Why security matters in Vue - Challenge Your Understanding

Challenge - 5 Problems

🧠 Conceptual

intermediate

Understanding Cross-Site Scripting (XSS) in Vue

What is the main reason Vue automatically escapes HTML in template bindings?

A To prevent attackers from injecting malicious scripts into the app

B To make the app load faster by skipping HTML parsing

C To allow users to write raw HTML in templates without errors

D To enable Vue to style elements automatically

💡 Hint

Think about what happens if user input contains script tags.

Vue escapes HTML in template bindings to stop attackers from running harmful scripts inside your app, which is called Cross-Site Scripting (XSS).

❓ component_behavior

intermediate

Safe Rendering with v-html Directive

What happens if you use v-html with untrusted user input in Vue?

Vue

<template>
  <div v-html="userContent"></div>
</template>

<script setup>
const userContent = '<img src=x onerror=alert(1)>'
</script>

A Vue automatically sanitizes the HTML to remove scripts

B Vue throws an error and stops rendering

C The content is displayed as plain text, no HTML rendered

D The malicious script runs, causing a security risk

💡 Hint

Consider what v-html does with raw HTML strings.

The v-html directive renders raw HTML, so if the content includes malicious scripts, they will run unless you sanitize the input yourself.

🔧 Debug

advanced

Identifying a Security Flaw in Vue Code

Which option shows a Vue snippet that can cause a security vulnerability?

A <template><div>{{ userInput }}</div></template><script setup>const userInput = '<script>alert(1)</script>'</script>

B <template><div v-html="userInput"></div></template><script setup>const userInput = '<script>alert(1)</script>'</script>

C <template><div>{{ userInput }}</div></template><script setup>const userInput = 'Hello World'</script>

D <template><div>{{ userInput }}</div></template><script setup>const userInput = '&lt;script&gt;alert(1)&lt;/script&gt;'</script>

💡 Hint

Look for where raw HTML is rendered without escaping.

Option B uses v-html with raw script tags, which will execute the script and cause an XSS vulnerability.

❓ state_output

advanced

Effect of Sanitizing User Input Before Rendering

If you sanitize user input to remove scripts before assigning it to a Vue reactive variable used with v-html, what will be the output?

Vue

<template>
  <div v-html="safeContent"></div>
</template>

<script setup>
import DOMPurify from 'dompurify'
const rawContent = '<img src=x onerror=alert(1)><p>Hello</p>'
const safeContent = DOMPurify.sanitize(rawContent)
</script>

A Nothing is rendered because the content is blocked

B The malicious script runs and <p>Hello</p> is shown

C Only the <p>Hello</p> is rendered; the malicious script is removed

D Vue throws an error because of the sanitizer

💡 Hint

Think about what sanitizing does to dangerous HTML.

Sanitizing removes harmful parts like scripts but keeps safe HTML tags, so only safe content is rendered.

📝 Syntax

expert

Correct Syntax to Bind Attributes Safely in Vue

Which option correctly binds a user-provided URL to an img tag's src attribute to avoid security issues?

A <img :src="userUrl" alt="User image">

B <img src="{{ userUrl }}" alt="User image">

C <img v-bind:src="userUrl" alt="User image" v-html="userUrl">

D <img src="userUrl" alt="User image">

💡 Hint

Remember how Vue binds dynamic attributes safely.

Using :src or v-bind:src safely binds the URL as an attribute, preventing injection. Using mustache inside src or plain strings does not work correctly.

Practice

1. Why is security important when building Vue applications?

easy

A. To reduce the size of the Vue library

B. To make the app load faster

C. To protect users from malicious attacks like cross-site scripting (XSS)

D. To add more animations and effects

Solution

1. Step 1: Understand the purpose of security in web apps

   Security protects users and data from harmful actions like hacking or data theft.

2. Step 2: Identify common security risks in Vue apps

   Cross-site scripting (XSS) is a common risk where attackers inject harmful code into the app.

3. Final Answer:

   To protect users from malicious attacks like cross-site scripting (XSS) -> Option C

4. Quick Check:

   Security = Protect users from attacks [OK]

Hint: Security protects users from harmful code injections [OK]

Common Mistakes:

• Confusing security with performance
• Thinking security only affects backend
• Believing Vue automatically prevents all risks

2. Which Vue syntax is safe to display user content without risking XSS attacks?

easy

A. <div>{{ userContent }}</div>

B. <div v-html="userContent"></div>

C. <div>{{{ userContent }}}</div>

D. <div v-text="userContent"></div>

Solution

1. Step 1: Understand Vue's default escaping

   Using double curly braces {{ }} automatically escapes HTML, preventing XSS.

2. Step 2: Compare with other options

   v-html and triple braces {{{ }}} insert raw HTML, which can be unsafe. v-text also escapes but renders text only.

3. Final Answer:

   <div>{{ userContent }}</div> -> Option A

4. Quick Check:

   Double braces escape HTML = safe [OK]

Hint: Use {{ }} to safely display user content in Vue [OK]

Common Mistakes:

• Using v-html without sanitizing content
• Confusing triple braces with double braces
• Assuming v-text allows HTML rendering

3. What will be the rendered output of this Vue template if userInput is '<script>alert("XSS")</script>Hello'?

<template>
  <div>{{ userInput }}</div>
</template>

medium

A. <script>alert("XSS")</script>Hello (script runs)

B. Empty div with no content

C. Hello only

D. <script>alert("XSS")</script>Hello (script shown as text)

Solution

1. Step 1: Understand Vue's interpolation escaping

   Using {{ userInput }} escapes HTML tags, so script tags are shown as text, not executed.

2. Step 2: Predict the output

   The script tags appear as text, followed by 'Hello', so the full string is visible safely.

3. Final Answer:

   <script>alert("XSS")</script>Hello (script shown as text) -> Option D

4. Quick Check:

   Escaped HTML shows tags as text [OK]

Hint: {{ }} escapes HTML, so scripts show as text, not run [OK]

Common Mistakes:

• Thinking script runs inside {{ }}
• Expecting only 'Hello' to show
• Confusing raw HTML insertion with interpolation

4. You have this Vue code:

<template>
  <div v-html="rawHtml"></div>
</template>

<script setup>
const rawHtml = ''
</script>

What is the main security problem here?

medium

A. v-html renders raw HTML which can run malicious scripts

B. The img tag is invalid and causes syntax errors

C. Vue automatically sanitizes v-html content, so no problem

D. Using const for rawHtml causes reactivity issues

Solution

1. Step 1: Understand v-html behavior

   v-html inserts raw HTML into the DOM without escaping, so scripts can run.

2. Step 2: Identify the risk in the example

   The img tag has an onerror attribute that triggers alert(1), a common XSS attack vector.

3. Final Answer:

   v-html renders raw HTML which can run malicious scripts -> Option A

4. Quick Check:

   v-html = raw HTML injection risk [OK]

Hint: v-html inserts raw HTML; sanitize before use [OK]

Common Mistakes:

• Assuming Vue sanitizes v-html automatically
• Confusing syntax errors with security issues
• Thinking const affects security

5. You want to safely display user comments that may contain some HTML tags like <b> and <i> but prevent any scripts. Which approach best balances security and formatting in Vue?

hard

A. Escape all HTML tags and show comments as plain text

B. Sanitize user comments to allow only safe tags, then use v-html

C. Use v-html directly on user comments without filtering

D. Use triple braces {{{ comment }}} to render raw HTML

Solution

1. Step 1: Understand the need for safe HTML rendering

   Allowing some HTML tags improves formatting but raw HTML can be dangerous.

2. Step 2: Choose a method to allow safe tags only

   Sanitizing user input removes harmful scripts but keeps allowed tags, then v-html safely renders it.

3. Final Answer:

   Sanitize user comments to allow only safe tags, then use v-html -> Option B

4. Quick Check:

   Sanitize then v-html = safe formatted output [OK]

Hint: Sanitize input before v-html to allow safe HTML [OK]

Common Mistakes:

• Using v-html without sanitizing
• Escaping all HTML losing formatting
• Using triple braces which is unsafe