IAM Policy Deny Overriding Allow for Specific CIDR
This ANS-C01 practice question tests your understanding of network security, compliance and governance. Match the stated requirement to the specific cloud service, access model, or configuration option — many options are valid in isolation but not for this scenario. 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.
A security team has attached the above IAM policy to a user. The user tries to add an inbound rule to a security group that allows traffic from 0.0.0.0/0. The request is denied. However, the user is able to add a rule allowing traffic from 203.0.113.10. Which statement explains this behavior?
The Deny statement incorrectly uses the condition ec2:AuthorizeSecurityGroupIngress, which is not a valid condition key, so the Deny is ignored.
Why wrong: The condition key is valid; it uses the action name as a string condition key for the CIDR parameter.
B
The Deny statement denies all ec2:AuthorizeSecurityGroupIngress actions, so the user cannot add any inbound rules.
Why wrong: The Deny only denies when the CIDR is 0.0.0.0/0, not all ingress.
C
The Allow statement allows all ec2:AuthorizeSecurityGroupIngress actions from IPs in 203.0.113.0/24, so the user can add any rule.
Why wrong: The Deny overrides the Allow for the specific case of 0.0.0.0/0.
D
The Deny statement only denies the action when the CIDR is 0.0.0.0/0, which overrides the Allow for that specific case. For other CIDRs, the Allow applies because the user's source IP is within the allowed range.
The Deny is conditional on the CIDR being 0.0.0.0/0; other CIDRs are not denied, so the Allow statement permits the action.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The Deny statement only denies the action when the CIDR is 0.0.0.0/0, which overrides the Allow for that specific case. For other CIDRs, the Allow applies because the user's source IP is within the allowed range.
Option D is correct. The Deny statement denies the ec2:AuthorizeSecurityGroupIngress action only when the condition is satisfied—specifically, when the CIDR being added is 0.0.0.0/0. The Allow statement permits the action when the user's source IP falls within 203.0.113.0/24. Since the user's IP is 203.0.113.10, the Allow applies. However, the Deny overrides the Allow for the specific case of 0.0.0.0/0. For other CIDRs, such as 203.0.113.10, the Deny condition is not met, so the Allow takes effect. Option A is incorrect because the condition key is valid; Option B is incorrect because the Deny does not block all ingress actions; Option C is incorrect because the Allow is not unconditional—it depends on the user's source IP.
Key principle: Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
✗
The Deny statement incorrectly uses the condition ec2:AuthorizeSecurityGroupIngress, which is not a valid condition key, so the Deny is ignored.
Why it's wrong here
The condition key is valid; it uses the action name as a string condition key for the CIDR parameter.
✗
The Deny statement denies all ec2:AuthorizeSecurityGroupIngress actions, so the user cannot add any inbound rules.
Why it's wrong here
The Deny only denies when the CIDR is 0.0.0.0/0, not all ingress.
✗
The Allow statement allows all ec2:AuthorizeSecurityGroupIngress actions from IPs in 203.0.113.0/24, so the user can add any rule.
Why it's wrong here
The Deny overrides the Allow for the specific case of 0.0.0.0/0.
✓
The Deny statement only denies the action when the CIDR is 0.0.0.0/0, which overrides the Allow for that specific case. For other CIDRs, the Allow applies because the user's source IP is within the allowed range.
Why this is correct
The Deny is conditional on the CIDR being 0.0.0.0/0; other CIDRs are not denied, so the Allow statement permits the action.
Common exam trap: usable hosts are not the same as total addresses
Subnetting questions often tempt you into counting all addresses. In normal IPv4 subnets, the network and broadcast addresses are not usable host addresses.
Detailed technical explanation
How to think about this question
Subnetting questions test whether you can identify the network, broadcast address, usable range, mask and correct subnet. Slow down enough to calculate the block size correctly.
KKey Concepts to Remember
CIDR notation defines the prefix length.
Block size helps identify subnet boundaries.
Network and broadcast addresses are not usable hosts in normal IPv4 subnets.
The required host count determines the smallest suitable subnet.
TExam Day Tips
→Write the block size before choosing the subnet.
→Check whether the question asks for hosts, subnets or a specific address range.
→Do not confuse /24, /25, /26 and /27 host counts.
Key takeaway
Count usable hosts — not total addresses — and remember that the network and broadcast addresses are not available to hosts in standard IPv4 subnets.
Real-world example
How this comes up in practice
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.
Visual reference
What to study next
Got this wrong? Here's your next step.
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related ANS-C01 subnetting questions on CIDR, address ranges, and subnet selection.
Network Security, Compliance and Governance — This question tests Network Security, Compliance and Governance — CIDR notation defines the prefix length..
What is the correct answer to this question?
The correct answer is: The Deny statement only denies the action when the CIDR is 0.0.0.0/0, which overrides the Allow for that specific case. For other CIDRs, the Allow applies because the user's source IP is within the allowed range. — Option D is correct. The Deny statement denies the ec2:AuthorizeSecurityGroupIngress action only when the condition is satisfied—specifically, when the CIDR being added is 0.0.0.0/0. The Allow statement permits the action when the user's source IP falls within 203.0.113.0/24. Since the user's IP is 203.0.113.10, the Allow applies. However, the Deny overrides the Allow for the specific case of 0.0.0.0/0. For other CIDRs, such as 203.0.113.10, the Deny condition is not met, so the Allow takes effect. Option A is incorrect because the condition key is valid; Option B is incorrect because the Deny does not block all ingress actions; Option C is incorrect because the Allow is not unconditional—it depends on the user's source IP.
What should I do if I get this ANS-C01 question wrong?
Review block sizes, usable host formulas (2^n − 2), and how to find network and broadcast addresses for /24 through /30. Then practise related ANS-C01 subnetting questions on CIDR, address ranges, and subnet selection.
What is the key concept behind this question?
CIDR notation defines the prefix length.
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These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. A security engineer attaches the above IAM policy to an IAM user. The user then attempts to launch an EC2 instance from an IP address outside the 10.0.0.0/8 range. What will happen?
hard
A.The request will be allowed because the policy allows ec2:* on all resources.
✓ B.The request will be denied because the condition is not satisfied.
C.The request will be denied because the policy does not include a Deny statement.
D.The request will be allowed because the condition evaluates to true.
Why B: The policy allows ec2:* only when the source IP is within 10.0.0.0/8. If the user is coming from outside that range, the condition is not met, so the action is not allowed. The default is implicit deny, so the request will be denied. Option B is correct. Option A is wrong because the condition is not met. Option C is wrong because the policy does not deny explicitly; it just doesn't allow. Option D is wrong because the condition evaluates to false.
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