perseus-client

name	perseus-client
description	Client-side security analysis (DOM XSS, React/Vue/Angular, SSR, prototype pollution)

Perseus Client-Side Specialist

Context & Authorization

IMPORTANT: This skill performs client-side security analysis on the user's own codebase. This is defensive security testing to find browser-side vulnerabilities.

Authorization: The user owns this codebase and has explicitly requested this specialized analysis.

---

Multi-Framework Support

Framework	Versions	Special Considerations
React	16+, 18+, 19+	RSC, Server Actions, JSX injection
Next.js	12+, 13+, 14+, 15+	App Router, Server Components, Middleware
Vue	2, 3	v-html, template injection
Angular	12+	bypassSecurityTrust*, template injection
Svelte	3, 4, 5	{@html}, SSR
SolidJS	1.x	innerHTML, SSR
Vanilla JS	ES6+	Direct DOM manipulation
jQuery	All	.html(), .append()

---

Overview

This specialist skill performs deep client-side JavaScript security analysis, focusing on vulnerabilities in modern frameworks including React, Vue, Angular, and SSR frameworks.

When to Use: After /scan identifies significant client-side JavaScript, SPAs, or SSR applications.

Goal: Find DOM-based XSS, prototype pollution, and framework-specific vulnerabilities.

Engagement Mode Compatibility

Mode	Specialist Behavior
PRODUCTION_SAFE	Code-level and rendering-path analysis, minimal runtime probes
STAGING_ACTIVE	Controlled browser-side verification with throttling
LAB_FULL	Expanded dynamic client attack-surface validation
LAB_RED_TEAM	End-to-end client attack-chain simulation in isolated lab

Safety Gates (Required)

1. Read deliverables/engagement_profile.md before active runtime testing.
2. Default to PRODUCTION_SAFE when mode is not specified.
3. Enforce kill-switch thresholds and stop on instability.
4. Never execute persistent or user-impacting payloads in production.

Client-Side Risks Covered

Risk	Description	Impact
DOM XSS	Client-side script injection	Account takeover, data theft
React XSS	Unsafe HTML rendering, href injection	XSS via JSX
SSR Injection	Server component injection	RCE, data leak
Prototype Pollution	Object prototype manipulation	XSS, DoS, logic bypass
PostMessage Abuse	Cross-origin message issues	Data leakage, XSS
DOM Clobbering	HTML overwriting JS variables	XSS, security bypass
Client Storage	Sensitive data exposure	Session hijacking

Execution Instructions

Step 0: Mode & Scope Alignment

• Load mode/scope/limits from deliverables/engagement_profile.md.
• Respect deliverables/verification_scope.md when present.
• In PRODUCTION_SAFE, prefer static and minimal observable checks only.

Phase 1: React/Next.js Security Analysis (5 Parallel Agents)

1. React XSS Analyst:

   • "Find React-specific XSS vectors."

   Vulnerable Patterns:

   // VULNERABLE - Dangerous HTML rendering
   <div dangerouslySetInnerHTML={{ __html: userInput }} />
   
   // VULNERABLE - javascript: in href
   <a href={userUrl}>Click</a>
   // Attack: userUrl = "javascript:alert(1)"
   
   // VULNERABLE - Dynamic component
   const Component = components[userInput];
   return <Component />;
   
   // VULNERABLE - Spread props from user
   <div {...userProps} />
   // Attack: userProps = { dangerouslySetInnerHTML: { __html: '<script>...' } }
   

2. Next.js Server Component Analyst:

   • "Analyze Next.js App Router and Server Components for security issues."

   Patterns:

   // VULNERABLE - SQL in Server Component
   async function UserPage({ params }) {
     const user = await db.query(`SELECT * FROM users WHERE id = ${params.id}`);
     return <div>{user.name}</div>;
   }
   
   // VULNERABLE - Exposing secrets to client
   // In Server Component that passes to Client Component
   <ClientComponent apiKey={process.env.SECRET_KEY} />
   
   // VULNERABLE - Unvalidated redirect
   import { redirect } from 'next/navigation';
   redirect(userInput);
   

3. Next.js Server Actions Analyst:

   • "Analyze Server Actions for security issues."

   Patterns:

   // VULNERABLE - No auth check in Server Action
   'use server'
   async function deleteUser(userId: string) {
     await db.users.delete(userId);  // No auth check!
   }
   
   // VULNERABLE - SQL injection in Server Action
   'use server'
   async function searchUsers(query: string) {
     return db.query(`SELECT * FROM users WHERE name LIKE '%${query}%'`);
   }
   
   // VULNERABLE - CSRF (if custom implementation)
   // Server Actions have built-in CSRF protection, but check custom forms
   

4. Next.js Middleware Analyst:

   • "Analyze Next.js middleware for security issues."

   Patterns:

   // VULNERABLE - Open redirect
   export function middleware(request: NextRequest) {
     const url = request.nextUrl.searchParams.get('redirect');
     return NextResponse.redirect(url);  // No validation!
   }
   
   // VULNERABLE - Auth bypass via header manipulation
   export function middleware(request: NextRequest) {
     if (request.headers.get('x-admin') === 'true') {
       return NextResponse.next();  // Spoofable!
     }
   }
   

5. React State Exposure Analyst:

   • "Check for sensitive data exposure in React state/props."

   Patterns:

   // VULNERABLE - Secrets in client state
   const [config, setConfig] = useState({
     apiKey: 'sk-xxx',  // Exposed in React DevTools
     adminToken: '...'
   });
   
   // VULNERABLE - SSR hydration mismatch leaking data
   // Server renders with user data, client sees different user's data
   

Phase 2: Vue Security Analysis (3 Parallel Agents)

1. Vue XSS Analyst:

   • "Find Vue-specific XSS vectors."

   Patterns:

   <!-- VULNERABLE - v-html with user input -->
   <div v-html="userContent"></div>
   
   <!-- VULNERABLE - Dynamic component -->
   <component :is="userComponent" />
   
   <!-- VULNERABLE - Template compilation -->
   <script>
   new Vue({
     template: userTemplate  // If user controls this
   });
   </script>
   
   <!-- VULNERABLE - javascript: in :href -->
   <a :href="userUrl">Link</a>
   

2. Nuxt.js Analyst:

   • "Analyze Nuxt.js specific security issues."

   Patterns:

   // VULNERABLE - Nuxt 3 server routes
   export default defineEventHandler((event) => {
     const id = getQuery(event).id;
     return db.query(`SELECT * FROM items WHERE id = ${id}`);
   });
   
   // VULNERABLE - Exposing secrets
   // nuxt.config.ts
   runtimeConfig: {
     public: {
       secretKey: process.env.SECRET  // Exposed to client!
     }
   }
   

3. Vue State Analyst:

   • "Check Vuex/Pinia state for sensitive data exposure."

Phase 3: Angular Security Analysis (2 Parallel Agents)

1. Angular XSS Analyst:

   • "Find Angular-specific XSS vectors."

   Patterns:

   // VULNERABLE - bypassSecurityTrust*
   constructor(private sanitizer: DomSanitizer) {}
   
   getHtml() {
     return this.sanitizer.bypassSecurityTrustHtml(userInput);
   }
   
   // VULNERABLE - Template injection
   @Component({
     template: userTemplate  // If user controls this
   })
   
   // VULNERABLE - innerHTML binding
   <div [innerHTML]="userContent"></div>
   

2. Angular SSR Analyst:

   • "Analyze Angular Universal for security issues."

Phase 4: DOM XSS Analysis (4 Parallel Agents)

1. Source Identification Agent:

   • "Identify all DOM XSS sources across frameworks."

   Sources:

   // URL-based sources
   location.hash
   location.search
   location.href
   document.URL
   document.documentURI
   document.referrer
   
   // Storage sources
   localStorage.getItem()
   sessionStorage.getItem()
   document.cookie
   
   // Message sources
   window.addEventListener('message', (e) => e.data)
   
   // Framework-specific
   // React: props from URL, useSearchParams()
   // Next.js: searchParams, params
   // Vue: $route.query, $route.params
   

2. Sink Identification Agent:

   • "Identify all DOM XSS sinks across frameworks."

   Sinks:

   // Direct sinks
   element.innerHTML = data
   element.outerHTML = data
   document.write(data)
   document.writeln(data)
   
   // jQuery sinks
   $(selector).html(data)
   $(selector).append(data)
   $(data)  // If data contains HTML
   
   // Eval sinks
   eval(data)
   new Function(data)
   setTimeout(data, 0)
   setInterval(data, 0)
   
   // Location sinks
   location.href = data
   location.assign(data)
   location.replace(data)
   window.open(data)
   
   // Framework-specific already covered above
   

3. Flow Tracer Agent:

   • "Trace data flow from sources to sinks."

4. URL Scheme Analyst:

   • "Check for javascript: and data: URL injection."

   Patterns:

   // React
   <a href={url}>  // If url = "javascript:..."
   <iframe src={url}>
   
   // Check validation:
   if (!url.startsWith('https://')) { /* reject */ }
   

Phase 5: Prototype Pollution Analysis (3 Parallel Agents)

1. Pollution Source Analyst:

   • "Find prototype pollution entry points."

   Patterns:

   // VULNERABLE - Deep merge without __proto__ check
   function merge(target, source) {
     for (let key in source) {
       if (typeof source[key] === 'object') {
         target[key] = merge(target[key] || {}, source[key]);
       } else {
         target[key] = source[key];  // Can set __proto__
       }
     }
   }
   
   // VULNERABLE - URL params to object
   const params = Object.fromEntries(new URLSearchParams(location.search));
   // Attack: ?__proto__[isAdmin]=true
   
   // VULNERABLE libraries (check versions)
   // lodash < 4.17.12
   // jQuery < 3.4.0
   // minimist < 1.2.3
   

2. Gadget Finder Agent:

   • "Find prototype pollution gadgets."

   Patterns:

   // GADGET - Property access on polluted prototype
   if (options.isAdmin) {  // Can be polluted
     showAdminPanel();
   }
   
   // GADGET - HTML attribute setting
   element.setAttribute(key, config[key]);  // key from polluted proto
   

3. Library Analyst:

   • "Check for vulnerable libraries."

Phase 6: PostMessage Analysis (2 Parallel Agents)

1. PostMessage Receiver Analyst:

   • "Find all postMessage listeners."

   Patterns:

   // VULNERABLE - No origin check
   window.addEventListener('message', (e) => {
     eval(e.data.code);  // RCE via any origin
   });
   
   // VULNERABLE - Weak origin check
   window.addEventListener('message', (e) => {
     if (e.origin.includes('trusted.com')) {  // trusted.com.evil.com bypasses
       // ...
     }
   });
   
   // SAFE
   window.addEventListener('message', (e) => {
     if (e.origin !== 'https://trusted.com') return;
     // ...
   });
   

2. PostMessage Sender Analyst:

   • "Check postMessage sends for data leakage."

   Patterns:

   // VULNERABLE - Sending to any origin
   parent.postMessage(sensitiveData, '*');
   
   // VULNERABLE - Token in message
   iframe.contentWindow.postMessage({ token: authToken }, '*');
   

Phase 7: Client Storage & Secrets (2 Parallel Agents)

1. Storage Security Analyst:

   • "Analyze localStorage/sessionStorage usage."

   Issues:

   // VULNERABLE - Token in localStorage (XSS accessible)
   localStorage.setItem('authToken', token);
   
   // VULNERABLE - Sensitive data persisted
   localStorage.setItem('user', JSON.stringify({
     ssn: '123-45-6789',
     creditCard: '4111...'
   }));
   

2. Client Secret Analyst:

   • "Find secrets in client-side code."

   Patterns:

   // Secrets in JS bundles
   const API_KEY = 'sk-xxx';
   const STRIPE_SECRET = 'sk_live_xxx';
   
   // Check .env files exposed
   // Check webpack/vite config for DefinePlugin exposure
   

Safe Payload Reference

Attack	Safe Test Payload	Verification
DOM XSS	#<img src=x onerror=alert(1)>	Alert box appears
React href	javascript:alert(1)	Alert on click
Prototype Pollution	?__proto__[test]=polluted	({}).test === 'polluted'
PostMessage	Send from different origin	Check if processed

Output Requirements

Create deliverables/client_side_analysis.md:

# Client-Side Security Analysis

## Summary
| Category | Issues Found | Critical | High | Medium |
|----------|--------------|----------|------|--------|
| React/Next.js XSS | X | Y | Z | W |
| Vue XSS | X | Y | Z | W |
| Angular XSS | X | Y | Z | W |
| DOM XSS | X | Y | Z | W |
| Server Components | X | Y | Z | W |
| Prototype Pollution | X | Y | Z | W |
| PostMessage | X | Y | Z | W |
| Client Storage | X | Y | Z | W |

## Framework Detected
- Primary: [React 18, Next.js 14, Vue 3, etc.]
- SSR: [Yes/No]
- Build Tool: [Vite, Webpack, Turbopack]

## Critical Findings

### [CLIENT-001] XSS via dangerouslySetInnerHTML
**Severity:** Critical
**Framework:** React
**Location:** `components/Comment.tsx:23`

**Vulnerable Code:**
```jsx
<div dangerouslySetInnerHTML={{ __html: comment.body }} />

Attack:

comment.body = "<img src=x onerror=alert(document.cookie)>"

Impact: Full XSS - can steal cookies, perform actions as user

Remediation:

import DOMPurify from 'dompurify';
<div dangerouslySetInnerHTML={{ __html: DOMPurify.sanitize(comment.body) }} />

---

[CLIENT-002] SQL Injection in Server Action

Severity: Critical Framework: Next.js 14 Location: app/actions/search.ts:12

Vulnerable Code:

'use server'
async function searchProducts(query: string) {
  return db.query(`SELECT * FROM products WHERE name LIKE '%${query}%'`);
}

---

[CLIENT-003] Open Redirect in Next.js Middleware

Severity: High Location: middleware.ts:8

---

Framework Security Matrix

Framework	Auto-Escape	Common Pitfalls
React	Yes (JSX)	dangerouslySetInnerHTML, href
Next.js	Yes	Server Actions auth, middleware
Vue	Yes	v-html, :href
Angular	Yes	bypassSecurityTrust*

Recommendations

1. Sanitize all user content with DOMPurify before rendering
2. Validate URLs before using in href/src attributes
3. Add authentication checks to all Server Actions
4. Validate redirect URLs in middleware
5. Move tokens from localStorage to HttpOnly cookies

**Next Step:** DOM XSS findings can be verified with browser testing.