Quick Answer
The most significant security concern is that SSH is allowed from any source, because permitting TCP port 22 from 0.0.0.0/0 exposes every VM in the VPC to brute-force attacks, unauthorized access, and potential compromise. This violates the principle of least privilege, as a VPC firewall rule should restrict SSH access to only specific, trusted source IP ranges rather than the entire internet. On the Google Professional Cloud Network Engineer exam, this scenario tests your ability to identify overly permissive ingress rules, a common trap where engineers mistakenly use 0.0.0.0/0 for administrative access without considering the security implications. A key memory tip is to think of “SSH from any” as “SSH from every attacker”—always pair administrative protocols with a specific source CIDR or use IAP (Identity-Aware Proxy) for secure tunneling instead.
This PCNE practice question tests your understanding of designing, planning, and prototyping a gcp network. This is a configuration task: choose the command set that satisfies every stated requirement. Small differences — like 'secret' vs 'password' or 'transport input ssh' vs 'all' — change whether the answer is correct. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
Refer to the exhibit. A network engineer reviews the firewall rules in a VPC. What is the most significant security concern?
There is no deny rule.
Why wrong: Default deny is implicit; having no explicit deny is normal.
RDP is allowed from 10.0.0.0/8.
Why wrong: This is a private range and acceptable for internal access.
SSH is allowed from any source.
0.0.0.0/0 includes all public IPs, which is insecure.
Firewall rules are not in order.
Why wrong: No conflicting rules; order is not a concern here.
Answer choices
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
SSH is allowed from any source.
Option C is correct because allowing SSH (TCP/22) from any source (0.0.0.0/0) exposes the VPC instances to brute-force attacks, unauthorized access, and potential compromise. This violates the principle of least privilege and is a critical security misconfiguration in a VPC firewall rule.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
There is no deny rule.
Why it's wrong here
Default deny is implicit; having no explicit deny is normal.
RDP is allowed from 10.0.0.0/8.
Why it's wrong here
This is a private range and acceptable for internal access.
SSH is allowed from any source.
Why this is correct
0.0.0.0/0 includes all public IPs, which is insecure.
Related concept
Read the scenario before looking for a memorised answer.
Firewall rules are not in order.
Why it's wrong here
No conflicting rules; order is not a concern here.
Common exam traps
Google Cloud often tests the misconception that a missing explicit deny rule is a security risk, but in GCP VPC, the implicit deny at the end of the rule evaluation makes an explicit deny unnecessary unless you need to override a higher-priority allow rule.
Detailed technical explanation
In GCP VPC, firewall rules are stateful and evaluated by priority (0–65535), with lower numbers taking precedence. Allowing SSH from 0.0.0.0/0 means any IP on the internet can attempt to connect, making the instance a target for automated scanning and credential stuffing. A best practice is to restrict SSH to specific source ranges (e.g., a bastion host or corporate VPN CIDR) and use IAP TCP forwarding for zero-trust access.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
A company's IT admin needs to give a contractor read-only access to production logs without sharing account credentials. Using role-based access control (RBAC) and temporary scoped permissions — not a permanent shared password — is the correct pattern. Questions like this test whether you can apply least-privilege access across cloud identity services.
What to study next
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FAQ
Designing, planning, and prototyping a GCP network — This question tests Designing, planning, and prototyping a GCP network — Read the scenario before looking for a memorised answer..
The correct answer is: SSH is allowed from any source. — Option C is correct because allowing SSH (TCP/22) from any source (0.0.0.0/0) exposes the VPC instances to brute-force attacks, unauthorized access, and potential compromise. This violates the principle of least privilege and is a critical security misconfiguration in a VPC firewall rule.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 30, 2026
This PCNE practice question is part of Courseiva's free Google Cloud certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the PCNE exam.
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