What are common mistakes with Any-Any Rule?

Why an Any-Any Rule Becomes a Standing Exposure

An Any-Any rule is rarely just a temporary testing shortcut once it lands in a live policy set. The common mistake is treating it as a neutral placeholder when it actually removes the filtering logic that makes the rulebase meaningful. That can expose multiple paths at once, so the real question is not whether it works, but what blast radius it creates if left unchanged.

Another common error is assuming the rule is low risk because traffic is logged. Logging is useful, but it does not prevent unauthorized movement, unnecessary reachability, or accidental dependency on a permissive rule. If the rule still allows broad source, destination, and service combinations, it remains a control gap even when every hit is recorded.

Teams also underestimate how quickly a temporary exception becomes normalised. Once an Any-Any rule supports a test, migration, or troubleshooting effort, it is easy for owners to forget the original purpose, lose the expiry condition, or fail to revisit whether the business need still exists. The longer it remains, the harder it becomes to separate intentional access from policy drift.

How to Scope or Replace It Without Breaking Work

The practical fix is to replace the broad rule with a narrower one that matches the actual communication path, then define why the exception exists and when it will be removed. For a firewall context, that means scoping by application, source network, destination network, port, protocol, and time window rather than leaving the policy open-ended. The Firewall Management Guide is a useful reference for rule design, cleanup, and periodic review.

Just as important, document the owner and review date for every exception. A rule that cannot be tied to a business justification, a change record, or an expiry date should be treated as unfinished work, not an acceptable control state. If the purpose is testing, use the shortest practical duration and remove the rule as soon as validation is complete.

Replacement should also preserve operational intent. If the rule exists because a team needs temporary reachability for rollout or troubleshooting, convert that need into a bounded exception rather than a permanent policy. That keeps the access path understandable and makes later review possible without reconstructing the original rationale from memory.

What Reviewers Miss in Broad Allow Rules

Broad allow rules are often missed because they sit inside larger policy sets that appear well managed. Reviewers may focus on obvious deny failures, while the Any-Any entry quietly bypasses the normal discipline of least privilege, segmentation, and change control. In practice, the risk is not only unauthorized access, but also the loss of confidence that the rulebase expresses current intent.

For teams managing multiple exception types, the pattern is consistent: the dangerous part is not the existence of an exception, but the failure to prove it is bounded, necessary, and actively owned. A rule that has no removal date, no purpose statement, or no named reviewer should be treated as a candidate for immediate closure. The same governance discipline that applies to firewall exceptions also applies to other temporary access shortcuts, such as Top 10 MFA Mistakes when exceptions are left in place after the original need has passed.

Risk and Threat Considerations

An Any-Any rule creates a standing exposure because it collapses filtering across sources, destinations, and services. That broad reach can be harmless during a controlled test, but if it remains in production it can provide an attacker or misconfigured workload with far more access than intended.

Failure mechanism: The rule bypasses the normal decision points that should restrict traffic by business purpose, asset scope, and time. Once that happens, lateral movement, data exposure, and unintended service reachability become much easier to achieve or to overlook during review.

Impact: The result is excessive connectivity, weaker containment, and a larger blast radius if another control fails. Logging may show the traffic, but it does not restore the protection the rule removed.

Practitioner Guidance

What to prioritise: Remove any Any-Any rule that no longer has a live, documented operational purpose. If it still has a valid use, narrow it to the smallest workable source, destination, service, and time scope.

What to verify: Confirm that every exception has an owner, a reason, and a removal date. If any of those are missing, treat the rule as an outstanding remediation item rather than a managed exception.

Common mistake: Teams leave the rule in place because they expect logging, monitoring, or general trust in the network to make it safe. That is the wrong test, because visibility does not equal control.

Practitioner takeaway: An Any-Any rule is acceptable only as a short-lived, explicitly owned exception, not as a standing policy artifact that quietly replaces segmentation and least privilege.

Related resources from NHI Mgmt Group

• What are common mistakes with a Shadowed Rule?
• What are common mistakes with Firewall Rule Review?
• What mistakes do crypto businesses make when preparing for Australia’s Travel Rule and AML reforms?
• What are the most common mistakes organisations make when launching green banking or telecom initiatives?