AWS_SSO_ASSIGN_PERMISSION_SET

Summary

Forestall ACL Alias	AWS_SSO_ASSIGN_PERMISSION_SET
Affected Object Types	AWSIAMUser|AWSIAMRole → AWSAccount
Exploitation Certainty	High
AWS IAM Action	sso:CreateAccountAssignment

Description

Account gate: This edge is only emitted for IAM principals that reside in the Organizations management account or an IAM Identity Center delegated-administrator account (service principal sso.amazonaws.com). Principals in any other member account receive AccessDenied from all SSO Admin APIs regardless of their IAM permissions.

An attacker with sso:CreateAccountAssignment can assign an already-privileged Permission Set to a principal they control (an SSO user or group they own). The permission set is the means; the account it provisions into is the prize. Once the assignment lands, the controlled principal signs in through the SSO portal and reaches that account with the provisioned AWSReservedSSO_* role. The edge therefore points to the account the attacker can take over.

Edge semantics: (Attacker:AWSIAMUser|AWSIAMRole) -[AWS_SSO_ASSIGN_PERMISSION_SET]-> (Target:AWSAccount)

Resource-faithful gate: sso:CreateAccountAssignment is authorized against three resource types at once — the IdC instance, the permission set, and the account. The edge is emitted only when the attacker's policy covers all three (a wildcard covers all of them). A policy that names only some resources fails the real call with an implicit deny on the missing one, so no edge is drawn.

Precondition: the assigned Permission Set must grant real privileges (managed or inline policy); assigning an empty Permission Set has no practical impact.

Identification

# Check if the attacker can create account assignments.
# Pass all three resource types — the action is authorized only when all are allowed.
aws iam simulate-principal-policy \
  --policy-source-arn <attacker-arn> \
  --action-names sso:CreateAccountAssignment \
  --resource-arns <instance-arn> <permission-set-arn> arn:aws:sso:::account/<account-id>

# List existing account assignments to understand scope
aws sso-admin list-account-assignments \
  --instance-arn <instance-arn> \
  --account-id <account-id> \
  --permission-set-arn <permission-set-arn>

# List policies attached to the permission set
aws sso-admin list-managed-policies-in-permission-set \
  --instance-arn <instance-arn> \
  --permission-set-arn <permission-set-arn>

PowerShell (AWS Tools):

Get-SSOAdminAccountAssignmentList -InstanceArn "<instance-arn>" -AccountId "<account-id>" -PermissionSetArn "<permission-set-arn>"

Exploitation

# Assign the privileged Permission Set to the attacker-controlled SSO user
aws sso-admin create-account-assignment \
  --instance-arn <instance-arn> \
  --target-id <account-id> \
  --target-type AWS_ACCOUNT \
  --permission-set-arn <permission-set-arn> \
  --principal-type USER \
  --principal-id <attacker-sso-user-id>

Mitigation

• Restrict sso:CreateAccountAssignment to dedicated Identity Center administrator roles.

• Use SCPs to limit which accounts and which Permission Sets can receive new assignments.

• Regularly audit account assignments and alert on new assignments to privileged Permission Sets.

• Apply just-in-time access controls so assignments require approval workflows.

• Use permission boundaries on Permission Sets to limit blast radius even if an unauthorized assignment is created.

Detection

CloudTrail Event	Description	Key Fields
CreateAccountAssignment	A Permission Set was assigned to a principal in an account	requestParameters.permissionSetArn, requestParameters.principalId, requestParameters.principalType, requestParameters.targetId, userIdentity.arn

Alert on any CreateAccountAssignment event for Permission Sets with high-privilege policies. Pay extra attention when the assignee principal was recently created or is otherwise unexpected.

References

• AWS IAM Identity Center: Manage Account Assignments

• AWS SSO Admin API: CreateAccountAssignment

• HackTricks: AWS IAM Identity Center Privilege Escalation

• Rhino Security Labs: AWS Privilege Escalation Methods