risks to missing controls, such as MFA, EDR, logging and backups, and use a recent real incident pattern to show business impact in downtime and regulatory reporting cost.
20
A user reports a pop-up saying their files are encrypted. What are your first steps?
First, isolate the device from the network, ideally through EDR network containment, without powering it off so memory evidence is kept. Inform the incident lead and start a timeline. Check for the same indicators on other hosts, disable the user's sessions and reset credentials if needed, and identify the ransomware family from the note. Then confirm backups are intact and offline before any recovery begins.
21
A developer has hardcoded database passwords in a public code repository. What do you do?
Treat the secret as compromised immediately, even if the commit is removed, because public repos are scraped within minutes. Rotate the password and any related keys, check database logs for unknown logins since the commit time, and remove the secret from git history. Then fix the root cause by moving secrets to a vault or cloud secret manager and adding secret scanning to pre-commit hooks and the CI pipeline.
22
Leadership wants to block all USB drives tomorrow. How would you handle this request?
I would support the goal but plan the rollout to avoid breaking business work. First, find who genuinely needs USB, such as field engineers, using endpoint logs. Then apply a device control policy through EDR or Intune that blocks mass storage by default, allows approved encrypted devices by serial number, and logs exceptions. Communicate the change, pilot it with one department, then enforce company wide.
23
How would you run a basic threat model for a new web application?
Draw a data flow diagram showing users, the web app, APIs, databases and third parties, and mark trust boundaries. Then apply STRIDE to each element: Spoofing, Tampering, Repudiation, Information disclosure, Denial of service and Elevation of privilege. For each threat, record the existing control, a risk rating and an owner. Repeat the model whenever the architecture changes, ideally during design reviews.
24
Tell me about a time you explained a security risk to a non-technical person.
Situation: my team lead in a support role wanted to share admin passwords on a spreadsheet. Task: change this without slowing the team. Action: I explained the risk as a house key copied for everyone, showed how one leaked laptop exposes all systems, and proposed a password manager with shared vaults. Result: we adopted it within a week and audit findings dropped.
25
A vendor announces a zero-day in your internet-facing appliance with no patch yet. What does that mean and how do you protect the company?
A zero-day is a flaw that the vendor does not know about or has not yet patched, so defenders have had zero days to fix it. Exploits for zero-days are valuable and often used in targeted attacks. Since patches are unavailable, defence relies on layered controls: EDR behaviour detection, network segmentation, least privilege, virtual patching with WAF or IPS rules, and fast patching once a fix is released.
26
How do you prioritise 500 vulnerabilities found in a scan?
CVSS alone is not enough. I combine severity with exploitability and exposure: check the CISA Known Exploited Vulnerabilities list and EPSS score, whether the asset is internet facing, and how critical the business data on it is. Internet-facing systems with known exploited flaws are fixed first, often within days. Internal low-severity findings go into normal patch cycles. Group fixes by patch to reduce effort.
Frequently asked questions
How important is Security Fundamentals in Cyber Security interviews?
Start with the core ideas every security role uses: the CIA triad, threats, vulnerabilities and risk, defence in depth, least privilege, Zero Trust, malware types, social engineering and frameworks like the Cyber Kill Chain and MITRE ATT&CK. These basics appear in almost every fresher interview and shape how you reason about any security decision.
How should I use the Security Fundamentals sheet?
Go top to bottom — easy to hard. Answer before opening each answer, tick what you solved and save misses to Last-Minute Revision.