IAM deny policies in GCP - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is an IAM deny policy in Google Cloud?

An IAM deny policy explicitly blocks certain actions or permissions, even if other policies allow them. It acts like a stop sign to prevent access.

beginner

How does an IAM deny policy differ from an allow policy?

Allow policies grant permissions to users or groups. Deny policies block permissions, overriding any allow policies that might grant access.

intermediate

Can an IAM deny policy be overridden by an allow policy?

No. Deny policies take precedence and cannot be overridden by allow policies. They always block the specified permissions.

intermediate

Why would you use an IAM deny policy in your cloud environment?

To add an extra layer of security by explicitly blocking risky or unwanted actions, even if other policies allow them. It helps prevent accidental or malicious access.

beginner

What happens if a user has both an allow and a deny policy for the same permission?

The deny policy wins. The user will be blocked from performing that action despite the allow policy.

What does an IAM deny policy do in Google Cloud?

A Creates new user accounts

B Grants permissions to users

C Logs user activities

D Blocks specified permissions even if allowed elsewhere

An IAM deny policy explicitly blocks permissions, overriding any allow policies.

If a user has an allow and a deny policy for the same permission, what happens?

A Deny policy takes precedence

B Allow policy takes precedence

C Both policies are ignored

D User gets partial access

Deny policies always override allow policies to block access.

Why use an IAM deny policy?

A To speed up network traffic

B To explicitly block risky actions

C To create new projects

D To monitor billing

Deny policies add security by blocking unwanted permissions.

Which statement is true about IAM deny policies?

A They override allow policies

B They are optional and ignored by default

C They grant permissions

D They only apply to service accounts

Deny policies override allow policies and apply to all identities.

Can an IAM deny policy be used to block access to a specific resource?

A Only if the user is an admin

B No, deny policies apply globally only

C Yes, deny policies can target specific resources

D Only if the resource is a VM

Deny policies can be scoped to specific resources to block access precisely.

Explain how IAM deny policies work and why they are important in Google Cloud security.

Think about how a stop sign works in traffic.

Describe a scenario where using an IAM deny policy would be beneficial.

Imagine you want to stop someone from entering a room even if they have a key.

Practice

1. What is the main purpose of an IAM deny policy in Google Cloud?

easy

A. To monitor user activities without changing permissions

B. To grant additional permissions to users or groups

C. To explicitly block certain permissions even if other policies allow them

D. To automatically delete unused resources

Solution

1. Step 1: Understand IAM deny policy function and compare with other policy types

   An IAM deny policy explicitly blocks permissions, overriding any allow policies. Unlike allow policies that grant access, deny policies prevent actions even if allowed elsewhere.

2. Final Answer:

   To explicitly block certain permissions even if other policies allow them -> Option C

3. Quick Check:

   IAM deny policy blocks permissions [OK]

Hint: Deny policies block permissions regardless of other allows [OK]

Common Mistakes:

• Confusing deny policies with allow policies
• Thinking deny policies grant permissions
• Assuming deny policies only monitor actions

2. Which of the following is the correct way to specify a deny rule in an IAM policy JSON snippet?

easy

A. "denyRules": [{"deniedPermissions": ["storage.buckets.delete"]}]

B. "allowRules": [{"allowedPermissions": ["storage.buckets.delete"]}]

C. "denyRules": [{"allowedPermissions": ["storage.buckets.delete"]}]

D. "denyRules": [{"deniedPermissions": "storage.buckets.delete"}]

Solution

1. Step 1: Identify correct deny rule syntax and check each option

   Deny rules use "denyRules" with "deniedPermissions" as a list of strings. "denyRules": [{"deniedPermissions": ["storage.buckets.delete"]}] correctly uses a list for "deniedPermissions". "allowRules": [{"allowedPermissions": ["storage.buckets.delete"]}] uses allowRules, which is incorrect. "denyRules": [{"allowedPermissions": ["storage.buckets.delete"]}] mixes denyRules with allowedPermissions, which is invalid. "denyRules": [{"deniedPermissions": "storage.buckets.delete"}] uses a string instead of a list, which is invalid.

2. Final Answer:

   "denyRules": [{"deniedPermissions": ["storage.buckets.delete"]}] -> Option A

3. Quick Check:

   Deny rules need deniedPermissions as list [OK]

Hint: Deny permissions must be in a list under deniedPermissions [OK]

Common Mistakes:

• Using allowRules instead of denyRules
• Providing deniedPermissions as a string instead of list
• Mixing allowedPermissions inside denyRules

3. Given this deny policy snippet:

{"denyRules": [{"deniedPermissions": ["compute.instances.start"]}]}

What happens if a user has an allow policy for compute.instances.start but this deny policy is applied?

medium

A. The user can start instances because allow policies override deny policies

B. The deny policy has no effect unless combined with a condition

C. The user can start instances only during business hours

D. The user cannot start instances because deny policies block the permission

Solution

1. Step 1: Understand deny policy precedence and apply to the example

   Deny policies always override allow policies for the specified permissions. Even if the user has an allow for starting instances, the deny rule blocks it.

2. Final Answer:

   The user cannot start instances because deny policies block the permission -> Option D

3. Quick Check:

   Deny overrides allow for blocked permissions [OK]

Hint: Deny always beats allow for the same permission [OK]

Common Mistakes:

• Thinking allow policies override deny policies
• Assuming deny policies need conditions to work
• Believing deny policies only log actions

4. You wrote this deny policy JSON but it does not block the intended permission:

{"denyRules": [{"deniedPermissions": "storage.objects.delete"}]}

What is the error?

medium

A. denyRules should be named allowRules

B. deniedPermissions should be a list, not a string

C. storage.objects.delete is not a valid permission

D. The policy must include a condition to work

Solution

1. Step 1: Check deniedPermissions data type and identify the error in the JSON

   deniedPermissions must be a list of strings, not a single string. The policy uses a string instead of a list, so it is invalid and won't block the permission.

2. Final Answer:

   deniedPermissions should be a list, not a string -> Option B

3. Quick Check:

   deniedPermissions requires a list [OK]

Hint: Use brackets [] for deniedPermissions list [OK]

Common Mistakes:

• Using string instead of list for deniedPermissions
• Confusing denyRules with allowRules
• Thinking conditions are mandatory

5. You want to deny the permission storage.buckets.delete only for requests made after 2024-01-01T00:00:00Z. Which IAM deny policy condition should you use?

hard

A. Use a condition with request.time > '2024-01-01T00:00:00Z'

B. Use a condition with resource.name == 'storage.buckets.delete'

C. No condition is needed; deny applies to all users

D. Use a condition with request.ip != 'company-network-ip-range'

Solution

1. Step 1: Identify the condition to restrict by time and match condition syntax

   To deny only for requests after the date, use a condition checking request.time > '2024-01-01T00:00:00Z'. Use a condition with request.time > '2024-01-01T00:00:00Z' uses request.time with inequality to apply after the date, which is correct.

2. Final Answer:

   Use a condition with request.time > '2024-01-01T00:00:00Z' -> Option A

3. Quick Check:

   Condition on request.time restricts deny by time [OK]

Hint: Use request.time condition to limit deny by time [OK]

Common Mistakes:

• Using resource.name instead of request.time for time check
• Using IP condition unrelated to time
• Applying deny without condition blocks all users