# AWS - STS Privesc

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## STS

### `sts:AssumeRole`

Every role is created with a **role trust policy**, this policy indicates **who can assume the created role**. If a role from the **same account** says that an account can assume it, it means that the account will be able to access the role (and potentially **privesc**).

For example, the following role trust policy indicates that anyone can assume it, therefore **any user will be able to privesc** to the permissions associated with that role.

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

You can impersonate a role running:

```bash
aws sts assume-role --role-arn $ROLE_ARN --role-session-name sessionname
```

**Potential Impact:** Privesc to the role.

> [!CAUTION]
> Note that in this case the permission `sts:AssumeRole` needs to be **indicated in the role to abuse** and not in a policy belonging to the attacker.\
> With one exception, in order to **assume a role from a different account** the attacker account **also needs** to have the **`sts:AssumeRole`** over the role.


### `sts:AssumeRoleWithSAML`

A trust policy with this role grants **users authenticated via SAML access to impersonate the role.**

An example of a trust policy with this permission is:

```json
{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Sid": "OneLogin",
      "Effect": "Allow",
      "Principal": {
        "Federated": "arn:aws:iam::290594632123:saml-provider/OneLogin"
      },
      "Action": "sts:AssumeRoleWithSAML",
      "Condition": {
        "StringEquals": {
          "SAML:aud": "https://signin.aws.amazon.com/saml"
        }
      }
    }
  ]
}
```

To generate credentials to impersonate the role in general you could use something like:

```bash
aws sts assume-role-with-saml --role-arn <role_arn> --principal-arn <provider_arn> --saml-assertion <base64_saml_response>
```

But **providers** might have their **own tools** to make this easier, like [onelogin-aws-assume-role](https://github.com/onelogin/onelogin-python-aws-assume-role):

```bash
onelogin-aws-assume-role --onelogin-subdomain mettle --onelogin-app-id 283740 --aws-region eu-west-1 -z 3600
```

**Potential Impact:** Privesc to the role.

### `sts:AssumeRoleWithWebIdentity`

This permission grants permission to obtain a set of temporary security credentials for **users who have been authenticated in a mobile, web application, EKS...** with a web identity provider. [Learn more here.](https://docs.aws.amazon.com/STS/latest/APIReference/API_AssumeRoleWithWebIdentity.html)

For example, if an **EKS service account** should be able to **impersonate an IAM role**, it will have a token in **`/var/run/secrets/eks.amazonaws.com/serviceaccount/token`** and can **assume the role and get credentials** doing something like:

```bash
aws sts assume-role-with-web-identity --role-arn arn:aws:iam::123456789098:role/<role_name> --role-session-name something --web-identity-token file:///var/run/secrets/eks.amazonaws.com/serviceaccount/token
# The role name can be found in the metadata of the configuration of the pod
```

### Federation Abuse

{{#ref}}
../../aws-basic-information/aws-federation-abuse.md
{{#endref}}

### IAM Roles Anywhere Privesc

AWS IAM RolesAnywhere allows workloads outside AWS to assume IAM roles using X.509 certificates. But when trust policies aren't properly scoped, they can be abused for privilege escalation.

To understand this attack, it is necessary to explain what a trust anchor is. A trust anchor in AWS IAM Roles Anywhere is the root of trust entity, it contains the public certificate of a Certificate Authority (CA) that is registered in the account so that AWS can validate the presented X.509 certificates. In this way, if the client certificate was issued by that CA and the trust anchor is active, AWS recognizes it as valid.

In addition, a profile is the configuration that defines which attributes of the X.509 certificate (such as CN, OU, or SAN) will be transformed into session tags, and these tags will later be compared against the conditions of the trust policy.

This policy lacks restrictions on which trust anchor or certificate attributes are allowed. As a result, any certificate tied to any trust anchor in the account can be used to assume this role.

```json
{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Effect": "Allow",
      "Principal": {
        "Service": "rolesanywhere.amazonaws.com"
      },
      "Action": [
        "sts:AssumeRole",
        "sts:SetSourceIdentity",
        "sts:TagSession"
      ]
    }
  ]
}

```

To privesc, the `aws_signing_helper` is required from https://docs.aws.amazon.com/rolesanywhere/latest/userguide/credential-helper.html

Then using a valid certificate the attacker can pivot into the higher privilege role 

```bash
aws_signing_helper credential-process \
  --certificate readonly.pem \
  --private-key readonly.key \
  --trust-anchor-arn arn:aws:rolesanywhere:us-east-1:123456789012:trust-anchor/ta-id \
  --profile-arn arn:aws:rolesanywhere:us-east-1:123456789012:profile/default \
  --role-arn arn:aws:iam::123456789012:role/Admin
```

The trust anchor validates that the client’s `readonly.pem` certificate comes from its authorized CA, and within this `readonly.pem` certificate is the public key that AWS uses to verify that the signature was made with its corresponding private key `readonly.key`.

The certificate also provides attributes (such as CN or OU) that the `default` profile transforms into tags, which the role’s trust policy can use to decide whether to authorize access. If there are no conditions in the trust policy, those tags have no use, and access is granted to anyone with a valid certificate.

For this attack to be possible, both the trust anchor and the `default` profile must be active.

### References

- [https://www.ruse.tech/blogs/aws-roles-anywhere-privilege-escalation](https://www.ruse.tech/blogs/aws-roles-anywhere-privilege-escalation)

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