pre_commit_hooks/detect_aws_credentials.py

import argparse
import configparser
import os
from typing import List
from typing import NamedTuple
from typing import Optional
from typing import Sequence
from typing import Set


class BadFile(NamedTuple):
    filename: str
    key: str


def get_aws_cred_files_from_env() -> Set[str]:
    """Extract credential file paths from environment variables."""
    return {
        os.environ[env_var]
        for env_var in (
            'AWS_CONFIG_FILE', 'AWS_CREDENTIAL_FILE',
            'AWS_SHARED_CREDENTIALS_FILE', 'BOTO_CONFIG',
        )
        if env_var in os.environ
    }


def get_aws_secrets_from_env() -> Set[str]:
    """Extract AWS secrets from environment variables."""
    keys = set()
    for env_var in (
        'AWS_SECRET_ACCESS_KEY', 'AWS_SECURITY_TOKEN', 'AWS_SESSION_TOKEN',
    ):
        if os.environ.get(env_var):
            keys.add(os.environ[env_var])
    return keys


def get_aws_secrets_from_file(credentials_file: str) -> Set[str]:
    """Extract AWS secrets from configuration files.

    Read an ini-style configuration file and return a set with all found AWS
    secret access keys.
    """
    aws_credentials_file_path = os.path.expanduser(credentials_file)
    if not os.path.exists(aws_credentials_file_path):
        return set()

    parser = configparser.ConfigParser()
    try:
        parser.read(aws_credentials_file_path)
    except configparser.MissingSectionHeaderError:
        return set()

    keys = set()
    for section in parser.sections():
        for var in (
            'aws_secret_access_key', 'aws_security_token',
            'aws_session_token',
        ):
            try:
                key = parser.get(section, var).strip()
                if key:
                    keys.add(key)
            except configparser.NoOptionError:
                pass
    return keys


def check_file_for_aws_keys(
        filenames: Sequence[str],
        keys: Set[bytes],
) -> List[BadFile]:
    """Check if files contain AWS secrets.

    Return a list of all files containing AWS secrets and keys found, with all
    but the first four characters obfuscated to ease debugging.
    """
    bad_files = []

    for filename in filenames:
        with open(filename, 'rb') as content:
            text_body = content.read()
            for key in keys:
                # naively match the entire file, low chance of incorrect
                # collision
                if key in text_body:
                    key_hidden = key.decode()[:4].ljust(28, '*')
                    bad_files.append(BadFile(filename, key_hidden))
    return bad_files


def main(argv: Optional[Sequence[str]] = None) -> int:
    parser = argparse.ArgumentParser()
    parser.add_argument('filenames', nargs='+', help='Filenames to run')
    parser.add_argument(
        '--credentials-file',
        dest='credentials_file',
        action='append',
        default=[
            '~/.aws/config', '~/.aws/credentials', '/etc/boto.cfg', '~/.boto',
        ],
        help=(
            'Location of additional AWS credential file from which to get '
            'secret keys. Can be passed multiple times.'
        ),
    )
    parser.add_argument(
        '--allow-missing-credentials',
        dest='allow_missing_credentials',
        action='store_true',
        help='Allow hook to pass when no credentials are detected.',
    )
    args = parser.parse_args(argv)

    credential_files = set(args.credentials_file)

    # Add the credentials files configured via environment variables to the set
    # of files to to gather AWS secrets from.
    credential_files |= get_aws_cred_files_from_env()

    keys: Set[str] = set()
    for credential_file in credential_files:
        keys |= get_aws_secrets_from_file(credential_file)

    # Secrets might be part of environment variables, so add such secrets to
    # the set of keys.
    keys |= get_aws_secrets_from_env()

    if not keys and args.allow_missing_credentials:
        return 0

    if not keys:
        print(
            'No AWS keys were found in the configured credential files and '
            'environment variables.\nPlease ensure you have the correct '
            'setting for --credentials-file',
        )
        return 2

    keys_b = {key.encode() for key in keys}
    bad_filenames = check_file_for_aws_keys(args.filenames, keys_b)
    if bad_filenames:
        for bad_file in bad_filenames:
            print(f'AWS secret found in {bad_file.filename}: {bad_file.key}')
        return 1
    else:
        return 0


if __name__ == '__main__':
    exit(main())