How to Fix Cross-Site Scripting (XSS) in Vue
Learn how to prevent and fix Cross-Site Scripting (XSS) vulnerabilities in Vue applications. Step-by-step guide with code examples, security checklists, and best practices.
What Is Cross-Site Scripting (XSS)?
Cross-Site Scripting (XSS) is a code injection vulnerability that occurs when an application includes untrusted data in a web page without proper validation or escaping. An attacker can inject malicious scripts (typically JavaScript) that execute in the context of a victim's browser session.
There are three main types of XSS: Reflected XSS, where the malicious script comes from the current HTTP request; Stored XSS, where the script is permanently stored on the target server (e.g., in a database or comment field); and DOM-based XSS, where the vulnerability exists entirely in client-side code that processes data from an untrusted source.
Modern frameworks like React and Vue provide automatic output encoding by default, but developers can still introduce XSS through dangerous APIs like `dangerouslySetInnerHTML`, `v-html`, or by constructing HTML strings manually. Server-rendered pages are particularly vulnerable when user input flows into template output without sanitization.
Why It Matters
XSS is one of the most prevalent web vulnerabilities and can have devastating consequences. An attacker exploiting XSS can steal session cookies and authentication tokens, impersonate users and perform actions on their behalf, redirect users to malicious websites, deface web pages, and install keyloggers to capture credentials. Because XSS executes in the trusted context of the vulnerable website, it can bypass same-origin policies and access any data the user can see. In applications handling sensitive data -- financial records, health information, or personal communications -- XSS can lead to massive data breaches and regulatory violations.
How to Fix It in Vue
The primary defense against XSS is output encoding: escape all untrusted data before inserting it into HTML, JavaScript, CSS, or URL contexts. Use your framework's built-in auto-escaping (React JSX, Vue templates, Angular interpolation) and avoid bypassing it with dangerous APIs. Implement a strict Content Security Policy (CSP) that prevents inline script execution. Validate and sanitize all user input on the server side using allowlists rather than denylists. For rich text, use a proven sanitization library like DOMPurify. Set the HttpOnly flag on session cookies to prevent JavaScript access. Use the X-XSS-Protection header as an additional layer of defense.
Vue-Specific Advice
- Never use `v-html` with unsanitized user input. Vue's template interpolation `{{ }}` auto-escapes HTML, but `v-html` does not.
- Avoid using `eval()` or `new Function()` in Vue components. Use computed properties and watchers for dynamic behavior instead.
- Validate all props passed to components that render user-controlled content, especially in server-rendered (SSR) contexts.
- Use Vue Router's navigation guards to implement client-side route protection, but always enforce authorization on the server as well.
Code Examples
<template>
<!-- DANGEROUS -- raw HTML from user input -->
<div v-html="userComment" />
</template><template>
<!-- Safe: Vue auto-escapes text interpolation -->
<div>{{ userComment }}</div>
<!-- If HTML is needed, sanitize first -->
<div v-html="sanitizedComment" />
</template>
<script setup>
import DOMPurify from "dompurify";
import { computed } from "vue";
const props = defineProps({ userComment: String });
const sanitizedComment = computed(() =>
DOMPurify.sanitize(props.userComment)
);
</script>Vue Security Checklist for Cross-Site Scripting (XSS)
Vue Security Best Practices
Never use `v-html` with unsanitized user input. Vue's template interpolation `{{ }}` auto-escapes HTML, but `v-html` does not.
Avoid using `eval()` or `new Function()` in Vue components. Use computed properties and watchers for dynamic behavior instead.
Validate all props passed to components that render user-controlled content, especially in server-rendered (SSR) contexts.
Use Vue Router's navigation guards to implement client-side route protection, but always enforce authorization on the server as well.
Be cautious with Vue's `compile()` function, which can execute arbitrary code. Never pass user input to the template compiler.
Store sensitive configuration in environment variables prefixed per your build tool's convention (VITE_ for Vite) and never include secrets in client-side code.
Implement Content Security Policy headers to prevent inline script injection even if an XSS vulnerability exists.
Use Pinia stores carefully -- avoid storing sensitive data in state that persists across page navigations in SSR contexts.
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