Security Blog

Managing Your External Attack Surface: A Comprehensive Guide

ariana@resilientx.com

The exponential growth of remote work, cloud adoption, third party access, and internet-connected devices has led to an explosion of enterprise external attack surfaces. As your digital footprint grows, so does your risk exposure. To defend your organization in today's complex threat landscape, you need to master external attack surface management.

Your external attack surface is the collection of all externally accessible digital entry points that could be potentially exploited by cybercriminals. These include your public cloud instances, websites, remote access portals, and connections with third party vendors.

As your external attack surface expands, you become more vulnerable to data breaches, service disruptions, intellectual property theft, and reputational damage. Legacy security tools are inadequate for managing such a dynamic environment. You need automated, intelligent solutions that provide complete visibility and control across your entire external attack surface.

In this comprehensive guide, we will cover everything you need to know about managing your enterprise external attack surface, including:

What is an external attack surface and why is it important?
Core components of an external attack surface
Best practices for managing external attack surface
Choosing the right external attack surface management platform
Integrating external attack surface data into your security stack
Leveraging automation to improve efficacy
Collaborating with third parties to reduce shared risk
Building a proactive vulnerability disclosure program
Creating an incident response plan for your external attack surface
Measuring the ROI of your external attack surface management program

Let's get started.

What is an External Attack Surface?

Your external attack surface consists of all the digital entry points outside your organization's firewall and network perimeter. These include:

Public cloud environments - instances, storage buckets, functions, APIs, etc.
Websites and web applications - your public online properties and apps.
Remote access portals - VPNs, RDP, SSH, etc.
Internet exposed services - databases, message queues, file shares, etc.
Network devices - load balancers, WAFs, proxies, etc.
APIs - public and third-party APIs.
Mobile apps - consumer and employee mobile apps.
Internet of Things (IoT) - connected building systems, medical devices, manufacturing equipment, etc.
Third party connections - vendor portals, digital supply chain integration, etc.
Subsidiaries and mergers & acquisitions (M&A) - expanded external footprint.

Any Internet-accessible digital asset that is not protected by your internal network security controls is part of your external attack surface. These uncontrolled assets represent points of entry for attackers to infiltrate your systems and data.

Why Manage Your External Attack Surface?

Here are some key reasons why gaining control over your external attack surface is critical:

Evolving threat landscape - External threats now account for over 80% of breaches. Attackers are sophisticated, well-funded, and constantly hunting for Internet-facing weaknesses.
Regulatory compliance - Regulations like PCI DSS, HIPAA, GDPR, and CCPA require you to manage risk across your entire digital footprint. Fines for non-compliance can be steep.
Third party risk - Interconnected digital ecosystems mean vulnerabilities anywhere along a supply chain can impact everyone.
Mergers & acquisitions - Inorganic growth quickly expands attack surface and introduces new risks.
Cloud adoption - Dynamic public cloud environments need specialized controls to prevent misconfigurations.
Remote workforce - More employees accessing systems externally increases exposure.
New attack vectors - Emerging technologies like IoT and APIs expand your attack surface.
Reputational damage - Breaches resulting from unmanaged externals assets causes loss of customer trust.

The challenge is that the external attack surface is growing too quickly and is too distributed for manual processes to keep pace. You need an automated way to continuously discover assets, assess risk, and mitigate vulnerabilities across the entirety of your external attack surface.

Components of the External Attack Surface

To master external attack surface management, you first need to understand the core components that comprise it. These are:

Assets

Anything that can be accessed and potentially exploited externally is an asset. This includes physical devices, applications, services, network components, APIs, code repositories, cloud resources, employee and partner portals, etc.

Dynamic discovery of all Internet-accessible assets across the enterprise footprint is the critical first step in external attack surface management. Comprehensive asset discovery is difficult because organizations often lack centralized visibility or an accurate central inventory of all external-facing assets.

Access Points

These are the digital entry points that allow external connections to interact with assets. For example:

IP addresses and open ports
Domain names
API endpoints
Database connection strings
Cloud service URLs
Web application logins
Remote access portals
Partner integration connections

Access points represent the doorways where attackers can attempt to gain entry and must be properly secured.

Vulnerabilities

These are software flaws, configuration issues, or policy gaps that create weaknesses in assets and access points. Examples include unpatched systems, insecure protocols, use of default passwords, overly permissive IAM policies, expired TLS certificates, etc.

Vulnerabilities are the specific issues that need to be addressed to reduce risk exposure.

Risk Profile

This refers to the potential business impact and likelihood of exploitation of vulnerabilities in your external attack surface assets and access points. For example, an unpatched Internet-facing server managing sensitive financial data carries higher risk than a test subdomain with limited access controls.

Understanding your external risk profile allows you to intelligently prioritize remediation based on potential damage.

Best Practices for External Attack Surface Management

Managing a dynamic external attack surface at scale requires thinking beyond the traditional perimeter. Here are 8 best practices modern enterprises follow:

1. Discover All External Assets

You can't protect what you can't see. Use both automated scanning and centralized asset inventory data to achieve comprehensive visibility across your entire external attack surface.

2. Continuously Monitor for New Assets

New assets get deployed constantly. Continuously scan to discover additions and changes so your visibility is always current.

3. Classify Assets and Data

Categorize assets by type, ownership, data sensitivity, and business criticality. This allows rational risk analysis.

4. Map All Access Points

Inventory all external connections to create a complete access point map. This reveals potential attack vectors.

5. Identify Vulnerabilities Early

Scan frequently to detect new vulnerabilities early, before they can be exploited.

6. Define Risk Profiles

Assign risk profiles to assets based on data sensitivity, vulnerability severity, and potential business impact. Focus remediation on addressing high risk issues first.

7. Orchestrate Remediation

Once vulnerabilities have been discovered and prioritized, auto-generate tickets and orchestrate remediation workflows using existing IT and SecOps systems.

8. Measure Risk Reduction Over Time

Quantify and track risk reduction over time to demonstrate improved resilience and compliance.

These best practices enable you to manage external risk intelligently, efficiently, and at scale.

Choosing an External Attack Surface Management Platform

To implement a comprehensive external attack surface management program, you need an automated SaaS platform purpose-built to address the unique challenges of a modern dynamic perimeter.

Here are the key capabilities to look for in an enterprise-grade EASM solution:

Asset Discovery - Both active scanning and integrations with CMDBs, cloud consoles, etc. to discover known and shadow assets.

Continuous Monitoring - Frequent scanning to detect assets and configuration drift.

Risk-Based Prioritization - Uses data science to calculate risk scoring based on multiple factors.

Centralized Intelligence - Single pane of glass view centralized across environments.

Auto-Remediation - Orchestrates remediation workflows across your IT and SecOps stack.

Compliance Reporting - Provides audit-ready reports mapped to regulatory requirements.

Third Party Integration - Assesses supplier risk and shares attack surface intelligence.

Attack Surface Analytics - Identifies root causes of issues and strategic remediations.

Collaboration Tools - Allows cross-team and third party cooperative resolution.

The most effective platforms provide layered defenses - combining software scanning with human auditing to achieve both scale and accuracy. Look for a vendor with experience in managing attack surface risk across diverse enterprise environments.

Integrating EASM Into Your Security Stack

The data gleaned from external attack surface management adds crucial context for other security tools. Here's how to integrate EASM into your broader security stack:

SIEM - Stream asset context, vulnerabilities, and risk scoring into your SIEM for improved monitoring and response.

SOAR - Trigger playbooks based on critical attack surface findings to enable automated response.

Vulnerability Management - Sync findings with your vuln management system to align scanning and remediation.

Application Security - Provide details on shadow exposed apps and appropriate security controls.

Cloud Security Posture Management - Combine insights from CSPM tools for a unified view of cloud risk.

Third Party Risk Management - Inform supplier risk scoring with attack surface data from interconnected partners.

Identity & Access Management - Manage credential hygiene and identity security based on EASM access point analysis.

Each of these integrations provides richer context that strengthens your overall security posture.

The Power of Automation in EASM

The massive scale and constant flux of the external attack surface makes manual management impractical. Automation is key to staying on top of external risk.

Some of the ways automation enhances EASM efficacy include:

Asset Discovery - Autonomous scanners map assets at scale faster than manual auditing.

Continuous Scanning - Scheduled scans monitor configuration drift 24/7 without human intervention.

Vulnerability Detection - Algorithmic analytics detect vulnerabilities with far greater accuracy than human eyes.

Risk Scoring - Data science models quantify risk context better than qualitative human assessment.

Auto-Remediation - Rules-based workflows fix or mitigate issues automatically without delays.

Third Party Integration - APIs share real-time attack surface data across partners at computer speed.

Reporting - Templatized reports save analysts time and ensure audit readiness.

The machine learning powered analytics of modern EASM platforms allow them to get smarter and faster over time - delivering sweeping visibility, early threat detection, and efficient workflows at enormous scale.

Managing Third Party Attack Surface Risk

Today's highly interconnected business ecosystems mean the external attack surface extends beyond your own environment into those of digital suppliers, partners, and subsidiaries. A compromise anywhere along an interconnected supply chain can create exposure for everyone.

Here's how to manage third party driven attack surface risk:

Know Your Connections - Map the entire digital supply chain to identify points of integration.

Assess Supplier Security - Examine partner environments for vulnerabilities that could propagate.

Limit Access - Only enable essential external connections and limit privileges.

Share Intelligence - Provide partners attack surface data to incentivize remediation.

Align Security Standards - Include your security protocols and formats in supplier contracts.

Manage Secrets - Rotate API keys/tokens frequently and monitor for leaks.

Monitor Risk Continuously - As supply chains evolve, keep checking for new threats.

Contain Compromises - Have plans to isolate third parties in case of a breach.

Incorporate M&A Attack Surface - As you acquire companies, quickly onboard new assets into your EASM program.

Proactively managing third party driven external risk is necessary for robust cyber resilience.

Implementing a Vulnerability Disclosure Program

Vulnerability disclosure or bug bounty programs provide an ethical way to identify blindspots in your external attack surface.

Key steps for implementing an effective vulnerability disclosure program:

Publish Disclosure Policy - Provide clear guidelines on scoping, rewards, and researcher interactions.

Define Scope - Specify which assets are in scope for testing based on criticality.

Establish Rewards - Compensate researchers proportional to vulnerability severity.

Alert Monitoring Team - Ensure security staff are prepared to handle submissions.

Triage Issues - Reproduce reports, determine severity level, and formulate remediation.

Remediate - Resolve confirmed vulnerabilities and implement new controls to prevent recurrence.

Improve Secure Development - Feed bug data back into SLDC processes.

Recognize Researchers - Publicly acknowledge those who ethically disclosed issues.

Expand Scope - Gradually allow testing on more assets once program matures.

Handled well, bug bounties provide valuable continuous monitoring of your evolving external attack surface.

Creating an Incident Response Plan

Despite your best efforts at proactive management, external threats can sometimes translate into security incidents that require swift response. Here are some key considerations for external attack surface incident response:

Have an action plan for various breach scenarios ready for activation.
Establish owners and playbooks for managing threats in each external environment - cloud, web, remote access, etc.
Designate emergency contacts at third parties for prompt notification and cooperation.
Prepare crisis communications for updating customers, employees, shareholders, and the public.
Ensure you have adequate forensic capabilities for gathering evidence about the nature and scope of incursion.
Be ready to bring on supplemental capacity and expertise if required - cyber insurance may help.
Determine criteria for deciding between isolating or evacuating compromised environments.
Develop procedures for controls, like firewall rules or API key rotation, to contain threats.
Archive incident data for future response playbook improvements and compliance audits.

Having robust incident response protocols tailored to your external attack surface will help you react quickly and minimize damage.

Measuring the ROI of EASM

Like any major security investment, implementing an external attack surface management program requires budget. Being able to measure and demonstrate a quantifiable return on investment is key to justifying and expanding EASM capabilities.

Some tips for tracking EASM ROI:

Establish KPIs based on risk reduction over time as vulnerabilities are remediated.
Calculate the potential losses avoided by proactively identifying and closing security gaps.
Weigh the costs of fines avoided and brand damage prevented.
Factor in IT and SecOps productivity gains from workflow automation.
Compare costs versus traditional perimeter monitoring and manual red team testing.
Highlight improved regulatory audit performance.
Show reductions in dwell time and containment costs for incidents originating externally.
Correlate with data on decreased malware and ransomware attacks.
Measure third party risk management improvements.

Quantifying EASM benefits empirically makes a much stronger case than hypothetical projections.

Conclusion

In today's hyperconnected business environment, the external attack surface represents one of the most significant cyber risk areas. As the renowned security researcher Ken Thompson succinctly states: "You can't trust code that you did not totally create yourself."

The expanding reliance on third parties means the code securing your systems and data sits largely out of view. By embracing continuous discovery, monitoring, and control of your external attack surface, you can meet this key challenge of modern cyber defense.

With a sound strategy based on automation, intelligence sharing, and cross-team coordination, you can master external attack surface management at scale. The ability to see into the shadows, assess risks in context, and rapidly remediate will help your organization thrive securely despite the growing complexity of cyberspace.

Summary of Key Recommendations

Achieve comprehensive visibility across your entire external attack surface.
Continuously monitor assets and access points for vulnerabilities.
Quantify risk context to prioritize remediation smartly.
Leverage automation to accelerate threat detection and response.
Collaborate with partners to reduce shared supply chain risk.
Implement a proactive vulnerability disclosure program.
Prepare incident response plans tailored to your external environments.
Track risk reduction metrics to measure EASM ROI.

With thoughtful strategy and robust tools, you can confidently manage your dynamic external attack surface. Mastering EASM is imperative for cyber resilience.