External attack surface management (EASM) is the continuous discovery, analysis and remediation of an organization’s internet-facing assets and exposures, such as forgotten subdomains, misconfigured cloud services, open ports and employee credentials leaked in other companies’ breaches. EASM prevents data leaks by finding these weak points and prioritizing fixes before attackers can exploit them.
Key Takeaways
- One company’s breach becomes another company’s risk because stolen passwords are reused in credential stuffing attacks.
- According to IBM’s Cost of a Data Breach Report 2026, the global average cost of a breach is $4.99 million, a record high.
- EASM works in a loop: discover internet-facing assets, analyze and prioritize exposures, then remediate and monitor again.
- EASM covers leaked credentials, cloud misconfigurations, shadow IT and the wider digital footprint of a business.
- Tools support, but do not replace, basic cyber hygiene: unique passwords, multi-factor authentication and fast patching.
In 2013, Yahoo suffered one of the worst data breaches known to this day. The August 2013 breach affected all three billion Yahoo user accounts and was not disclosed until December 2016. According to Wikipedia’s summary of the case, the stolen data included names, email addresses, phone numbers, birth dates, hashed passwords and security questions. Yahoo later agreed a $117.5 million class action settlement (April 2019), and its successor company Altaba paid a $35 million SEC fine in 2018 over the separate 2014 breach.
Today, a lot has changed.
There are stricter privacy laws and newer security tools to detect and limit compromised data, yet breaches keep getting more expensive. IBM’s Cost of a Data Breach Report 2026 puts the global average cost of a data breach at $4.99 million, a 12% increase over the previous year and a record high.
Regardless, new data breaches are headlining the news every day, and users are tired of hearing that their information has been compromised during hacking.
The problem is — the data that gets stolen in breaches doesn’t harm only the victimized company and its users. One hack leads to another, creating a domino effect for individuals and other businesses.
How does one company’s data breach compromise the future of another?
What role does external attack surface management have in the discovery of exposed information and in protecting businesses from future attacks?
The Danger of Leaked Employee Data Following a Breach
Once a company suffers a data breach, it can lead to the theft of information. Bad actors can use the stolen data either to demand ransom (in exchange for not sharing sensitive user data) or sell the data to other criminals.
The consequences depend on the attack and what kind of data was exposed during it. The worst-case scenario of a data breach is a hacker releasing the stolen information to the public.
Data leaked on the dark web sold on hacking forums, or left in data dumps is like a ticking time bomb waiting to go off. It could be hours, days or months until a criminal uses it to breach another company or harm users whose data has been leaked.
An employee could unknowingly be using their leaked password for both personal and business accounts. With their credentials exposed on a hacking forum or a data dump, threat actors could have access to both.
As a result, the credentials can enable criminals to:
- Get into the system of another company.
- Perform a successful phishing campaign (since they have more data).
- Steal the identity of an unsuspecting individual.
- Extort businesses and users.
Identity theft is possible if the sensitive data that has been leaked or sold includes information such as social security numbers, birthdays, addresses, credit card numbers, and names.
After the September 2022 Optus breach in Australia, which exposed personal data of up to 10 million current and former customers, one Melbourne family lost $40,000 following the identity theft. According to that report in The Age, the family suspected that data stolen in the breach was used to withdraw money from their bank account; the link to the Optus breach was suspected rather than proven.
Preventing Hacking With External Attack Surface Management
In cybersecurity, the attack surface refers to anything that a cybercriminal could exploit for online criminal activity – entry points such as poorly protected websites and flaws in the cloud. Over the years, the attack surface expands.
To keep up, security teams now also have to consider external attack surfaces — internet-facing assets such as leaked passwords.
With more cyberattacks occurring than ever before and complex infrastructures such as multi-cloud environments that have to be properly set and regularly managed, securing business and preventing data breaches is bound to become even more challenging than it is.
To keep up, companies use external attack surface management (EASM) – a continuous process, usually delivered as a software platform, that discovers an organization’s internet-facing assets and the vulnerabilities in them. It does so by repeating the process of scanning for information, conducting an analysis and mitigating the threat.
Most EASM platforms run automatically and continuously, reporting the latest findings on a dashboard for the security team to see. When it does, it also analyzes the data and lets teams know which weaknesses are high risk — or which flaws need to be patched before others.
Let’s say a bad actor releases sensitive user or client data on a hacking forum. An EASM or threat-intelligence service that monitors such sources can warn the security team, which can then reset the affected accounts and require users to choose new passwords.
Additional Capabilities of External Attack Surface Management
Ultimately, external attack surface management is more than a tool for identifying rogue data in hacking forums.
The tool also:
- Uncovers a trail of the digital footprint of a business (anything shared by the company or about the company online).
- Finds vulnerabilities such as errors in the configuration of the cloud (AKA cloud misconfigurations).
- Discovers the use of shadow IT within the organization (such as devices security teams aren’t aware are being used by employees for work).
Even more, many EASM products map their findings to the MITRE ATT&CK Framework knowledge base. MITRE describes ATT&CK as a globally accessible knowledge base of adversary tactics and techniques based on real-world observations, so mapping findings to it shows teams which known attack techniques an exposure could enable.
Protecting the Future of the Company With Cyber Hygiene
When it comes to cybersecurity, here are some of the things that we know for sure:
- The attack surfaces of businesses continue to grow — creating even more blind spots for teams.
- A data breach of one company could lead to the data breach of another company or stolen identities.
- Hackers will continue using exposed data to conduct further attacks and target individual users.
- Security has to be updated at all times to keep up with the ever-shifting and ever-growing attack surface.
It’s important to uncover weaknesses such as leaked data or incorrectly configured cloud to repair such mistakes – patch up security and alter passwords before the hackers connect the dots and use them to damage your business.
The most security teams can do in such hectic times is to identify flaws and retain visibility of the attack surface with automated tools.
Regular management of security, updating devices, and discovering possible vulnerabilities is essential cybersecurity hygiene that can aid you in preventing hacking activity in the long run.
Data on the loose can turn your company into the next victim of a data breach — catch it with external attack surface management before hackers get the chance to exploit it.
What Is External Attack Surface Management?
External attack surface management is the practice of continuously finding, assessing and reducing everything an organization exposes to the internet. Wikipedia defines an attack surface as the sum of the points where an unauthorized user can try to enter data, extract data or control a system. The external part of that surface typically includes IP addresses, domain names and subdomains, SSL certificates, open ports and services, web servers and frameworks, and cloud infrastructure.
EASM looks at the organization the way an attacker does: from the outside, without internal credentials. That outside-in view is what catches assets the security team never knew existed, such as a test server left online or a marketing site hosted on an unmanaged cloud account.
How Does One Company’s Breach Put Another at Risk?
One company’s breach puts another at risk mainly through password reuse. Credential stuffing is an attack in which criminals take username and password pairs stolen in one breach and try them automatically on other services. Wikipedia’s article on credential stuffing cites research that 81% of users have reused a password across two or more sites, and notes that even a success rate of around 2% turns one million stolen credentials into roughly 20,000 compromised accounts.
The scale of the available data is large. As of October 2026, the breach notification service Have I Been Pwned lists more than 17.8 billion compromised email addresses from 1,041 breached websites. Any employee whose work email appears in that data, and who reused a password, is a potential entry point.
Verizon’s 2026 Data Breach Investigations Report, which covers incidents from November 2024 to October 2025, names stolen credentials, phishing and social engineering among the frequent causes of breaches, reports that exploitation of software vulnerabilities was the initial access vector in 31% of breaches, and found ransomware in 48% of all breaches.
EASM vs. Related Security Tools
| Approach | Main question it answers | Typical scope |
|---|---|---|
| External attack surface management (EASM) | What do we expose to the internet, and what is weak? | Domains, subdomains, IPs, certificates, cloud services, leaked credentials |
| Vulnerability scanning | Do known assets have known flaws? | Assets already listed in the inventory |
| Penetration testing | Can a skilled tester break in right now? | A defined target over a fixed test window |
| Threat intelligence and dark web monitoring | Is our data or brand being traded or discussed? | Hacking forums, paste sites, data dumps |
The key difference is discovery. A vulnerability scanner checks the assets it is told about; EASM is designed to find the assets nobody listed. Many organizations use the approaches together.
How to Prevent Data Leaks With EASM: A Step-by-Step Plan
- Build the inventory. Start with known domains, IP ranges and cloud accounts, then let discovery find related subdomains, certificates and hosts.
- Confirm ownership. Check that each discovered asset belongs to the organization, a subsidiary or a supplier, and assign an owner.
- Find exposures. Look for open ports, outdated software, expired certificates, cloud misconfigurations and employee credentials in breach data.
- Prioritize by risk. Fix internet-facing flaws that are known to be exploited, and exposed credentials, before cosmetic issues.
- Remediate. Patch, close unused services, take down forgotten assets and reset any account whose password appears in a breach.
- Monitor continuously. Repeat discovery on a schedule, because new assets and new leaks keep appearing.
Cyber Hygiene Steps That Make EASM Work
- Unique passwords: a password manager or a secure password generator stops one leak from unlocking several accounts. See also these ways to increase password management security.
- Multi-factor authentication: enabling it limits the value of a stolen password and is one of the standard countermeasures against credential stuffing.
- Breach monitoring: services such as Have I Been Pwned let individuals check an email address and let organizations monitor their corporate domains through an API.
- Staff awareness: leaked data often fuels targeted phishing, so training on how to protect employees from spear phishing scams closes a common follow-up attack.
- Cloud configuration reviews: misconfigured storage and services are a frequent source of exposure, as covered in this guide to the risk of data breaches in the cloud.
What to Do If Your Data Has Already Leaked
If company or personal data turns up in a breach, act on the exposed items first: change the affected passwords everywhere they were reused, turn on multi-factor authentication, warn the people involved about likely phishing, and watch bank and card statements for unfamiliar activity. Organizations should also check their legal duty to notify a regulator or customers in the relevant country. This guide on what to do if you are a victim of cybercrime covers reporting in more detail.
Frequently Asked Questions
What is the difference between ASM and EASM?
Attack surface management (ASM) covers every point an attacker could use, inside and outside the network. External attack surface management (EASM) focuses only on internet-facing assets and exposures, seen from an outsider’s point of view.
Can EASM find leaked passwords?
Many EASM and threat-intelligence services monitor breach data, hacking forums and paste sites for an organization’s domains and credentials. When a match appears, the security team can reset the affected accounts before attackers use them.
How much does a data breach cost?
According to IBM’s Cost of a Data Breach Report 2026, the global average cost of a data breach is $4.99 million, up 12% on the previous year. IBM also reports average savings of $1.93 million for organizations that use security AI and automation extensively, compared with those that use none.
How many accounts were affected by the Yahoo breach?
The August 2013 Yahoo breach affected all three billion user accounts. Yahoo disclosed it in December 2016, months after disclosing a separate 2014 breach of more than 500 million accounts.
Is EASM only for large companies?
No. Any organization with a website, email domain or cloud service has an external attack surface. Smaller businesses often start with a basic asset inventory, breach monitoring for their email domain and multi-factor authentication, then add an EASM platform as their footprint grows.
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