External Attack Surface Management (EASM): The Complete Starter Guide

What is External Attack Surface Management?

EASM is the process of discovering, validating, prioritizing, and remediating exploitable vulnerabilities in Internet-facing systems. Examples of sources of weaknesses that make up an external attack surface include:

• Cloud infrastructures: Attackers can exploit misconfigured cloud storage – that’s problem number one when it comes to cloud security, according to NSA. They also can leverage weak access controls, or gaps in shared security responsibilities to compromise sensitive data or gain unauthorized access to cloud resources.
• Websites and web applications: Threat actors can exploit site and application vulnerabilities through input validation, SQL injection, or XSS to gain unauthorized access to systems or compromise user data.
• APIs: As communication bridges between applications, APIs are prime attack targets. Vulnerabilities in APIs include weak authentication mechanisms, inadequate input validation, and insecure endpoints.

All these may seem like a handful, but EASM aims to reduce the number of potential attack entry points in external-facing systems to prevent threat actors from breaching an organization’s digital infrastructure.

What Contributes to Your External Attack Surface?

An organization’s external attack surface is the full scope of its digital assets accessible via the Internet and the attack vectors associated with them. Over time, this surface keeps growing due to digital transformation, interconnectivity, and cloud migration.

Enterprises take on more assets from inevitable business processes and expansions. And the more external assets an organization has, the more attack vectors threat actors can abuse.

Human error is also a significant contributor to an organization’s attack surface. Employees may set up misconfigured domains, subdomains, email inboxes, cloud services, and other assets or fail to decommission those they no longer use. Either way, these shadow IT assets can turn into weak spots that malicious actors may try to exploit.

Taking control of shadow IT and reducing your external attack surface is much easier with an EASM platform. Use Attaxion – the EASM platform that can discover more assets than any other – to get a bird’s eye view of your external attack surface, prioritize patching vulnerabilities, and plan remediation.

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How Does External Attack Surface Management Differ from Attack Surface Management?

While EASM is a crucial part of the broader attack surface management (ASM) process, the two should not be confused. In fact, ASM consists of three parts:

• EASM (external attack surface management);
• CAASM (cyber asset attack surface management);
• DRPS (digital risk protection services).

Below are some of the differentiating factors between EASM and ASM.

• Asset discovery scope: EASM focuses on external-facing assets accessible from outside an organization’s network, such as websites, web applications, and APIs. ASM, meanwhile, deals with both internal and external assets. Because internal systems can only be accessed from inside a network, such as employee portals and physical access points like server rooms, employee entrances, and data centers, they require different tools such as CAASM for analysis. 
• Perspective: EASM looks at a digital infrastructure from an external attackers’ perspective. By looking from the outside in, it aims to see how threat actors can exploit vulnerabilities and gain unauthorized access. Meanwhile, CAASM looks at the asset from the inside out, assuming the blue team’s perspective. Both EASM and CAASM are important parts of ASM, which considers potential risks from all sources, including insider threats, external attackers, and supply chain vulnerabilities. 
• Implementation: EASM involves using specialized tools and platforms designed to scan and assess an organization’s external-facing resources. Thanks to the outside-in approach, EASM platforms are easy to set up, don’t require a lot of integrations, and are heavily automated. In contrast, ASM typically requires a combination of tools (for EASM, CAASM, and DRPS) and processes like employee training to prevent social engineering attacks as part of managing one’s overall attack surface holistically. CAASM relies much more on manually executed tasks and API integrations with data sources to gather information, which makes the setup of CAASM platforms more complicated than in the case of EASM.

Related materials

• Asset Inventory Management
• Risk-Based Vulnerability Management

How Does External Attack Surface Management Work?

EASM is a cyclical process that starts with attack surface discovery, followed by vulnerability prioritization, remediation, and continuous monitoring. These phases utilize a combination of automated and manual operations described in greater detail below.

Step #1: Attack Surface Discovery

Attack surface discovery consists of three main processes — external asset enumeration, asset validation, and vulnerability detection. The first step in EASM is to catalog all Internet-facing assets, which may include:

• IP addresses
• Domain names
• Subdomains
• Ports
• SSL certificates

In this phase, EASM platforms use modern reconnaissance techniques similar to known attacker methods to surveil an organization’s external infrastructure.

After building a complete asset inventory, the next step is validating assets to ensure they are attributable to a target organization. That is doable through rule-based heuristics, ML algorithm usage, and other contextualization techniques. Asset validation is crucial in building an accurate external asset inventory with as few false positives as possible.

The last step of attack surface discovery is vulnerability detection, where the EASM platform scans all attributable assets to search for issues, misconfigurations, and other vulnerabilities. Domain names, for example, are scanned to check if their DNS records are configured correctly. IP addresses and linked connected servers, meanwhile, are checked for suboptimal cipher suites, among other weaknesses.

All assets are tested for new and emerging CVEs. EASM platforms rely on collecting data about new vulnerabilities from various sources – from CERT (Computer Emergency Response Team) portals of various organizations to crowdsourced directories. The vulnerable assets and the vulnerabilities discovered make up an organization’s external attack surface.

Step #2: Vulnerability Prioritization

Not all vulnerabilities pose the same level of risk. As such, accurate prioritization through risk scoring is a must to address the most critical issues first. That way, teams can efficiently focus their efforts on the bugs that matter most.

Vulnerability scoring can be done automatically based on the following criteria:

• Severity: The importance of each affected asset and the amount of damage the vulnerability can cause. This is usually measured using CVSS (Common Vulnerability Scoring System) score on a scale from 0 to 10, where 10 is the CVSS score of the most critical vulnerabilities.
• Exploitability: The ease at which attackers can exploit the vulnerability. This is measured using EPSS (Exploit Prediction Scoring System) score that’s calculated based on exploit availability and complexity, asset exposure, and other parameters. EPSS has a scale from 0 to 1 where 1 is highest likelihood of exploitation.
• Relevance: The likelihood that the organization would be targeted by malicious actors.

Intelligent EASM platforms consider all these factors while allowing for customization. Security teams can fine-tune risk scoring to align with their security policies, and the platform adjusts its algorithm based on this organizational context.

Risk-based vulnerability management takes into account the business context of an asset in addition to the three criteria listed above. The higher the business criticality of an asset, the more severe the impact of potential security incidents, and the higher the priority given to the associated cyber risks.

Step #3: Vulnerability Remediation

At this point, security teams devise remediation plans to address high-priority vulnerabilities and implement these with the EASM platform’s help. Team leaders can assign, track, and close tasks within the platform, fostering collaboration and expediting remediation for faster attack surface reduction.

With organizations often requiring days to resolve a security issue, automated remediation workflows are crucial in reducing the MTTR (mean time to resolution).

Step #4: Continuous Attack Surface Monitoring

Even as organizations eliminate attack vectors, new ones get added over the course of business operations, especially those involving digital transformation, cloud migration, and M&As.

As such, continuous visibility across one’s real-time external attack surface is necessary. EASM platforms usually do that by continually discovering, validating, and scanning new assets for existing and emerging vulnerabilities.

How Do Various Industries Use External Attack Surface Management?

Regardless of industry, all entities strive to better manage their own external attack surfaces. Aside from the overarching goal of protecting systems from external threats, EASM helps organizations address industry-specific challenges. Here are some ways EASM can help in various industries.

Government Agencies

The government sector is heavily targeted by sophisticated threat actors. That highlights the importance of reducing each entity’s external attack surface through deeper visibility and insights that supplement existing foreign, military, and global threat intelligence sources.

By uncovering and remediating vulnerabilities in mission-critical external assets, government agencies and departments can:

• Manage their nation’s threat exposure
• Fight against APTs
• Comply with federal security frameworks and regulations

Financial Organizations

With scattered and multiple digital touchpoints, financial institutions have so much external attack surface to cover. Gaining complete and up-to-date visibility over all Internet-facing assets through EASM enables them to:

• Protect sensitive financial client data
• Prevent financially motivated attacks
• Comply with cybersecurity laws applicable to their industry

Aside from banks and investment companies, cyber insurance companies can also make accurate and well-informed underwriting decisions with EASM’s help.

Online Marketplaces

E-commerce companies, API marketplaces, and other online retail platforms need help to provide customers with a safe environment as they increasingly rely on cloud-based systems, API integrations, and other external-facing technologies.

Online businesses need to proactively identify and protect known, unknown, and new assets. EASM helps them accomplish that by providing complete attack surface visibility that enables them to:

• Secure customer payment information
• Protect their brand reputation
• Reduce cloud-based risks
• Comply with e-commerce and data privacy laws

IT and Software Companies

Security gaps are inevitable, especially for companies that develop new applications and software. The key is to detect blind spots before attackers can. EASM allows AppSec and ProdSec teams to see their external IT and cloud assets in one place with as little noise and few false positives as possible, enabling them to:

• Quickly detect security gaps like asset misconfigurations and unsecured applications
• Customize risk scoring so they can focus on the most critical and relevant risks first
• Remediate vulnerabilities seamlessly

Healthcare Organizations

Healthcare organizations increasingly rely on connected IT systems and the cloud, which exposes them to several risks, including patient data breaches, ransomware attacks, and denial-of-service attacks. EASM can help these organizations efficiently manage risks by:

• Providing a complete and real-time catalog of all external-facing assets comprising their large digital operations and cloud environments
• Allowing limited security personnel to view, rank, and remediate vulnerabilities in one place
• Continuously detecting new assets and vulnerabilities that could expose electronic protected health information (ePHI) to ransomware and other attacks.

How Can Attaxion Help with External Attack Surface Management?

Attaxion is an EASM platform that provides organizations with the broadest yet highly meaningful asset discovery coverage, allowing them to map out their entire external attack surfaces in real time. We use patent-pending reconnaissance techniques, rule-based heuristics, and ML-powered engines to identify, validate, and prioritize assets accurately.

Automated remediation workflows integrated into the most popular communication platforms allow for seamless collaboration that facilitates quick vulnerability remediation and ultimately expedites attack surface reduction.

Ready to see Attaxion in action? Schedule a customized demo now.

Learn More

• What Is Attack Surface Analysis?
• How Are Attack Vectors and Attack Surfaces Related?

Frequently Asked Questions

What Is an External Attack Surface?

An external attack surface encompasses an organization’s Internet-facing digital assets and their associated attack vectors. Such surfaces tend to expand as a result of day-to-day operations and expansions (e.g., new product launches, mergers and acquisitions, etc.). As the organization takes on more external digital assets, more potential attack vectors emerge.

What Are Examples of External Attack Surfaces?

External attack surfaces have become more common as organizations increasingly conduct business over the Internet. The bigger their digital footprint, the larger their external attack surface becomes. Examples of external attack surface contributors include:

• Websites and web applications
• Insecure ports
• Misconfigured DNS records
• Cloud infrastructure
• Third-party applications

External attack surface management solutions can provide visibility over external attack surfaces, along with the connections between and the assets within them.

What Are Examples of External Attack Surface Management Techniques?

EASM techniques include:

• Automated asset scanning: EASM platforms systematically scan the Internet and connected systems to identify all public-facing assets, including websites, subdomains, IP addresses, ports, and cloud resources.

• API discovery and analysis: EASM platforms map externally exposed APIs, assess their security posture, and identify potential vulnerabilities.

• Shadow IT detection: EASM platforms have the capability to uncover unauthorized or undocumented assets outside the oversight of the IT team (known as Shadow IT) and which thus very likely pose great security risks.

• Web application scanning: EASM platforms crawl and analyze websites and web applications to identify misconfigurations and vulnerabilities, including those found in MITRE’s Common Vulnerabilities and Exposures (CVE) list.

• Threat intelligence analysis: Leveraging external threat feeds helps EASM platforms prioritize vulnerabilities based on known exploits and attacker patterns.

What Is the Difference between External Attack Surface Management and Vulnerability Management?

EASM and vulnerability management are crucial cybersecurity processes that enable organizations to identify and address vulnerabilities to prevent attackers from exploiting them. However, EASM has a broader scope and encompasses vulnerability management. Specifically, the two processes differ in these aspects:

• Focus: EASM covers an organization’s entire Internet-facing digital infrastructure, including known, forgotten, and unknown assets. Vulnerability management has a narrower focus since it primarily zooms in on vulnerabilities within known assets only.

• Scope: The overall EASM process begins with external asset discovery, where the platform identifies all exposed assets, including those outside the current IT inventory. On the other hand, vulnerability management relies on an existing asset inventory and starts by scanning known assets for weaknesses.

• Analysis: EASM analyzes the external attack surface as a whole, taking into consideration the relationships between assets and the potential impact of security issues found. Vulnerability management analyzes each asset individually and prioritizes patching based on severity and exploitability.

• Outcome: EASM aims to reduce the overall attack surface by minimizing exposure, hardening configurations, and mitigating external risks. Vulnerability management focuses on remediating vulnerabilities within identified assets to prevent exploitation and data breaches.

EASM provides context and help with prioritization for vulnerability management efforts by identifying the most critical assets and weaknesses.

What Is the Difference between Internal and External Attack Surfaces in Cybersecurity?

Internal and external attack surfaces are the two parts of an organization’s digital attack surface. While both encompass vulnerable digital assets and vulnerabilities, there are significant differences between them.

Only Internet-facing assets contribute to the external attack surface. On the other hand, only assets within the corporate network infrastructure contribute to the internal attack surface. The entry points of cyberattacks belong to external attack surfaces. Attackers leverage internal attack surfaces to traverse the network after the initial penetration (something known as lateral movement).

As a result, the means of protection are also very different. For protecting their external attack surfaces, corporations rely on EASM tools that have an outside-in approach, looking at the organization’s external assets from the same perspective an attacker would.

That approach doesn’t work with internal assets, as they are not directly accessible via the Internet, so the tools corporations use for protecting internal attack surfaces (such as CAASM) have an inside out approach.

What Is the Difference between External Attack Surface Management and Cyber Asset Attack Surface Management?

Both EASM and cyber asset attack surface management (CAASM) deal with managing an organization’s attack surface, but they differ in scope, data sources, and approach.

• Scope: EASM focuses solely on an organization’s external attack surface, encompassing all Internet-facing assets like websites, APIs, cloud resources, and exposed vulnerabilities. CAASM covers both internal and external assets, including servers, devices, applications, user accounts within a network, and their external components.

• Data sources: EASM relies on external data sources like Internet scans, vulnerability databases, and threat intelligence feeds to discover and analyze assets. CAASM leverages internal data sources, such as asset inventories, security tools, and endpoint management systems, to identify and assess assets. For additional context, CAASM may also rely on external data sources, including EASM platforms.

• Approach: EASM primarily focuses on attack vectors and vulnerabilities associated with external assets, prioritizing risks based on their potential impact. Meanwhile, CAASM provides a holistic view of the entire attack surface, considering relationships between internal and external assets, user behaviors, and potential insider threats.

CAASM can be seen as an extension of EASM. EASM platforms can complement CAASM by providing specialized insights into external threats and attack vectors.

What Is the Difference between External Attack Surface Management and Digital Risk Protection Services?

EASM and digital risk protection services (DRPS) play crucial roles in cybersecurity, but they take different approaches to safeguarding an organization.

EASM is a proactive approach to minimizing technical vulnerabilities in the external attack surface. It identifies and prioritizes weaknesses in Internet-facing assets like websites, APIs, and cloud resources to prevent exploitation.

Meanwhile, DRPS is a reactive approach that focuses on monitoring and mitigating reputational and brand risks stemming from digital data exposure. It proactively searches for sensitive information leakage and brand mentions across the Internet, including dark web forums and social media, to prevent or respond to data breaches and reputational damage.

EASM and DRPS are complementary security solutions. EASM actively minimizes vulnerabilities, while DRPS monitors for data breaches and branding-related threats arising from successful attacks or even human error.

Moreover, DRPS can inform EASM’s vulnerability prioritization phase. Information about exposed data or targeted attacks identified by DRPS can help organizations prioritize patching specific vulnerabilities discovered in EASM.