Why do mergers and acquisitions increase access risk for service accounts and privileged users?

M&A increases access risk because temporary exceptions become common, and temporary exceptions often survive longer than the integration itself. Service accounts, admin credentials, and shared access paths are especially exposed because they are less visible than human accounts and are often left out of early reconciliation work.

Why This Matters for Security Teams

Mergers and acquisitions create a high-risk identity window because the integration agenda usually moves faster than identity reconciliation. Human accounts get reviewed first, while service accounts, admin tokens, shared mailboxes, and break-glass credentials are often treated as background plumbing. That is precisely where excess access hides. NHI Management Group has documented that only 5.7% of organisations have full visibility into their service accounts in the Ultimate Guide to NHIs, which makes post-deal cleanup materially harder.

The problem is not only inherited access, but also the exception culture that appears during integration. Temporary trusts, delegated admin rights, and transitional automations are introduced to keep business operations running, then linger long after Day 1 or Day 100. Current guidance suggests treating these identities as active attack paths, not administrative leftovers. That perspective aligns with the OWASP Non-Human Identity Top 10 and the NIST view that identity governance must support continuous verification rather than periodic cleanup in the NIST Cybersecurity Framework 2.0.

In practice, many security teams discover excessive service-account access only after the first failed audit or the first post-close incident, rather than through intentional pre-close reconciliation.

How It Works in Practice

During an acquisition, three forces usually increase access risk. First, identity inventories are incomplete, so the acquiring team cannot reliably tell which service accounts exist, who owns them, or what they touch. Second, exception handling becomes normal: temporary AD trusts, cross-tenant app permissions, elevated API keys, and shared admin credentials are granted to keep migrations moving. Third, control ownership fragments across IT, security, application, and deal teams, which slows revocation when the integration plan changes.

Practitioners should handle this as a structured privilege-consolidation exercise, not a one-time access review. The practical sequence is to discover, classify, constrain, and revoke:

• Discover all human and non-human identities across both organisations, including dormant and shadow service accounts.
• Classify each account by business owner, system dependency, privilege level, and whether it can be replaced with JIT access.
• Constrain access with least privilege, short-lived secrets, and explicit expiry dates for every transitional exception.
• Revoke or rotate credentials as soon as a dependency is moved, retired, or re-authenticated in the target environment.

This is where NHI-specific evidence matters. NHI Management Group notes that 91.6% of secrets remain valid five days after notification in the Ultimate Guide to NHIs — Key Challenges and Risks, which shows how easily “temporary” access survives operational handoffs. For implementation discipline, align identity discovery and asset control with the NIST Cybersecurity Framework 2.0 and use the OWASP Non-Human Identity Top 10 to prioritise exposed credentials, excessive privilege, and weak lifecycle management.

These controls tend to break down when the acquired environment relies on undocumented automations, embedded secrets in code, or shared administrator accounts that are still needed to keep legacy systems alive.

Common Variations and Edge Cases

Tighter identity control often increases integration effort, requiring organisations to balance transaction speed against the risk of breaking production workflows. That tradeoff is real in regulated environments, during carve-outs, and in deals where legacy platforms cannot support modern federation or vaulting immediately.

There is no universal standard for every M&A scenario, but current guidance suggests treating the most sensitive identities differently from ordinary user accounts. Shared service accounts should be converted to individually owned workloads where possible. Privileged users from the acquired firm should be moved to time-bound elevation with explicit approval and logging rather than retained with standing access. For critical automations that cannot be redesigned quickly, restrict access to narrow system scopes and shorten credential TTL aggressively.

Edge cases often appear when external vendors, third-party support teams, or cross-company DevOps pipelines depend on the same credentials. The Ultimate Guide to NHIs highlights how broad third-party exposure and misconfigured vaults expand the blast radius, while the 52 NHI Breaches Analysis is useful for understanding how hidden service access frequently becomes the initial foothold. In practice, the hardest cases are not the obvious admin accounts but the “temporary” bridge credentials that survive long enough to become permanent.

Related resources from NHI Mgmt Group

• Why do mergers and acquisitions increase privileged access risk so quickly?
• How should security teams govern access requests for both users and service accounts?
• When do service accounts become a higher risk than ordinary user accounts?
• Why do service accounts and secrets with standing access increase risk in cloud environments?