Cybersecurity Due Diligence in M&A: What PE Firms Miss Before Close
By Dritan Saliovski
Cybersecurity due diligence in M&A transactions has matured significantly over the past decade. Most PE deal teams now include some form of cyber assessment in their process. The problem isn't whether it gets done; it's how.
Key Takeaways
- Self-reported questionnaires cannot surface vulnerabilities the target is unaware of, legacy system exposure, or credentials already circulating from prior breaches
- External intelligence, requiring no target access, consistently identifies material issues that traditional reviews miss until post-close
- In competitive processes where system access is restricted or unavailable, an external-first approach is the only viable option from day one
The questionnaire trap
The default approach relies on target-completed questionnaires and a limited number of stakeholder interviews. This has a structural flaw: the information is entirely self-reported, and limited to what the target knows about itself.
Most organizations have significant blind spots in their own security posture. Legacy systems accumulate vulnerabilities that were never catalogued. Integrations added outside formal IT processes go undocumented. Credentials remain active long after employees leave. These don't appear in a well-formatted response to a 200-question spreadsheet, not because they are withheld, but because the target often isn't aware of them either.
What external intelligence reveals
A properly structured external assessment, conducted without any target access, can identify issues that self-reported questionnaires systematically miss:
| Assessment area | What questionnaires miss | What external intelligence finds |
|---|---|---|
| Infrastructure vulnerabilities | Self-reported; depends on target's own awareness | Open ports, misconfigured cloud storage, and unpatched systems via passive scanning |
| Credential exposure | Not visible to the target; cannot be self-reported | Email and password combinations from prior breaches circulating on dark web forums |
| Third-party dependencies | Incomplete; limited to what target actively tracks | Vendors and integrations mapped externally, including untracked or shadow IT |
| Historical incidents | Limited to what the target has formally recorded | Public breach disclosures, regulatory filings, and litigation records |
| Technology stack | Claimed by target | Independently verified against job postings, DNS records, and open-source signals |
| Access required | Yes, limiting competitive processes | No, assessment runs from day one without notifying the company |
This isn't theoretical. In transaction after transaction, external intelligence surfaces material issues that traditional access-based reviews miss until post-close, when remediation costs have already been absorbed by the acquirer.
The access problem
Traditional due diligence requires the target to grant meaningful system access. In competitive processes, this is often unavailable or restricted. In add-on acquisitions, the access request itself signals sensitivity that deal teams prefer to avoid.
An external-first approach removes this constraint entirely. Assessment begins the moment a target is identified, without notifying the company, without requesting access, and without consuming management bandwidth.
What to look for in a cyber DD provider
| Capability | Why it matters for deal teams |
|---|---|
| Initial risk profile before first target conversation | Enables early go/no-go signalling before committing full DD resources |
| Independent technology stack verification | Validates what the target claims is actually in production |
| Full audit trail on all findings | Defensible to co-investors, LPs, and regulatory scrutiny under DORA and NIS2 |
| Findings translated to financial exposure | Connects technical risk to deal economics and SPA representations |
For the complete assessment methodology, see our practitioner's framework for M&A cybersecurity due diligence. For how findings translate into deal economics, see how cybersecurity due diligence protects deal value. For rapid assessment in competitive processes, see digital due diligence in 24-72 hours.
The checklist covers the key assessment domains we apply across every transaction, from initial screening through binding offer.
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Request M&A Cyber Due Diligence ChecklistFrequently Asked Questions
Why do standard cybersecurity questionnaires fail in M&A due diligence?
Self-reported questionnaires are limited to what a target organization knows about itself - and most organizations have significant blind spots in their own security posture. Legacy systems accumulate vulnerabilities that were never catalogued, integrations added outside formal IT processes go undocumented, and credentials can remain active long after employees leave. These gaps do not appear in questionnaire responses not because they are withheld, but because the target is often unaware of them.
What does external-only cybersecurity assessment reveal that questionnaires miss?
External assessment without any target access identifies open ports and misconfigured cloud storage via passive scanning, email and password combinations from prior breaches circulating on dark web forums, vendors and integrations (including shadow IT) mapped from external signals, public breach disclosures and regulatory filing history, and independently verified technology stack details - all of which self-reporting systematically cannot surface.
How can PE deal teams assess cybersecurity risk before gaining access to target systems?
External-first assessment draws on 500+ data sources covering cybersecurity, technology stack, and regulatory history without requiring system access, management cooperation, or even notifying the target. Assessment begins from the moment a target is identified - in competitive processes, this means having independent technical intelligence before management representations are made, without consuming deal timeline.
Related Insights
Sources
- OWASP - Web Security Testing Guide
- Have I Been Pwned - Breach Database and Credential Exposure
- NIST. National Vulnerability Database. nist.gov. 2025.