Why do mergers and acquisitions increase IAM and NHI risk so quickly?

Why This Matters for Security Teams

Mergers and acquisitions compress years of identity sprawl into a single transition window. Human accounts, service principals, API keys, certificates, and shared secrets all need to be inventoried, mapped, and re-authorised while business teams expect continuity. That is why identity risk rises so quickly: governance is usually slower than integration. NHI Management Group research in the 2024 Non-Human Identity Security Report found that 88.5% of organisations say non-human IAM lags behind or only matches human IAM, which is a major warning sign during deal close and post-close integration. The same pattern shows up in broader NHI guidance such as Top 10 NHI Issues, where unmanaged trust relationships and weak secret handling repeatedly surface as core failures. Security teams often assume the main task is merging directories, but the real issue is reconciling authority, not just accounts. In practice, many security teams encounter excessive access only after shared credentials and legacy integrations have already crossed environment boundaries.

How It Works in Practice

The fastest way to reduce M&A identity risk is to treat the integration as an active privilege containment exercise, not a back-office sync project. Start by building an inventory of all identities that can authenticate, call tools, or trigger automation in both organisations. That includes workforce accounts, service accounts, CI/CD tokens, cloud roles, secrets stored in vaults, and any machine-to-machine trust created for the transaction. The goal is to identify what exists, what is still needed, and what can be removed or forced into NIST Cybersecurity Framework 2.0 governance processes.

Practically, that means applying temporary controls before full consolidation:

• Shorten credential lifetime and replace static shared secrets with just-in-time issuance where possible.
• Segment inherited trust so the acquired environment does not automatically inherit broad parent-company permissions.
• Re-validate high-risk access paths for administrators, automation pipelines, and third-party integrations.
• Use workload identity for services and agents instead of copying long-lived secrets into the new estate.

For NHIs specifically, the most common failure is assuming that a service account behaves like a human account. It does not. It may be embedded in automation, reused across pipelines, or silently depended on by multiple applications. NHI Management Group’s Ultimate Guide to NHIs highlights why these identities are hard to centralise: they are often undocumented, over-privileged, and operationally fragile. The right pattern is to move toward policy-driven access decisions, ephemeral credentials, and explicit ownership for every workload identity, then align those identities to the post-merger operating model rather than the pre-merger one. These controls tend to break down when both organisations share infrastructure during a phased cutover because inherited trust chains become too complex to validate in real time.

Common Variations and Edge Cases

Tighter identity controls often increase integration time and operational overhead, so organisations have to balance speed against containment. That tradeoff is especially sharp in regulated sectors, where a rushed acquisition can leave dormant accounts, duplicated privileges, and overlapping secret stores in place for months.

One common edge case is a partial carve-out, where only part of the acquired business migrates. In that model, the surviving enclave may need temporary cross-domain access, but current guidance suggests those exceptions should be narrowly scoped, time-bound, and reviewed continuously. Another problem is vendor or SaaS sprawl: if the target company has dozens of external integrations, revoking access too aggressively can break billing, support, or production workflows. Best practice is evolving, but the safest approach is to classify every identity by business criticality and expiry date, then enforce an explicit owner for each exception.

NHIMG’s 52 NHI Breaches Analysis and Cisco DevHub NHI breach both reflect a recurring lesson: the most damaging exposures are often not the most visible ones, but the overlooked machine identities and shared trust paths that survive transition. When that environment also includes weak secret hygiene, the risk compounds quickly. Organisations that delay identity rationalisation until after systems are merged usually discover the worst access paths only during incident response, not during planned diligence.

Related resources from NHI Mgmt Group

• Why do Salesforce integrations increase NHI risk?
• Why do mergers and acquisitions increase privileged access risk so quickly?
• Why do mergers and acquisitions create IAM risk so quickly?
• Why do leaked secrets remain such a persistent NHI risk?