Scan Multiple AWS accounts via AssumeRole (#172)

Add `create-multi-account-config-file` and `scan-multi-account` commands.

Author: kmcquade

.gitignore

@@ -13,6 +13,7 @@ iam-findings-example.json
 private/*
 current.json
 TODO.md
+/private-multi-account-config.yml
 
 venv
 Pipfile.lock

README.md

@@ -80,22 +80,22 @@ Cloudsplaining identifies violations of least privilege in AWS IAM policies and
 
 ## Installation
 
-* Homebrew
+#### Homebrew
 
 ```bash
 brew tap salesforce/cloudsplaining https://github.com/salesforce/cloudsplaining
 brew install cloudsplaining
 ```
 
-* Pip3
+#### Pip3
 
 ```bash
 pip3 install --user cloudsplaining
 ```
 
 * Now you should be able to execute `cloudsplaining` from command line by running `cloudsplaining --help`.
 
-* Shell completion
+#### Shell completion
 
 To enable Bash completion, put this in your `.bashrc`:
 
@@ -279,6 +279,56 @@ Now when you run the `scan` command, you can use the exclusions file like this:
 cloudsplaining scan --exclusions-file exclusions.yml --input-file examples/files/example.json --output examples/files/
 ```
 
+### Scanning Multiple AWS Accounts
+
+If your IAM user or IAM role has `sts:AssumeRole` permissions to a common IAM role across multiple AWS accounts, you can use the `scan-multi-account` command.
+
+This diagram depicts how the process works:
+
+![Diagram for scanning multiple AWS accounts with Cloudsplaining](docs/_images/scan-multiple-accounts.png)
+
+
+> Note: If you are new to setting up cross-account access, check out [the official AWS Tutorial on Delegating access across AWS accounts using IAM roles](https://docs.aws.amazon.com/IAM/latest/UserGuide/tutorial_cross-account-with-roles.html). That can help you set up the architecture above.
+
+
+* First, you'll need to create the multi-account config file. Run the following command:
+
+```bash
+cloudsplaining create-multi-account-config-file \ 
+    -o multi-account-config.yml
+```
+
+* This will generate a file called `multi-account-config.yml` with the following contents:
+
+```yaml
+accounts:
+  default_account: 123456789012
+  prod: 123456789013
+  test: 123456789014
+```
+
+!!! note 
+    Observe how the format of the file above includes `account_name: accountID`. Edit the file contents to match your desired account name and account ID. Include as many account IDs as you like.
+
+
+For the next step, let's say that:
+ * We have a role in the target accounts that is called `CommonSecurityRole`. 
+* The credentials for your IAM user are under the AWS Credentials profile called `scanning-user`.
+* That user has `sts:AssumeRole` permissions to assume the `CommonSecurityRole` in all your target accounts specified in the YAML file we created previously.
+* You want to save the output to an S3 bucket called `my-results-bucket`
+
+Using the data above, you can run the following command:
+
+```bash
+cloudsplaining scan-multi-account \
+    -c multi-account-config.yml \
+    --profile scanning-user \
+    --role-name CommonSecurityRole \ 
+    --output-bucket my-results-bucket
+```
+
+> Note that if you run the above without the `--profile` flag, it will execute in the standard [AWS Credentials order of precedence](https://docs.aws.amazon.com/sdk-for-java/v1/developer-guide/credentials.html#credentials-default) (i.e., Environment variables, credentials profiles, ECS container credentials, then finally EC2 Instance Profile credentials). 
+
 
 ## Cheatsheet
 
@@ -316,7 +366,7 @@ This is likely an issue with your PATH. Your PATH environment variable is not co
 export PATH=$HOME/Library/Python/3.7/bin/:$PATH
 ```
 
-**I followed the installation instructions but I am receiving a `ModuleNotFoundError` that says `No module named policy_sentry.analysis.expand`. What should I do?**
+**I followed the installation instructions, but I am receiving a `ModuleNotFoundError` that says `No module named policy_sentry.analysis.expand`. What should I do?**
 
 Try upgrading to the latest version of Cloudsplaining. This error was fixed in version 0.0.10.
 

cloudsplaining/__init__.py

@@ -24,3 +24,50 @@
 def change_log_level(log_level):
     """"Change log level of module logger"""
     logger.setLevel(log_level)
+
+
+def set_stream_logger(name="cloudsplaining", level=logging.DEBUG, format_string=None):  # pylint: disable=redefined-outer-name
+    """
+    Add a stream handler for the given name and level to the logging module.
+    By default, this logs all cloudsplaining messages to ``stdout``.
+        >>> import cloudsplaining
+        >>> cloudsplaining.set_stream_logger('cloudsplaining.scan', logging.INFO)
+    :type name: string
+    :param name: Log name
+    :type level: int
+    :param level: Logging level, e.g. ``logging.INFO``
+    :type format_string: str
+    :param format_string: Log message format
+    """
+    # remove existing handlers. since NullHandler is added by default
+    handlers = logging.getLogger(name).handlers
+    for handler in handlers:  # pylint: disable=redefined-outer-name
+        logging.getLogger(name).removeHandler(handler)
+    if format_string is None:
+        format_string = "%(asctime)s %(name)s [%(levelname)s] %(message)s"
+    logger = logging.getLogger(name)  # pylint: disable=redefined-outer-name
+    logger.setLevel(level)
+    handler = logging.StreamHandler()  # pylint: disable=redefined-outer-name
+    handler.setLevel(level)
+    formatter = logging.Formatter(format_string)  # pylint: disable=redefined-outer-name
+    handler.setFormatter(formatter)
+    logger.addHandler(handler)
+
+
+def set_log_level(verbose):
+    """
+    Set Log Level based on click's count argument.
+
+    Default log level to critical; otherwise, set to: warning for -v, info for -vv, debug for -vvv
+
+    :param verbose: integer for verbosity count.
+    :return:
+    """
+    if verbose == 1:
+        set_stream_logger(level=getattr(logging, "WARNING"))
+    elif verbose == 2:
+        set_stream_logger(level=getattr(logging, "INFO"))
+    elif verbose >= 3:
+        set_stream_logger(level=getattr(logging, "DEBUG"))
+    else:
+        set_stream_logger(level=getattr(logging, "CRITICAL"))

cloudsplaining/bin/cli.py

@@ -21,8 +21,10 @@ def cloudsplaining():
 
 
 cloudsplaining.add_command(command.create_exclusions_file.create_exclusions_file)
+cloudsplaining.add_command(command.create_multi_account_config_file.create_multi_account_config_file)
 cloudsplaining.add_command(command.expand_policy.expand_policy)
 cloudsplaining.add_command(command.scan.scan)
+cloudsplaining.add_command(command.scan_multi_account.scan_multi_account)
 cloudsplaining.add_command(command.scan_policy_file.scan_policy_file)
 cloudsplaining.add_command(command.download.download)
 

cloudsplaining/bin/version.py

@@ -1,2 +1,2 @@
 # pylint: disable=missing-module-docstring
-__version__ = "0.3.2"
+__version__ = "0.4.0"

cloudsplaining/command/__init__.py

@@ -1,6 +1,8 @@
 # pylint: disable=missing-module-docstring
 from cloudsplaining.command import create_exclusions_file
+from cloudsplaining.command import create_multi_account_config_file
 from cloudsplaining.command import expand_policy
 from cloudsplaining.command import download
 from cloudsplaining.command import scan
+from cloudsplaining.command import scan_multi_account
 from cloudsplaining.command import scan_policy_file

cloudsplaining/command/create_exclusions_file.py

@@ -13,6 +13,7 @@
 import click
 from cloudsplaining.shared.constants import EXCLUSIONS_TEMPLATE
 from cloudsplaining import change_log_level
+from cloudsplaining.shared import utils
 
 logger = logging.getLogger(__name__)
 
@@ -48,7 +49,7 @@ def create_exclusions_file(output_file, verbose):
     with open(filename, "a") as file_obj:
         for line in EXCLUSIONS_TEMPLATE:
             file_obj.write(line)
-    print(f"Exclusions template file written to: {filename}")
+    utils.print_green(f"Success! Exclusions template file written to: {filename}")
     print(
         "Make sure you download your account authorization details before running the scan. Set your AWS access keys as environment variables then run: "
     )

cloudsplaining/command/create_multi_account_config_file.py

@@ -0,0 +1,65 @@
+"""
+Create YML Template files for the exclusions template command.
+This way, users don't have to remember exactly how to phrase the yaml files, since this command creates it for them.
+"""
+# Copyright (c) 2020, salesforce.com, inc.
+# All rights reserved.
+# Licensed under the BSD 3-Clause license.
+# For full license text, see the LICENSE file in the repo root
+# or https://opensource.org/licenses/BSD-3-Clause
+import os
+from pathlib import Path
+import logging
+import click
+from cloudsplaining.shared.constants import MULTI_ACCOUNT_CONFIG_TEMPLATE
+from cloudsplaining import change_log_level
+from cloudsplaining.shared import utils
+
+logger = logging.getLogger(__name__)
+OK_GREEN = "\033[92m"
+END = "\033[0m"
+
+
+@click.command(
+    context_settings=dict(max_content_width=160),
+    short_help="Creates a YML file to be used for multi-account scanning",
+)
+@click.option(
+    "--output-file",
+    "-o",
+    "output_file",
+    type=click.Path(exists=False),
+    default=os.path.join(os.getcwd(), "multi-account-config.yml"),
+    required=True,
+    help="Relative path to output file where we want to store the multi account config template.",
+)
+@click.option(
+    "--verbose",
+    "-v",
+    type=click.Choice(
+        ["critical", "error", "warning", "info", "debug"], case_sensitive=False
+    ),
+)
+def create_multi_account_config_file(output_file, verbose):
+    """
+    Creates a YML file to be used as a multi-account config template, so users can scan many different accounts.
+    """
+    if verbose:
+        log_level = getattr(logging, verbose.upper())
+        change_log_level(log_level)
+    filename = Path(output_file).resolve()
+
+    if os.path.exists(filename):
+        logger.debug("%s exists. Removing the file and replacing its contents.", filename)
+        os.remove(filename)
+
+    with open(filename, "a") as file_obj:
+        for line in MULTI_ACCOUNT_CONFIG_TEMPLATE:
+            file_obj.write(line)
+    utils.print_green(f"Success! Multi-account config file written to: {os.path.relpath(filename)}")
+    print(
+        f"\nMake sure you edit the {os.path.relpath(filename)} file and then run the scan-multi-account command, as shown below."
+    )
+    print(
+        f"\n\tcloudsplaining scan-multi-account --exclusions-file exclusions.yml -c {os.path.relpath(filename)} -o ./"
+    )