path: root/content/blog/2026-02-21-auditing-aws-iam.org

#+date: [2026-02-21 Sat 18:58:39]
#+title: Auditing AWS IAM Identity Center Assignments
#+description: How to audit IAM Identity Center access assignments in AWS using a shell script, including what to look for, common exceptions, and how to write up findings.
#+slug: auditing-aws-iam

If you've ever asked an IT team for a list of who has access to an AWS account,
you've probably received a spreadsheet that was already out of date. Or worse,
an out-of-context screenshot that doesn't explain anything. IAM Identity Center
doesn't make this easy to extract through the console, and most teams don't have
a repeatable process for pulling it. This post walks through a script that does
it for you and explains what to look for once you have the output.

The script is available at [[https://github.com/audit-labs/audit-tools/blob/main/applications/aws/aws_iam_users.sh][audit-labs/audit-tools]].

* Background: How AWS Provisions Access

Before running anything, it helps to understand the different ways AWS can be
architected to grant access. You may encounter any of these in practice,
sometimes within the same organization, and knowing how they differ tells you
where to look during an audit and which questions to ask.

** Traditional IAM Users

The original AWS access model. An IAM user is an identity created directly
inside a single AWS account. It has a username, optional console password, and
optional access keys for programmatic access. Permissions are granted by
attaching IAM policies directly to the user, or by adding the user to an IAM
group that has policies attached to it.

You'll still see IAM users in older environments, smaller organizations, and in
cases where a service or application needs long-lived programmatic credentials.
The core problem with IAM users at scale is that they're account-scoped, meaning
a user in ~Account A~ has no relationship to a user in ~Account B~, even if they're
the same person. Organizations with dozens or hundreds of accounts end up with a
fragmented identity landscape that's difficult to review and even harder to
deprovision consistently.

From an audit perspective, IAM users are high-risk when they have active access
keys (long-lived credentials that don't expire unless explicitly rotated or
revoked) or when policies are attached directly to the user rather than
inherited through a group.

** IAM Groups

IAM groups are a way to organize IAM users within a single account and attach
policies to multiple users at once. A user inherits all permissions from every
group they belong to. Groups themselves cannot assume roles or make API calls.
They exist only as a convenience for managing user permissions in bulk.

Groups help with consistency, but they don't solve the cross-account problem. An
IAM group in ~Account A~ still has no bearing on access in ~Account B~. You'll see
groups used alongside IAM users in the same environments where IAM users are
prevalent.

** IAM Roles

Roles are the most flexible identity construct in AWS. Unlike users, roles
aren't tied to a specific person. They're assumed temporarily by whoever (or
whatever) is authorized to use them. When an entity assumes a role, AWS issues
short-lived credentials that expire automatically, usually after an hour.

Roles are used in several contexts:

- *Cross-account access*: ~Account A~ can grant a role in ~Account B~ the ability to
  be assumed by principals in ~Account A~. This is how many organizations handle
  access across accounts without using IAM Identity Center.
- *Service roles*: AWS services like Lambda, EC2, and ECS use roles to make API
  calls on your behalf. An EC2 instance with an attached instance profile is
  assuming a role every time it calls an AWS API.
- *Federated access*: External identity providers (Active Directory, Okta, etc.)
  can be configured to exchange a user's external credentials for temporary AWS
  role credentials via SAML or OIDC. This is an older pattern that predates IAM
  Identity Center.
- *Break-glass access*: A role with broad permissions that is locked down by
  default and only assumed in emergencies. A common method for securing these
  accounts is vaulting the credentials in a PAM platform like CyberArk.

From an audit perspective, roles require you to look at the trust policy (who is
allowed to assume the role) as well as the permission policy (what the role can
do once assumed). Both matter. A role with ~AdministratorAccess~ is only as risky
as its trust policy is permissive.

** IAM Policies

Policies are the documents that define permissions. They're not an access
pattern on their own, but understanding the three types helps when reviewing
output from any access audit:

- *AWS managed policies* are created and maintained by AWS. Examples include
  ~AdministratorAccess~, ~ReadOnlyAccess~, and job-function policies like ~Billing~.
  They're convenient but broad: ~AdministratorAccess~ is a single policy that
  grants full access to every AWS service.
- *Customer managed policies* are created by the organization. They offer more
  precise control and can be reused across users, groups, and roles. Better
  practice than relying entirely on AWS managed policies for anything sensitive.
- *Inline policies* are embedded directly into a specific user, group, or role
  rather than existing as a standalone resource. They can't be reused and are
  easier to miss during reviews. When you see an inline policy in audit output,
  treat it as something that warrants a closer look — they're often added ad hoc
  to solve a specific problem and not always well documented.

** IAM Identity Center

IAM Identity Center (formerly AWS SSO) is the current recommended approach for
human access in multi-account AWS Organizations. It sits above individual
accounts and provides centralized access management across all of them from a
single place.

It connects to an identity source, such as AWS's own directory, Active
Directory, or an external IdP like Okta or Entra ID, and uses that as the source
of truth for users and groups. Access is configured within Identity Center
itself, not inside individual accounts.

The key construct is the permission set: a named bundle of IAM policies
(managed, customer managed, and/or inline) that defines what a principal can do.
When you assign a permission set to a user or group for a specific account, AWS
creates a temporary IAM role in that account that the user assumes when they
access it. The credentials are short-lived and scoped to the session.

The standard architecture: users belong to groups in the identity source, groups
are assigned permission sets for specific accounts in Identity Center, and users
inherit access through their group memberships. Provisioning and deprovisioning
happen at the group membership level, not by touching individual account
assignments.

Direct user assignments (where a user is assigned a permission set without going
through a group) are possible but generally a control gap, because they bypass
the group-based review and provisioning process.

If the organization uses Identity Center, the access population you need to
review lives there, not inside individual accounts. Looking at IAM users and
roles within an account will give you an incomplete picture. You'll see the
temporary roles that Identity Center creates, but not who is assigned to them or
why.

* What the Script Does

The script works against a single named AWS account and produces a JSON report
of every user and group assignment, along with the permission set and policies
attached to each assignment.

It runs in four steps:

1. Finds the IAM Identity Center instance and looks up the target account ID by
   name
2. Lists all permission sets provisioned to that account
3. For each permission set, retrieves all user and group assignments, resolves
   their names from the Identity Store, and fetches the managed and inline
   policies attached to the permission set
4. Writes everything to a JSON file named ~report_<account_name>.json~

The script caches permission set details and principal names to avoid redundant
API calls when the same permission set or user appears in multiple assignments.

* Prerequisites

You'll need:

- AWS CLI installed and configured with credentials that have read access to
  ~sso-admin~, ~identitystore~, and ~organizations~
- ~jq~ installed (used throughout the script for JSON parsing)
- The name of the AWS account you want to audit (must match exactly as it
  appears in AWS Organizations)

Set the account name at the top of the script before running:

#+begin_src bash
ACCOUNT_NAME="your-account-name"
#+end_src

Then make the script executable and run it:

#+begin_src bash
chmod +x aws_iam_users.sh
./aws_iam_users.sh
#+end_src

#+caption: Script Output
#+attr_html: :alt Terminal output of aws_iam_users.sh showing discovered assignments for the cmc account.
[[https://img.cleberg.net/blog/20260221-auditing-aws-iam/script.webp]]


* Key Snippet: Resolving Principal Names

The part of the script most worth understanding is how it resolves user and
group names. AWS stores principals in Identity Center by ID, not by name. To get
a readable name, the script calls the Identity Store API separately for each
principal:

#+begin_src bash
if [ "$PRINCIPAL_TYPE" == "USER" ]; then
    PRINCIPAL_NAME=$(aws identitystore describe-user \
        --identity-store-id "$IDENTITY_STORE_ID" \
        --user-id "$PRINCIPAL_ID" \
        --query "UserName" --output text 2>/dev/null)
elif [ "$PRINCIPAL_TYPE" == "GROUP" ]; then
    PRINCIPAL_NAME=$(aws identitystore describe-group \
        --identity-store-id "$IDENTITY_STORE_ID" \
        --group-id "$PRINCIPAL_ID" \
        --query "DisplayName" --output text 2>/dev/null)
fi
#+end_src

This is also where the cache matters. If the same user appears across multiple
permission set assignments (which is common), the script reuses the stored name
rather than making a redundant API call.

* Reading the Output

The script produces a JSON array where each element represents a single
principal-to-permission-set assignment. Here's an example:

#+begin_src json
[
  {
    "principal": {
      "type": "GROUP",
      "name": "testgroup1"
    },
    "permission_set": {
      "name": "AdministratorAccess",
      "policies": {
        "managed_policies": [
          "arn:aws:iam::aws:policy/AdministratorAccess"
        ],
        "inline_policy": "{\"Version\":\"2012-10-17\",\"Statement\":[{\"Sid\":\"Statement2\",\"Effect\":\"Deny\",\"Action\":[\"a4b:*\"],\"Resource\":[\"*\"]}]}"
      }
    }
  },
  {
    "principal": {
      "type": "USER",
      "name": "iamtestuser1"
    },
    "permission_set": {
      "name": "AdministratorAccess",
      "policies": {
        "managed_policies": [
          "arn:aws:iam::aws:policy/AdministratorAccess"
        ],
        "inline_policy": "{\"Version\":\"2012-10-17\",\"Statement\":[{\"Sid\":\"Statement2\",\"Effect\":\"Deny\",\"Action\":[\"a4b:*\"],\"Resource\":[\"*\"]}]}"
      }
    }
  },
  {
    "principal": {
      "type": "USER",
      "name": "iamtestuser1"
    },
    "permission_set": {
      "name": "Billing",
      "policies": {
        "managed_policies": [
          "arn:aws:iam::aws:policy/job-function/Billing"
        ],
        "inline_policy": ""
      }
    }
  }
]
#+end_src

#+caption: JSON Report
#+attr_html: :alt The contents of report_cmc.json showing principal and permission set assignments.
[[https://img.cleberg.net/blog/20260221-auditing-aws-iam/json.webp]]

A few things to look for when reviewing this output:

*Direct user assignments*: ~iamtestuser1~ is assigned ~AdministratorAccess~ directly
as a USER, not through a group. Access should generally be provisioned through
groups so that provisioning and deprovisioning are tied to group membership, not
managed case-by-case. A direct user assignment to a high-privilege permission
set warrants a conversation with IT about why it exists.

*AdministratorAccess*: This is AWS's broadest managed policy, which allows full
access to everything in the account. Note who has it and whether that's
appropriate. In many environments, even senior engineers shouldn't have standing
~AdministratorAccess~; it should be reserved for break-glass accounts or
infrastructure teams with a documented need.

*Inline policies*: The ~inline_policy~ field in this example contains a Deny
statement for ~a4b:*~ (Alexa for Business). Inline policies attached to permission
sets are worth reviewing, as they can add permissions or restrict them, and
they're easy to miss if you're only looking at the managed policy name.

*Multiple assignments for the same user*: ~iamtestuser1~ appears twice: once with
~AdministratorAccess~ and once with ~Billing~. This isn't automatically a problem,
but a user with both full administrative access and explicit billing access is
worth confirming with IT.

* Common Exceptions and False Positives

*Break-glass accounts*: Most organizations maintain at least one emergency account
with direct ~AdministratorAccess~ that bypasses normal access controls. A direct
USER assignment to ~AdministratorAccess~ may be intentional for this reason. Ask
IT whether a break-glass account exists, confirm the username matches, and
document it as an accepted exception if appropriate.

*Small organizations or early-stage environments*: Some teams haven't implemented
group-based access management yet and assign permissions directly to users
across the board. This isn't a false positive, it's a control gap, but the
finding should reflect the scale and maturity of the environment. A two-person
startup with direct assignments is a different risk than an enterprise doing the
same thing.

*Service or automation accounts*: Occasionally a USER principal in Identity Center
is a service account rather than a human. These may legitimately have specific
permission sets assigned directly. Confirm the account's purpose before writing
it up.

* How to Write Up the Finding

If you identify a direct high-privilege user assignment that isn't a documented
exception, here's how to frame it:

*Condition:* User ~iamtestuser1~ is directly assigned the ~AdministratorAccess~
permission set in account ~cmc~, rather than receiving access through a group
assignment.

*Criteria:* Access to AWS accounts via IAM Identity Center should be provisioned
through groups to ensure consistent access management. Direct user assignments
bypass group-based controls and are not subject to standard group membership
reviews.

*Risk:* Direct user assignments increase the likelihood of orphaned access
following role changes or departures. They are also harder to identify during
periodic access reviews, as reviewers may focus on group membership rather than
individual assignments.

*Evidence:* Attach the relevant portion of ~report_cmc.json~ filtered to show the
specific principal, permission set, and policies. The JSON output is
self-documenting, as it includes the account name in the filename and contains
the full policy details alongside the assignment.

To filter the output to just the direct user assignments for the evidence
attachment:

#+begin_src bash
jq '[.[] | select(.principal.type == "USER")]' report_cmc.json
#+end_src

#+caption: Filtered User Assignments
#+attr_html: :alt Terminal output of the jq filter showing only direct user assignments from report_cmc.json.
[[https://img.cleberg.net/blog/20260221-auditing-aws-iam/jq.webp]]