AWS - IAM Post Exploitation

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IAM

For more information about IAM access:

AWS - IAM, Identity Center & SSO Enum

Confused Deputy Problem

If you allow an external account (A) to access a role in your account, you will probably have 0 visibility on who can exactly access that external account. This is a problem, because if another external account (B) can access the external account (A) it's possible that B will also be able to access your account.

Therefore, when allowing an external account to access a role in your account it's possible to specify an ExternalId. This is a "secret" string that the external account (A) need to specify in order to assume the role in your organization. As the external account B won't know this string, even if he has access over A he won't be able to access your role.

However, note that this ExternalId "secret" is not a secret, anyone that can read the IAM assume role policy will be able to see it. But as long as the external account A knows it, but the external account B doesn't know it, it prevents B abusing A to access your role.

Example:

{
  "Version": "2012-10-17",
  "Statement": {
    "Effect": "Allow",
    "Principal": {
      "AWS": "Example Corp's AWS Account ID"
    },
    "Action": "sts:AssumeRole",
    "Condition": {
      "StringEquals": {
        "sts:ExternalId": "12345"
      }
    }
  }
}

Unexpected Trusts

Wildcard as principal

{
  "Action": "sts:AssumeRole",
  "Effect": "Allow",
  "Principal": { "AWS": "*" }
}

This policy allows all AWS to assume the role.

Service as principal

{
  "Action": "lambda:InvokeFunction",
  "Effect": "Allow",
  "Principal": { "Service": "apigateway.amazonaws.com" },
  "Resource": "arn:aws:lambda:000000000000:function:foo"
}

This policy allows any account to configure their apigateway to call this Lambda.

S3 as principal

"Condition": {
"ArnLike": { "aws:SourceArn": "arn:aws:s3:::source-bucket" },
    "StringEquals": {
        "aws:SourceAccount": "123456789012"
    }
}

If an S3 bucket is given as a principal, because S3 buckets do not have an Account ID, if you deleted your bucket and the attacker created it in their own account, then they could abuse this.

Not supported

{
  "Effect": "Allow",
  "Principal": { "Service": "cloudtrail.amazonaws.com" },
  "Action": "s3:PutObject",
  "Resource": "arn:aws:s3:::myBucketName/AWSLogs/MY_ACCOUNT_ID/*"
}

A common way to avoid Confused Deputy problems is the use of a condition with AWS:SourceArn to check the origin ARN. However, some services might not support that (like CloudTrail according to some sources).

Credential Deletion

With any of the following permissions — iam:DeleteAccessKey, iam:DeleteLoginProfile, iam:DeleteSSHPublicKey, iam:DeleteServiceSpecificCredential, iam:DeleteInstanceProfile, iam:DeleteServerCertificate, iam:DeleteCloudFrontPublicKey, iam:RemoveRoleFromInstanceProfile — an actor can remove access keys, login profiles, SSH keys, service-specific credentials, instance profiles, certificates or CloudFront public keys, or disassociate roles from instance profiles. Such actions can immediately block legitimate users and applications and cause denial-of-service or loss of access for systems that depend on those credentials, so these IAM permissions must be tightly restricted and monitored.

# Remove Access Key of a user
aws iam delete-access-key \
  --user-name <Username> \
  --access-key-id AKIAIOSFODNN7EXAMPLE

## Remove ssh key of a user
aws iam delete-ssh-public-key \
  --user-name <Username> \
  --ssh-public-key-id APKAEIBAERJR2EXAMPLE

Identity Deletion

With permissions like iam:DeleteUser, iam:DeleteGroup, iam:DeleteRole, or iam:RemoveUserFromGroup, an actor can delete users, roles, or groups—or change group membership—removing identities and associated traces. This can immediately break access for people and services that depend on those identities, causing denial-of-service or loss of access, so these IAM actions must be tightly restricted and monitored.

# Delete a user
aws iam delete-user \
  --user-name <Username>

# Delete a group
aws iam delete-group \
  --group-name <Username>

# Delete a role
aws iam delete-role \
  --role-name <Role>

With any of the following permissions — iam:DeleteGroupPolicy, iam:DeleteRolePolicy, iam:DeleteUserPolicy, iam:DeletePolicy, iam:DeletePolicyVersion, iam:DeleteRolePermissionsBoundary, iam:DeleteUserPermissionsBoundary, iam:DetachGroupPolicy, iam:DetachRolePolicy, iam:DetachUserPolicy — an actor can delete or detach managed/inline policies, remove policy versions or permissions boundaries, and unlink policies from users, groups, or roles. This destroys authorizations and can alter the permissions model, causing immediate loss of access or denial-of-service for principals that depended on those policies, so these IAM actions must be tightly restricted and monitored.

# Delete a group policy
aws iam delete-group-policy \
  --group-name <GroupName> \
  --policy-name <PolicyName>

# Delete a role policy
aws iam delete-role-policy \
  --role-name <RoleName> \
  --policy-name <PolicyName>

Federated Identity Deletion

With iam:DeleteOpenIDConnectProvider, iam:DeleteSAMLProvider, and iam:RemoveClientIDFromOpenIDConnectProvider, an actor can delete OIDC/SAML identity providers or remove client IDs. This breaks federated authentication, preventing token validation and immediately denying access to users and services that rely on SSO until the IdP or configurations are restored.

# Delete OIDCP provider
aws iam delete-open-id-connect-provider \
  --open-id-connect-provider-arn arn:aws:iam::111122223333:oidc-provider/accounts.google.com

# Delete SAML provider
aws iam delete-saml-provider \
  --saml-provider-arn arn:aws:iam::111122223333:saml-provider/CorporateADFS

Illegitimate MFA Activation

With iam:EnableMFADevice, an actor can register an MFA device on a user’s identity, preventing the legitimate user from signing in. Once an unauthorized MFA is enabled the user can be locked out until the device is removed or reset (note: if multiple MFA devices are registered, sign-in requires only one, so this attack will have no effect on denying access).

aws iam enable-mfa-device \
  --user-name <Username> \
  --serial-number arn:aws:iam::111122223333:mfa/alice \
  --authentication-code1 123456 \
  --authentication-code2 789012

Certificate/Key Metadata Tampering

With iam:UpdateSSHPublicKey, iam:UpdateCloudFrontPublicKey, iam:UpdateSigningCertificate, iam:UpdateServerCertificate, an actor can change status or metadata of public keys and certificates. By marking keys/certificates inactive or altering references, they can break SSH authentication, invalidate X.509/TLS validations, and immediately disrupt services that depend on those credentials, causing loss of access or availability.

aws iam update-ssh-public-key \
  --user-name <Username> \
  --ssh-public-key-id APKAEIBAERJR2EXAMPLE \
  --status Inactive

aws iam update-server-certificate \
  --server-certificate-name <Certificate_Name> \
  --new-path /prod/

References

• https://docs.aws.amazon.com/IAM/latest/UserGuide/confused-deputy.html