Should organisations challenge suspicious shared access or block it outright?

Why challenge first is usually the safer default

shared access is not automatically malicious, but it is often ambiguous enough that a hard block can punish legitimate behaviour and push users toward workarounds. Challenge-first keeps the control proportional: you verify intent, step up assurance, and preserve continuity when the access path is valid. That is especially useful when the same session, device, or workflow can be used by more than one authorised person.

A challenge is strongest when the suspicious signal is behavioural, not conclusive, for example an unfamiliar device, unusual geolocation, or a sudden change in usage pattern. In those cases, the control is doing two jobs at once: confirming the actor and testing whether the access is still within policy. If the access is legitimate, the user keeps moving; if not, the session becomes much easier to contain.

Microsoft SAS token exposure 2023 is a useful reminder that over-permissive shared access paths can quietly persist for a long time, so the goal is not to trust the first successful login forever. Pair challenge logic with a review of who can use the access, how long it lasts, and whether it should be rotated or narrowed before the next use.

When blocking becomes the right response

Blocking is the better option when the access is no longer just unusual but clearly out of scope, repeated, or abusive. If the same shared credential, token, or session is being used across unexpected contexts, the question is no longer “can we verify this user?” but “should this access path still exist at all?” At that point, challenge alone can become a delay tactic rather than a control.

Organisations should also block when the behaviour indicates policy violation, known compromise, or reuse that cannot be justified by the business process. The practical line is whether the access can still be safely defended as a controlled exception. If it cannot, continued challenge creates false confidence while leaving the underlying exposure intact.

That is why policies for shared access should define explicit tripwires for automatic denial, such as repeated failed step-up attempts, access from impossible locations, or use after revocation windows. Without those tripwires, teams tend to overuse challenge in situations that already warrant containment.

How to decide between challenge and block in practice

The decision should track the confidence you have in the access being legitimate and the blast radius if it is not. Challenge first when the signal is uncertain and the business cost of interruption is high. Block first when the signal is strong, the asset is sensitive, or the access path is a known source of abuse. The more the access resembles an entitlement rather than a user convenience, the less tolerant you should be of ambiguity.

Challenge also works best when it is paired with monitoring and a post-event review. If the same shared path keeps triggering step-up, that is evidence of a weak operating model, not a user problem. In that case, the control decision should move from real-time verification toward redesigning the access model so the shared path is no longer necessary.

For organisations that operate under stricter control regimes, the broader expectation is to restrict access by business need and minimise standing exposure. Standards such as PCI DSS v4.0, EU NIS2 Directive, and ISO/IEC 27001:2022 Information Security Management all reinforce the idea that access should be bounded, reviewable, and removed when it is no longer justified.

Practitioner Guidance

What to prioritise: Classify the access path before you classify the event. If the shared access is a routine operational pattern, challenge is usually the right first move; if it is an exception that has outlived its purpose, treat the exception itself as the problem.

What to verify: Confirm whether the access can be tied to an approved workflow, an expected user group, and a valid reason for shared use. If any of those are missing, the decision should move quickly toward blocking or narrowing the access rather than simply re-challenging it.

Common mistake: Teams often use challenge as a comfort blanket and stop there. That is acceptable only when the access remains clearly legitimate after verification; otherwise, repeated challenge without redesign just preserves a risky pattern.

Decision rule: If the access is suspicious but plausibly authorised, challenge first. If the access is repeatedly suspicious, outside policy, or tied to a sensitive system, block first and investigate the access model itself.

Practitioner takeaway: The best control choice is the one that reduces uncertainty without normalising weak shared access. Challenge is a verification step, not a substitute for fixing an access path that no longer deserves to exist.

Related resources from NHI Mgmt Group

• How should security teams run access reviews for non-human identities?
• How should security teams govern non-human identities that have persistent access?
• When do NHI access reviews create more value than a one-time cleanup?
• What is the difference between reviewing human access and reviewing NHIs?