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Introduction:
AWS Identity and Access Management (IAM) relies on an eventual consistency model that can leave a window of up to four seconds between policy attachment and enforcement—a gap that attackers with admin access can exploit to remove a deny-all policy before it takes effect. This critical oversight has been a hidden risk for years, but a newly documented technique using Service Control Policies (SCPs) at the AWS Organizations level now makes quarantine policies irremovable, regardless of the attacker’s privilege within the account. This article dissects the attack vector, provides a step‑by‑step guide to deploying SCP‑based containment, and explores its limitations and future implications.
Learning Objectives:
- Understand the IAM eventual consistency attack vector and how attackers bypass quarantine policies.
- Learn to configure AWS Organizations and craft SCPs for irremovable account containment.
- Implement and test a defense that locks down compromised AWS identities before they can react.
You Should Know
1. The IAM Eventual Consistency Attack Vector
When a deny-all policy is attached to a compromised IAM identity (user or role), AWS does not apply the policy instantly. There is a brief window—typically 2 to 4 seconds—during which the policy change is propagating across AWS’s distributed systems. An attacker with admin privileges can use this window to detach the policy before it becomes effective, effectively nullifying the quarantine.
Step‑by‑step demonstration:
- Prerequisite: AWS CLI installed and configured with credentials of a compromised admin user/role.
- Attacker’s view: The defender attaches a deny-all policy (e.g.,
AWSDenyAll) to the attacker’s role. - During the 4-second window: The attacker runs the following command (Linux/macOS/Windows with AWS CLI) to list and detach the policy:
List attached policies aws iam list-attached-role-policies --role-name AttackerRole Detach the deny-all policy aws iam detach-role-policy --role-name AttackerRole --policy-arn arn:aws:iam::aws:policy/AWSDenyAll
If executed quickly enough, the detach operation succeeds before the deny policy is fully enforced. The attacker then retains full access.
2. Prerequisites: Setting Up AWS Organizations
SCPs are a feature of AWS Organizations, so you must have an organization set up with the target account as a member. If you haven’t enabled Organizations, follow these steps:
1. Enable AWS Organizations in the management account:
- Via CLI: `aws organizations create-organization –feature-set ALL`
– Or via AWS Console: Navigate to AWS Organizations and click “Create organization”.
- Create an Organizational Unit (OU) for quarantine purposes:
aws organizations create-organizational-unit --parent-id r-xxxx --name QuarantineOU
- Move the compromised account into the Quarantine OU:
aws organizations move-account --account-id 123456789012 --source-parent-id r-yyyy --destination-parent-id ou-zzzz-xxxxxxxx
This step ensures the SCP you attach to the OU will apply to the account.
3. Crafting the SCP Quarantine Policy
SCPs are JSON policies that set maximum permissions for all IAM users and roles in an account (the root user is exempt). To create an irremovable quarantine, we need a policy that denies all actions except those absolutely required for management (if any). For a complete lockdown, use:
{
"Version": "2012-10-17",
"Statement": [
{
"Sid": "DenyAllAccess",
"Effect": "Deny",
"Action": "",
"Resource": ""
}
]
}
Save this as deny-all.json. Then create the SCP in AWS Organizations:
aws organizations create-policy --content file://deny-all.json --name QuarantineSCP --description "Deny all actions" --type SERVICE_CONTROL_POLICY
Note the returned `PolicyId` (e.g., `p-12345678`).
4. Attaching the SCP to the Compromised Account
Attach the SCP to the OU containing the compromised account. Because SCPs are managed by the organization’s management account, the attacker—even with admin rights inside the member account—cannot detach or modify the SCP.
aws organizations attach-policy --policy-id p-12345678 --target-id ou-zzzz-xxxxxxxx
If you need to attach directly to an account (not an OU), use the account ID as the target. The effect is immediate: the SCP is evaluated before any IAM policy, so all API calls from the member account are denied. The attacker’s session will start receiving `AccessDenied` errors within seconds.
5. Verification and Testing
To confirm the quarantine is active and irremovable, perform these tests from within the member account:
- Attempt any AWS CLI command (e.g.,
aws s3 ls). You should see:An error occurred (AccessDenied) when calling the ListBuckets operation: User is not authorized to perform: s3:ListAllMyBuckets because no identity-based policy allows the s3:ListAllMyBuckets action
- Try to detach the SCP from within the member account (it’s impossible because SCPs are not visible or manageable in the member account):
aws organizations detach-policy --policy-id p-12345678 --target-id 123456789012
This will fail with `AccessDeniedException` because the member account lacks Organizations permissions.
-
Attempt to leave the organization (also blocked by default unless explicitly allowed).
6. Limitations and Considerations
- Requires AWS Organizations: Single, standalone AWS accounts cannot use SCPs. For those, consider using IAM permissions boundaries or resource-based policies, though these can be removed by an admin if the attack window is exploited.
- Root user exemption: The AWS account root user is not restricted by SCPs. If the attacker has root credentials, this defense fails. Always protect root credentials with MFA and avoid using them.
- Policy evaluation delay: While SCPs are enforced nearly instantly, there may be a brief propagation delay (a few seconds). However, because the SCP is attached at the organization level and the attacker cannot modify it, this delay is irrelevant—the attacker’s only chance is to act during that window, but they cannot remove the SCP itself.
- Management account exposure: The organization’s management account holds the keys to SCPs. Compromise of that account would allow an attacker to detach the quarantine. Therefore, the management account must be locked down with the highest security standards.
7. Alternative Defenses for Standalone Accounts
If you cannot use AWS Organizations, you can still harden your environment:
– IAM Permissions Boundaries: Set a boundary that limits the maximum permissions a role can have. An attacker could remove the boundary during the eventual consistency window if they have `iam:PutRolePermissionsBoundary` or `iam:DeleteRolePermissionsBoundary` permissions. To mitigate, remove these permissions from all principals.
– Resource-based Policies: For specific services (S3 buckets, SQS queues, etc.), resource-based policies can deny access even if IAM allows it. However, these do not lock down the entire account.
– AWS CloudTrail + Lambda: Use CloudTrail to detect policy changes and trigger a Lambda function that re-attaches the deny policy. This is reactive and may still leave a small window, but it can reduce risk.
What Undercode Say
- Key Takeaway 1: The IAM eventual consistency window is a real, exploitable gap. Organizations relying solely on IAM policies for incident response must adopt SCPs or other preventive controls to make quarantine policies truly irremovable.
- Key Takeaway 2: SCPs provide a robust identity-level containment mechanism, but they require AWS Organizations and careful management of the root user and management account. The technique shifts the defense from the compromised account to a higher authority, breaking the attacker’s ability to countermand the quarantine.
The attack surface exposed by IAM’s eventual consistency is a classic example of how distributed systems trade immediate consistency for availability. While the window is tiny, automated tools can exploit it reliably. The SCP-based solution elegantly removes the attacker’s access to the policy management plane, but it also introduces new operational complexities. Security teams must balance the need for rapid containment with the architectural constraints of their AWS environment. As cloud providers evolve, we may see native “lockdown” features that close this gap without requiring organization-level constructs, but for now, SCPs are the gold standard.
Prediction:
In the next 12–18 months, AWS is likely to introduce a new IAM feature that allows “emergency deny” policies that take effect instantly or are immune to removal by the principal they target. This could be a form of “immutable policies” or a quarantine mode that can be triggered from a central security hub. Meanwhile, we will see a rise in automated attack tools that specifically target this 4‑second window, forcing defenders to adopt organization-level controls or third-party cloud security platforms that offer real-time policy enforcement. The disclosure of this technique will also prompt cloud providers to document eventual consistency behaviors more transparently and provide official mitigation guidance.
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IT/Security Reporter URL:
Reported By: Eduard K – Hackers Feeds
Extra Hub: Undercode MoN
Basic Verification: Pass ✅
