James Griffiths – UtopianKnight

Cyber & Information Security Blog – Written with the help of AI (ish)

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Understanding External Attack Surface Management (EASM): What It Is and Why Your Business Needs It

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Organisations increasingly rely on a vast and growing ecosystem of internet-facing assets web servers, APIs, cloud services, mobile apps, and more. While these technologies offer incredible agility and scalability, they also expand what cybersecurity experts refer to as the “attack surface.”

External Attack Surface Management (EASM) is a rapidly emerging security discipline aimed at identifying, monitoring, and securing all of an organisation’s externally visible assets. In this article, we’ll explore what EASM is, why it’s critical, how it works, and which leading vendors offer the best solutions.


What is External Attack Surface Management (EASM)?

EASM is the process of continuously discovering and assessing the risks of an organisation’s exposed digital infrastructure. Unlike traditional vulnerability management which typically focuses on known, internally tracked systems EASM operates from the outside-in, just like a hacker would.

Think of EASM as your organisation’s digital reconnaissance tool. It helps identify:

  • Unknown or forgotten assets (“shadow IT”)
  • Misconfigured cloud services
  • Unpatched web applications
  • Exposed development environments
  • Leaked credentials or API keys
  • Outdated DNS records or domains

These are all potential entry points for cybercriminals. EASM aims to provide security teams with continuous visibility of their digital perimeter so they can detect risks before they are exploited.


Why EASM Matters

1. Shadow IT and Asset Sprawl

As organisations move faster with agile development, cloud migrations, and remote workforces, it’s easy for systems to be deployed without the knowledge of IT or security. EASM uncovers these hidden systems before attackers do.

2. Growing Use of SaaS and Cloud

Modern businesses depend heavily on third-party platforms and services. EASM tools identify and track the growing list of dependencies and public-facing APIs, which are commonly targeted in attacks.

3. Real-World Attacker Perspective

By emulating the reconnaissance phase of a cyberattack, EASM provides a realistic assessment of your exposure; what an attacker sees is what your security team sees.

4. Risk Reduction and Compliance

EASM helps reduce the likelihood of data breaches and supports compliance with standards like ISO 27001, PCI DSS, and NIS2, which mandate strong visibility into external systems.


How EASM Works

A typical EASM solution includes:

1. Asset Discovery

Automated scans across IP ranges, domains, subdomains, and third-party platforms. Some tools use OSINT (Open Source Intelligence) and DNS enumeration to uncover assets.

2. Asset Attribution

Not every domain or service that mentions your brand belongs to you. EASM tools use context, certificate chains, and behavioural signatures to determine asset ownership.

3. Risk Assessment

Once assets are mapped, they are scanned for vulnerabilities, misconfigurations, exposed services, and outdated software.

4. Monitoring and Alerts

EASM platforms continuously monitor changes in the attack surface and alert teams when new assets or risks are discovered.

5. Integration with Security Workflows

Many EASM tools integrate with SIEM, SOAR, and ticketing systems to enable rapid triage and remediation.


Use Cases for Businesses

Digital Risk Discovery

Gain visibility into all external assets; known and unknown.

Third-Party Risk Management

Monitor the external assets of suppliers or partners as part of your third-party risk assessments.

M&A Due Diligence

Assess the external cyber hygiene of a potential acquisition target.

Brand Protection

Detect and shut down spoofed domains or phishing infrastructure that abuses your brand.

Incident Response Readiness

Speed up response time by having a pre-mapped view of what attackers can access.


Top 5 Vendors in EASM

Here are five of the leading vendors in the EASM space, known for their innovation, scale, and ease of integration:


1. Microsoft Defender External Attack Surface Management

Microsoft’s EASM solution is part of the Defender for Threat Intelligence suite. It integrates well with Microsoft Defender XDR and offers strong asset discovery using internet-wide scanning and passive DNS telemetry.

🔗 https://www.microsoft.com/en-us/security/business/threat-protection/microsoft-defender-external-attack-surface-management


2. Palo Alto Networks – Cortex Xpanse

Xpanse is a market leader in attack surface discovery and monitoring. It uses large-scale internet scanning to continuously map assets globally and provides rich context for each discovery.

🔗 https://www.paloaltonetworks.com/cortex/cortex-xpanse


3. SecurityScorecard

Best known for vendor risk ratings, SecurityScorecard also offers powerful EASM capabilities that help organisations discover unknown assets, analyse risk posture, and share security ratings with stakeholders.

🔗 https://securityscorecard.com/products/attack-surface-management


4. CyCognito

CyCognito provides a highly automated platform that specialises in identifying and contextualising risky assets. It’s particularly strong at identifying shadow IT and correlating assets to business units.

🔗 https://www.cycognito.com


5. Randori (an IBM Company)

Randori offers a unique EASM solution with attack simulation built in. It continuously maps the attack surface and prioritises risks based on how an actual adversary would exploit them.

🔗 https://www.randori.com


Final Thoughts

External Attack Surface Management is no longer a niche capability; it’s quickly becoming a foundational component of modern cybersecurity. With cyber threats growing in both volume and sophistication, organisations must gain visibility and control over every external-facing system they operate.

Whether you’re a small business or a multinational enterprise, EASM helps you stay one step ahead of attackers by continuously showing you what they see.

By adopting a mature EASM strategy with support from the right vendor, your organisation can reduce cyber risk, boost compliance readiness, and build resilience in an increasingly digital world.


Want to know how EASM fits into your cybersecurity roadmap or compliance programme? Reach out to our trusted security advisory team to start mapping your external attack surface today. https://csacyber.com