What Is Any-Any Rule? Definition & Examples

An Any-Any Rule is a firewall rule that allows any source to reach any destination over any service or port, subject to the rule direction and scope. It creates broad exposure and is often left in place by mistake. Defenders should justify, time-limit, and replace it with narrowly defined access.

What an Any-Any Rule changes in firewall policy

An Any-Any Rule removes most of the filtering value of a firewall by allowing broad source, destination and service reachability. In practice, it turns the rule base into an exposure control problem, because the question is no longer whether traffic is allowed, but why such a wide path exists at all.

Why Any-Any Rules are dangerous

The main danger is that broad permission quietly defeats segmentation, least privilege and intended trust boundaries. A single permissive rule can expose internal systems to unnecessary east-west traffic, allow inbound paths that were never meant to be reachable, and make later incident containment much harder.

Any-Any Rules are especially risky because they are often created as temporary exceptions and then forgotten. That makes them a form of policy drift: the organisation believes a control exists, but the rule base still permits far more access than the design intended.

How defenders identify exposure

Exposure review starts with a complete firewall inventory and a current view of the rule base, including inherited, shadowed and unused rules. The important question is not only whether an Any-Any Rule exists, but whether it is active in a network path that reaches production assets, administrative services, partner links or internet-facing systems.

Good review practice compares the rule against business justification, expiry dates, ticket references and observed traffic. The Firewall Management Guide covers rule design, default deny policy, periodic review and rule cleanup in a way that fits this exact problem.

External validation should also use vendor advisories, change records and packet-flow evidence, because a rule that looks harmless on paper may still open a high-value path in the live environment. This is why firewall review is as much about operational context as it is about syntax.

How to reduce the blast radius

The practical fix is to replace Any-Any access with narrowly scoped rules that name the source, destination, protocol and port required for the business case. Where immediate removal is not possible, defenders should time-limit the exception, monitor its use closely and compensate with stronger inspection, segmentation and logging.

That approach aligns with broader hardening practice, including default-deny design, change control and rule recertification. A rule should survive only if someone can explain what it protects, why broader access is unnecessary and when the exception will end.

Risk and Threat Considerations

Any-Any Rules create a large attack surface because they can expose internal services, administrative interfaces and lateral movement paths that would otherwise be blocked. They also make misconfiguration more damaging, since one permissive rule can silently override the intent of many narrower controls.

Failure mechanism: A permissive rule bypasses segmentation and allows an attacker or accidental workload to reach more systems than intended, which can accelerate discovery, exploitation and spread after the first foothold.

Impact: The likely result is broader compromise scope, weaker containment and a longer time to detect and recover, especially when the rule reaches sensitive services or trust zones.

Standards & Framework Alignment

This section maps relevant standards and security frameworks to the operational risks and controls described in this guidance.

NIST SP 800-53 Rev 5, CIS Controls v8 and NIST CSF 2.0 set the governance and control requirements practitioners need to meet.

Framework	Control / Reference	Relevance
NIST SP 800-53 Rev 5	AC-4 — Information Flow Enforcement	Any-Any Rules directly weaken enforced traffic restrictions.
	CM-6 — Configuration Settings	Firewall rules are configuration settings that need controlled baselines.
	AU-6 — Audit Record Review, Analysis, and Reporting	Broad firewall rules require monitoring and review to spot misuse.
Recommendation — Enforce least-privilege network flows and remove overly broad allow rules. Baseline firewall rule standards and review deviations through change control. Review firewall logs for use of broad rules and investigate unexpected access patterns.
CIS Controls v8	CIS-4 — Secure Configuration of Enterprise Assets and Software	Firewall rule hygiene is part of secure configuration and exception management.
Recommendation — Harden firewall configurations and eliminate unnecessary allow-any exposures.
NIST CSF 2.0	PR.AA-05 — Least Privilege	Any-Any Rules directly conflict with least-privilege access design.
Recommendation — Reduce firewall permissions to the minimum paths required for business function.

Practitioner Guidance

Why practitioners should care: An Any-Any Rule is not just a bad configuration, it is a standing exception to the organisation’s access model. Treat it as a governed deviation that needs ownership, justification and an expiry condition, not as a normal firewall pattern.

What to watch for: Unexplained broad rules, old emergency changes, duplicate rules added during troubleshooting and any rule that remains after the original business need has passed. The strongest signal of risk is a rule that no one can clearly explain in current operational terms.

Practitioner takeaway: If a broad rule is temporarily unavoidable, make the exception explicit, measurable and short-lived, then replace it with the smallest access path that still supports the workload.

Any-Any Rule