Firewall Policy Checker Calculator

Example data table

Formula used

The checker assigns a Risk Score from 0 to 100 using a weighted model:

• ScopeFactor increases when source, destination, or protocol is any.
• ServiceWeight increases for broad ranges and high-risk ports (e.g., SSH, RDP, SMB, databases).
• LogAdjustment slightly reduces score when logging is enabled.
• HitAdjustment increases score for unused allow rules (hits = 0).
• Penalties add extra weight for shadowed, redundant, duplicate, and missing default deny patterns.

How to use this calculator

1. Enter each firewall rule with source, destination, protocol, service, and action.
2. Use CIDR notation for networks; use any for broad matches.
3. Optionally add hit counts from your reporting period to detect unused rules.
4. Click Submit to view findings above the form.
5. Use Download CSV or Download PDF to share results.
6. Refine rules and re-run to reduce risk score over time.

Policy coverage and match precision

Effective review starts by modeling what each rule can match. Sources and destinations expressed as precise CIDRs reduce accidental reach. A single “any” often expands exposure across zones, tenants, and VPN ranges. This checker highlights broad tokens and compares network masks to confirm whether a rule truly targets a host, a subnet, or an entire address space.

Shadowing and ordering signals

When a broader rule appears earlier, later intent can be silently bypassed. Shadowing is detected when an earlier rule contains the later rule’s source, destination, protocol, and service scope. In practice, this creates confusing tickets, inconsistent troubleshooting, and hidden allow paths. Reordering narrow exceptions above broad entries restores deterministic behavior and supports least‑privilege enforcement.

Redundancy reduction and rulebase health

Redundant entries inflate review effort and increase change risk. If an earlier rule already covers a later rule with the same action, the later entry adds no security value. Consolidation reduces policy length, accelerates audits, and improves analyst confidence during incidents. The tool flags redundant and duplicate signatures so owners can merge documentation and retire stale exceptions.

Risk scoring from scope and service exposure

The score combines scope factors with service sensitivity. Wide endpoint scope, protocol “any,” and large port ranges raise the baseline. High‑impact services such as SSH, RDP, SMB, and common database ports carry heavier weights because compromise can lead to rapid lateral movement. Logging slightly lowers risk because visibility improves response and validation during change windows.

Logging and hit counts for governance

Governance improves when denies are logged and unused rules are retired. Deny‑without‑logging obscures recon attempts and breaks baselining. Optional hit counts help identify zero‑use allows that quietly expand attack surface. A practical workflow is to mark zero‑hit rules for owner confirmation, set expiration dates, and remove them after a defined observation period.

Exportable reporting for reviews and change control

Structured exports turn findings into actionable change records. CSV outputs support filtering by severity and rule index, while PDF summaries help security reviews and CAB meetings for technical stakeholders as well. Pair exports with environment labels and review windows to keep context consistent across iterations. Re-run the checker after each revision to validate that risk score and issue counts trend downward.

FAQs

What rule format should I enter?

Use CIDR for source and destination, or write “any”. Set protocol as tcp, udp, icmp, or any. Services accept ports, ranges like 80-90/tcp, or names such as ssh, rdp, dns.

How does the checker detect shadowing?

A rule is shadowed when an earlier rule matches a superset of its source, destination, protocol, and service scope with a different action. The later rule will never take effect in ordered processing.

What counts as redundancy or duplication?

Redundancy occurs when an earlier rule fully covers a later rule with the same action. Duplication is an exact match signature repeated. Both increase review workload without adding protection.

How is the risk score calculated?

The score is a heuristic that increases with broad scope, protocol any, wide port ranges, and high-impact services. It also adds penalties for missing default deny, duplicates, shadowing, and unused allow rules.

Why are zero-hit rules flagged?

Zero-hit rules can be dead entries or forgotten exceptions. Removing them reduces attack surface and simplifies audits. Confirm with owners, define an observation window, then retire rules that remain unused.

Can I share results with auditors or change boards?

Yes. Use CSV for sorting and ticket creation, and PDF for review packs. Include the environment and review window notes so stakeholders can trace decisions across policy revisions.