Group with privilege escalation by actions 'iam:UpdateAssumeRolePolicy' and 'sts:AssumeRole'

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Metadata

Id: terraform-aws-group-with-privilege-escalation-by-actions-iam-updateassumerolepolicy-and-sts-assumerole

Provider: AWS

Platform: Terraform

Severity: Medium

Category: Access Control

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Description

This check identifies IAM groups that have been granted both the iam:UpdateAssumeRolePolicy and sts:AssumeRole actions with a wildcard resource ("Resource": "*") in their attached policies. Granting these permissions together allows any user in the group to escalate their privileges by altering assume role policies and then assuming any role, potentially gaining unauthorized access to sensitive resources. If left unaddressed, this misconfiguration could enable attackers or malicious insiders to escalate permissions, compromise account security, and move laterally throughout your AWS environment.

Compliant Code Examples

# Has iam:UpdateAssumeRolePolicy but no sts:AssumeRole grant: only one of
# the two required permissions is present.
resource "aws_iam_group" "cosmic2" {
  name = "cosmic2"
}

resource "aws_iam_group_policy" "update_assume_role_only" {
  name  = "update_assume_role_only"
  group = aws_iam_group.cosmic2.name

  policy = jsonencode({
    Version = "2012-10-17"
    Statement = [
      {
        Action = [
          "iam:UpdateAssumeRolePolicy",
        ]
        Effect   = "Allow"
        Resource = "*"
      },
    ]
  })
}

# Has sts:AssumeRole but no iam:UpdateAssumeRolePolicy grant: only one of
# the two required permissions is present.
resource "aws_iam_group" "cosmic3" {
  name = "cosmic3"
}

resource "aws_iam_group_policy" "assume_role_only" {
  name  = "assume_role_only"
  group = aws_iam_group.cosmic3.name

  policy = jsonencode({
    Version = "2012-10-17"
    Statement = [
      {
        Action = [
          "sts:AssumeRole",
        ]
        Effect   = "Allow"
        Resource = "*"
      },
    ]
  })
}

Non-Compliant Code Examples

resource "aws_iam_group" "cosmic" {
  name = "cosmic"
}

resource "aws_iam_group_policy" "test_inline_policy" {
  name = "test_inline_policy"
  group = aws_iam_group.cosmic.name

  policy = jsonencode({
    Version = "2012-10-17"
    Statement = [
      {
        Action = [
          "iam:UpdateAssumeRolePolicy",
        ]
        Effect   = "Allow"
        Resource = "*"
      },
    ]
  })
}


resource "aws_iam_policy_attachment" "test-attach" {
  name       = "test-attachment"
  groups     = [aws_iam_group.cosmic.name]
  policy_arn = aws_iam_policy.policy.arn
}


resource "aws_iam_policy" "policy" {
  name        = "test-policy"
  description = "A test policy"

  policy = jsonencode({
    Version = "2012-10-17"
    Statement = [
      {
        Action = [
          "sts:AssumeRole",
        ]
        Effect   = "Allow"
        Resource = "*"
      },
    ]
  })
}

resource "aws_iam_group" "nebula" {
  name = "nebula"
}

resource "aws_iam_group_policy" "update_assume_role_policy" {
  name  = "update_assume_role_policy"
  group = aws_iam_group.nebula.name

  policy = jsonencode({
    Version = "2012-10-17"
    Statement = [
      {
        Action = [
          "iam:UpdateAssumeRolePolicy",
        ]
        Effect   = "Allow"
        Resource = "*"
      },
    ]
  })
}

resource "aws_iam_group_policy" "assume_role_policy" {
  name  = "assume_role_policy"
  group = aws_iam_group.nebula.name

  policy = jsonencode({
    Version = "2012-10-17"
    Statement = [
      {
        Action = [
          "sts:AssumeRole",
        ]
        Effect   = "Allow"
        Resource = "*"
      },
    ]
  })
}