Implementing Browser Isolation for Zero Trust

When to Use

• When deploying remote browser isolation as part of a Zero Trust security architecture
• When protecting users from zero-day browser exploits and drive-by downloads
• When implementing content disarming and reconstruction for file downloads
• When enforcing data loss prevention policies for web browsing sessions
• When securing access to untrusted or uncategorized websites
• When integrating browser isolation with existing SWG and ZTNA infrastructure
• When protecting against phishing and credential theft via isolated rendering

Prerequisites

• Familiarity with Zero Trust architecture principles and network security
• Understanding of Secure Web Gateway (SWG) and proxy deployment models
• Access to a test or lab environment for policy validation
• Python 3.8+ with required dependencies installed
• DNS and proxy infrastructure for traffic routing

Instructions

Phase 1: URL Categorization and Risk Classification

Build a URL categorization engine that classifies websites by risk level to determine isolation policy. URLs are scored based on threat intelligence feeds, domain reputation, content category, and historical risk indicators.

from agent import BrowserIsolationPolicyEngine

engine = BrowserIsolationPolicyEngine(
    organization="Acme Corp",
    default_isolation_mode="isolate_risky",
)

# Classify a URL and determine isolation action
result = engine.classify_url("https://docs.google.com/spreadsheets/d/abc123")
print(f"Category: {result['category']}")
print(f"Risk Level: {result['risk_level']}")
print(f"Isolation Action: {result['action']}")
# Output: Category: cloud_productivity
#         Risk Level: low
#         Action: allow_direct

result = engine.classify_url("https://unknown-sketchy-domain.xyz/download.html")
print(f"Category: {result['category']}")
print(f"Risk Level: {result['risk_level']}")
print(f"Isolation Action: {result['action']}")
# Output: Category: uncategorized
#         Risk Level: high
#         Action: full_isolation

Phase 2: Isolation Policy Configuration

Define isolation policies that map URL categories and risk levels to specific isolation modes and DLP restrictions. Policies support granular controls including clipboard, file download, upload, and printing restrictions.

# Configure isolation policies
engine.add_isolation_policy(
    name="Block Uncategorized Sites",
    description="Fully isolate all uncategorized or newly registered domains",
    match_criteria={
        "url_categories": ["uncategorized", "newly_registered"],
        "risk_levels": ["high", "critical"],
    },
    isolation_mode="full_isolation",
    dlp_controls={
        "disable_copy_paste": True,
        "disable_download": True,
        "disable_upload": True,
        "disable_printing": True,
        "disable_keyboard_input": False,
        "watermark_session": True,
    },
)

engine.add_isolation_policy(
    name="Isolate Webmail with DLP",
    description="Isolate personal webmail with download restrictions",
    match_criteria={
        "url_categories": ["webmail"],
        "domains": ["mail.google.com", "outlook.live.com", "mail.yahoo.com"],
    },
    isolation_mode="read_only_isolation",
    dlp_controls={
        "disable_copy_paste": True,
        "disable_download": True,
        "disable_upload": True,
        "disable_printing": True,
        "disable_keyboard_input": False,
        "watermark_session": False,
    },
)

engine.add_isolation_policy(
    name="CDR for File Downloads",
    description="Apply content disarm and reconstruction to all file downloads",
    match_criteria={
        "url_categories": ["*"],
        "file_types": ["pdf", "docx", "xlsx", "pptx", "zip", "exe", "msi"],
    },
    isolation_mode="cdr_passthrough",
    cdr_config={
        "strip_macros": True,
        "strip_embedded_objects": True,
        "strip_javascript": True,
        "strip_active_content": True,
        "flatten_pdf": True,
        "reconstruct_to_safe_format": True,
        "max_file_size_mb": 50,
        "allowed_file_types": ["pdf", "docx", "xlsx", "pptx", "png", "jpg"],
    },
)

engine.add_isolation_policy(
    name="Allow Trusted SaaS Direct",
    description="Allow direct access to sanctioned SaaS applications",
    match_criteria={
        "url_categories": ["cloud_productivity", "business_saas"],
        "domains": [
            "*.office365.com", "*.office.com", "*.microsoft.com",

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