What is SQL injection, how does it happen, and how would you prevent it in a web application?

What the interviewer is looking for

• This question tests application security. Explains common vulnerabilities and fixes accurately, and builds security testing into development without blocking engineers.
• Strong answers: Untrusted input changes the query, attackers can read or modify data; fix with parameterised queries, input validation, and least-privilege database accounts.
• Likely follow-up: What other attacks come from the same root cause of trusting user input?

Another way it may be asked: Imagine a login form passes what the user types straight into a database query. What could go wrong, and how do you stop it?

A structure to follow: Answer, explain, example, limits

1. Step 1

   Answer

   Give your direct answer in the first sentence so the interviewer knows where you are going.

2. Step 2

   Explain

   Say how it works or why you would do it that way, in plain words before jargon.

3. Step 3

   Example

   Anchor it in something you have actually done or seen, with the detail that shows hands-on experience.

4. Step 4

   Limits

   Say when your approach would not be the right one. It shows judgement.

This is guidance on shape, not a script. Use your own real experience and facts; never invent details to fill a gap. See the STAR guide and answer frameworks.

Common slips

• Reciting a definition without showing you have applied it.
• Using terms you cannot explain if asked a level deeper.
• Claiming experience beyond what you can discuss in detail.

How to practise it

Say the answer in 90 seconds, then answer the follow-up as if it were a new question.

Related questions

• How would you add security checks to a development pipeline without making engineers wait or ignore the results?
• Tell me about a security issue you found or fixed that you are proud of. How did you discover it, and what was the impact?
• Why is multi-factor authentication important, and which kinds of second factor are stronger than others?
• You notice a user account logging in from two countries an hour apart. What would you check, and what would you do?
• A scanner reports three thousand vulnerabilities across your systems. How do you decide what to fix first?

Browse all questions