What causes any-any rules?

What creates any-any firewall rules?

Any-any rules usually come from operational shortcuts rather than design intent. They are created when teams need something to work fast, do not scope the source or destination tightly enough, or leave a broad temporary exception in place after the immediate problem is solved. The pattern is less a technical necessity than a control lapse.

In practice, these rules tend to show up where change control is weak, ownership is unclear, or the rule review process is too slow to keep up with business pressure. A rule that is meant to be temporary can become permanent simply because nobody is accountable for revisiting it. That is why rule lifecycle management matters as much as initial firewall design.

In well-run environments, any-any entries are treated as exceptions that must be explained, time-bounded and tied to a specific business need. The goal is not only to make the firewall stricter, but to make every broad rule visible enough that it can be challenged, narrowed or removed.

Why any-any rules survive longer than they should

These rules often persist because they reduce friction for operators under pressure. When an application breaks, a patch is urgent, or a vendor needs emergency access, the fastest path is sometimes to open the network broadly and come back later. If that follow-up never happens, the rule remains as technical debt with security impact.

Another common cause is poor scoping. Teams may know the traffic is “needed somewhere” but not enough to define exact ports, hosts, subnets or application paths. That uncertainty leads to permissive entries that are easier to approve in the moment but much harder to defend later.

Firewall Management Guide covers the rule review, cleanup and change control practices that prevent temporary broad access from becoming normalised.

How to spot the control failure behind the rule

Any-any rules are a symptom of weak governance around firewall policy, not just a bad line in a rulebase. If exceptions are approved without expiry dates, if ownership is not recorded, or if reviews happen only during audits, the environment will accumulate broad permits faster than it can remove them.

The same pattern can also reveal a deeper architecture issue. When teams rely on broad network access to make systems function, the real problem may be missing segmentation, unclear service dependencies or poorly documented application flows. In that case, the firewall is compensating for uncertainty elsewhere in the stack.

Good practice is to treat each broad rule as a signal to identify the exact dependency that forced it. Once the dependency is known, the rule can usually be reduced to a smaller trust boundary rather than left as a permanent open path.

Risk and Threat Considerations

Any-any rules create unnecessary exposure because they turn a firewall from a filtering control into a near-open pathway. If an attacker reaches one system on either side of the rule, broad reachability can make lateral movement, service discovery and data access much easier than intended.

Failure mechanism: The firewall accepts traffic without meaningful source, destination or service restriction, so the environment loses a key layer of segmentation and blast-radius control. Broad exceptions also tend to hide behind legitimate operational need, which makes them harder to question during routine reviews.

Impact: A single compromised host, stolen credential or exposed service can gain far more reach than it should. That increases the chance of privilege escalation, credential harvesting, service abuse and wider incident impact across internal networks.

Practitioner Guidance

What to prioritise: Start with the rules that expose production systems, internal management planes or sensitive data paths. Those entries create the highest blast radius and should be the first candidates for narrowing or removal.

What to verify: For every broad rule, confirm the business owner, the reason it exists, the systems it is meant to support and the expiry or review date. If any of those details are missing, treat the rule as uncontrolled rather than approved.

Practitioner takeaway: Broad firewall rules are usually a process failure expressed as a network rule, so the fix is to restore ownership, scope and expiry discipline, not to assume the exception is inherently justified.

Related resources from NHI Mgmt Group

• What is the difference between a rules-based secret scanner and a hybrid scanner?
• What is the difference between static access rules and evidence-based access decisions?
• When does context-aware DLP matter more than rules-based inspection?
• Why do token-based attacks often evade standard detection rules?