Wildcard Access

Wildcard Access in Permissions and Policy Design

Wildcard access is usually introduced to reduce rule count and simplify administration, but the trade-off is that one pattern can cover far more resources than intended. That makes the design choice less about convenience and more about how precisely the access rule can be bounded, reviewed, and later understood by operators.

In practice, wildcard rules often appear in access control lists, cloud policy documents, certificate subjects, DNS names, and file-matching logic. The security question is whether the pattern is narrow enough to express the business need without accidentally matching resources, identities, or names that were never meant to be included.

How Wildcard Matching Changes the Security Boundary

A wildcard turns an exact match into a pattern match, which means the policy boundary is no longer one object or one principal, but a class of objects. That is powerful when the naming scheme is disciplined, yet risky when names are inconsistent, duplicated across environments, or created by different teams with different assumptions.

Because a wildcard can expand its reach silently as new resources are added, the real security boundary shifts from the policy line itself to the stability of the naming convention behind it. If the naming scheme changes, the access rule may start covering more than the reviewer expected.

Where Wildcards Commonly Go Wrong

The most common failure mode is overbroad matching. A wildcard that was meant to capture a controlled subset can also match temporary assets, test systems, shadow resources, or names with similar prefixes, creating unintended exposure.

Another failure mode is ambiguity. If humans cannot easily tell which resources match a pattern, the rule becomes hard to audit, hard to recertify, and easy to inherit into later designs without anyone realising how wide it is.

In access policy, that ambiguity often translates into privilege creep. In certificate and DNS contexts, it can broaden trust relationships in ways that are technically valid but operationally fragile.

When Wildcard Access Is Appropriate

Wildcard access is most defensible when the matching space is tightly governed, the naming convention is stable, and the operational benefit is clear. It is commonly used for controlled groups of resources, standardised environment naming, or repeatable patterns where enumerating every object would be brittle or expensive.

The safer use case is one where the wildcard expresses an intentional hierarchy, not a shortcut around incomplete inventory or poor policy design. When the pattern itself is doing the security work, the organisation needs strong ownership of the namespace that the pattern depends on.

Risk and Threat Considerations

Wildcard rules can create broad, hard-to-see trust paths that attackers or careless administrators may exploit if naming conventions or policy scopes are weak. The risk is highest where patterns touch high-value resources, shared certificates, or privilege-bearing access rules that are later reused across environments.

Failure mechanism: A pattern match expands beyond the intended set of resources, identities, or names because the namespace is too broad, the rule is too generic, or a later change introduces a matching object that was never reviewed.

Impact: Unintended access, excessive trust, certificate misuse, or policy sprawl can follow, especially when the wildcard is applied to production systems or privileged workflows.

Practitioner Guidance

Governance implication: Treat wildcard access as a policy design decision, not a convenience feature. Every wildcard should have a named owner, a documented intent, and a clear statement of what it is allowed to match.

What to watch for: Review any wildcard that spans multiple environments, high-value assets, or identities that can be created dynamically. If a rule cannot be explained quickly and unambiguously to another operator, it is usually too broad to leave unchallenged.

Practitioner takeaway: The safer wildcard is the one whose matching behaviour is obvious before it is deployed and still obvious months later when the namespace has changed.

Related resources from NHI Mgmt Group

• Why does a wildcard Access-Control-Allow-Origin setting increase risk for an API?
• What is the difference between a wildcard relation and granting access to every user individually?
• How should teams handle wildcard authorization so that API responses stay predictable during access checks?
• Wildcard Read Access