Security & Compliance · Engineering, IT & AI
Should you build or buy External Attack Surface Management (EASM)?
External Attack Surface Management (EASM) software continuously discovers and monitors all internet-facing assets associated with an organization — domains, IP ranges, cloud resources, certificates, subsidiaries, and exposed services — to give security teams visibility into what attackers see from the outside. It uses global internet scanning infrastructure, certificate transparency feeds, and passive DNS data to surface assets the organization may not know it owns.
The build-vs-buy decision for External Attack Surface Management turns on whether your team has the internet scanning infrastructure to discover assets you don't already know about versus relying on vendors who operate that data corpus at global scale; the specifics of your asset footprint complexity and subsidiary structure decide it.
Build it, buy it, or bridge?
When building makes sense
The build case for EASM is effectively limited to organizations that already operate significant internet scanning infrastructure for separate threat intelligence purposes — large financial institutions, defense contractors, or intelligence-affiliated organizations where running global passive DNS collection and IPv4 sweep scanning is already justified by other programs. For those organizations, extending existing infrastructure to cover attack surface discovery is incremental work rather than a new investment. Everyone else is looking at a build cost that exceeds vendor 3-year TCO before getting to the data corpus problem: the value of EASM isn't the alerting logic, it's the billions of records of internet-wide scan data that vendors accumulate continuously. You can't solve that with a well-designed scanning script.
When buying makes sense
Buying is the right call for nearly any organization that wants to understand its external exposure from an attacker's perspective. Censys ASM and Palo Alto Cortex Xpanse operate continuous global internet scans, certificate transparency feeds, and cloud asset enumeration at a scale that requires infrastructure investment no single organization's security program would fund independently. The core question EASM answers — what does the internet see about our organization that we don't know about — is inherently a cross-internet-data problem. Subsidiary discovery and cloud asset proliferation are making the question harder to answer over time, not easier. Detectify's approach to web application exposure and CyCognito's automated attack path analysis represent meaningfully different methodologies for the same discovery goal, and vendor selection should match the complexity of your asset footprint.
The desk read
EASM is grounded in data infrastructure that no single organization can build. Vendors like Censys ASM and Palo Alto Cortex Xpanse operate continuous global internet scans, passive DNS aggregation, certificate transparency feeds, and cloud asset enumeration at a scale that requires dedicated infrastructure investment far beyond what any internal team would fund. Buying earns its keep when the primary question is: what does the internet see about our organization that we don't know about? The answer requires a corpus of data that only vendors collecting across the full internet can provide.
The build case is essentially limited to organizations with existing threat intelligence infrastructure, typically large financial institutions or defense contractors already running their own scanning operations for other reasons. For most teams, the decision isn't build-vs-buy but which vendor's discovery methodology best handles your specific footprint, particularly as cloud asset proliferation and subsidiary discovery become more complex. Detectify's focus on web application exposure and CyCognito's automated attack path mapping represent meaningfully different approaches to the same problem.
Vendors in External Attack Surface Management (EASM)
Each file covers what the product is, its funding history, and when the index last verified it alive.
Frequently asked
What is External Attack Surface Management (EASM)?
External Attack Surface Management software continuously discovers and monitors all internet-facing assets associated with an organization — domains, cloud resources, exposed services, subsidiaries — to give security teams visibility into what attackers see from the outside. It uses global internet scanning data and passive DNS aggregation to surface assets the organization may not know it owns.
When does building External Attack Surface Management make sense?
Building is realistic only for organizations with existing global internet scanning infrastructure — large financial institutions or defense contractors where that investment is already justified by other threat intelligence programs. For everyone else, the data corpus required to discover unknown assets can't be assembled from internal scanning alone.
When does buying External Attack Surface Management make sense?
Buying is the right call for nearly any organization that wants external attacker visibility without building global scanning infrastructure. Vendors like Censys ASM and Palo Alto Cortex Xpanse operate the data corpus at a scale that no single organization's security budget would fund, and subsidiary discovery complexity is growing, not shrinking.
What are the main External Attack Surface Management (EASM) vendors?
Representative vendors include Censys ASM, Detectify, Tenable Attack Surface Management, Palo Alto Networks Cortex Xpanse. B4 Pro scores the full set.