keyword.py

"""
This code was extracted in part from
https://github.com/PyCQA/bandit. Using similar heuristic logic,
we adapted it to fit our plugin infrastructure, to create an organized,
concerted effort in detecting all type of secrets in code.

Copyright (c) 2014 Hewlett-Packard Development Company, L.P.

Permission is hereby granted, free of charge, to any person obtaining a copy
of this software and associated documentation files (the "Software"), to deal
in the Software without restriction, including without limitation the rights
to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the Software is
furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in
all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
THE SOFTWARE.
"""
import re
from typing import Dict
from typing import Generator
from typing import Optional
from typing import Pattern
from typing import Set

from ..core.potential_secret import PotentialSecret
from ..util.filetype import determine_file_type
from ..util.filetype import FileType
from .base import BasePlugin


# Note: All values here should be lowercase
DENYLIST = (
    'apikey',
    'api_key',
    'aws_secret_access_key',
    'db_pass',
    'password',
    'passwd',
    'private_key',
    'secret',
    'secrete',
)
FALSE_POSITIVES = {
    '""',
    '""):',
    '"\'',
    '")',
    '"dummy',
    '"replace',
    '"this',
    '#pass',
    '#password',
    '$(shell',
    "'\"",
    "''",
    "''):",
    "')",
    "'dummy",
    "'replace",
    "'this",
    '(nsstring',
    '-default}',
    '::',
    '<%=',
    '<?php',
    '<a',
    '<aws_secret_access_key>',
    '<input',
    '<password>',
    '<redacted>',
    '<secret',
    '>',
    '=',
    '\\"$(shell',
    '\\k.*"',
    "\\k.*'",
    '`cat',
    '`grep',
    '`sudo',
    'account_password',
    'api_key',
    'disable',
    'dummy_secret',
    'dummy_value',
    'false',
    'false):',
    'false,',
    'false;',
    'login_password',
    'none',
    'none,',
    'none}',
    'nopasswd',
    'not',
    'not_real_key',
    'null',
    'null,',
    'null.*"',
    "null.*'",
    'null;',
    'pass',
    'pass)',
    'password',
    'password)',
    'password))',
    'password,',
    'password},',
    'prompt',
    'redacted',
    'secret',
    'some_key',
    'str',
    'str_to_sign',
    'string',
    'string)',
    'string,',
    'string;',
    'string?',
    'string?)',
    'string}',
    'string}}',
    'test',
    'test-access-key',
    'thisisnottherealsecret',
    'todo',
    'true',
    'true):',
    'true,',
    'true;',
    'undef',
    'undef,',
    '{',
    '{{',
}
# Includes ], ', " as closing
CLOSING = r'[]\'"]{0,2}'
DENYLIST_REGEX = r'|'.join(DENYLIST)
# Non-greedy match
OPTIONAL_WHITESPACE = r'\s*?'
OPTIONAL_NON_WHITESPACE = r'[^\s]*?'
QUOTE = r'[\'"]'
SECRET = r'[^\s]+'
SQUARE_BRACKETS = r'(\[\])'

FOLLOWED_BY_COLON_EQUAL_SIGNS_REGEX = re.compile(
    # e.g. my_password := "bar" or my_password := bar
    r'({denylist})({closing})?{whitespace}:=?{whitespace}({quote}?)({secret})(\3)'.format(
        denylist=DENYLIST_REGEX,
        closing=CLOSING,
        quote=QUOTE,
        whitespace=OPTIONAL_WHITESPACE,
        secret=SECRET,
    ),
)
FOLLOWED_BY_COLON_REGEX = re.compile(
    # e.g. api_key: foo
    r'({denylist})({closing})?:{whitespace}({quote}?)({secret})(\3)'.format(
        denylist=DENYLIST_REGEX,
        closing=CLOSING,
        quote=QUOTE,
        whitespace=OPTIONAL_WHITESPACE,
        secret=SECRET,
    ),
)
FOLLOWED_BY_COLON_QUOTES_REQUIRED_REGEX = re.compile(
    # e.g. api_key: "foo"
    r'({denylist})({closing})?:({whitespace})({quote})({secret})(\4)'.format(
        denylist=DENYLIST_REGEX,
        closing=CLOSING,
        quote=QUOTE,
        whitespace=OPTIONAL_WHITESPACE,
        secret=SECRET,
    ),
)
FOLLOWED_BY_EQUAL_SIGNS_OPTIONAL_BRACKETS_OPTIONAL_AT_SIGN_QUOTES_REQUIRED_REGEX = re.compile(
    # e.g. my_password = "bar"
    # e.g. my_password = @"bar"
    # e.g. my_password[] = "bar";
    r'({denylist})({square_brackets})?{optional_whitespace}={optional_whitespace}(@)?(")({secret})(\5)'.format(  # noqa: E501
        denylist=DENYLIST_REGEX,
        square_brackets=SQUARE_BRACKETS,
        optional_whitespace=OPTIONAL_WHITESPACE,
        secret=SECRET,
    ),
)
FOLLOWED_BY_EQUAL_SIGNS_REGEX = re.compile(
    # e.g. my_password = bar
    r'({denylist})({closing})?{whitespace}={whitespace}({quote}?)({secret})(\3)'.format(
        denylist=DENYLIST_REGEX,
        closing=CLOSING,
        quote=QUOTE,
        whitespace=OPTIONAL_WHITESPACE,
        secret=SECRET,
    ),
)
FOLLOWED_BY_EQUAL_SIGNS_QUOTES_REQUIRED_REGEX = re.compile(
    # e.g. my_password = "bar"
    r'({denylist})({closing})?{whitespace}={whitespace}({quote})({secret})(\3)'.format(
        denylist=DENYLIST_REGEX,
        closing=CLOSING,
        quote=QUOTE,
        whitespace=OPTIONAL_WHITESPACE,
        secret=SECRET,
    ),
)
FOLLOWED_BY_QUOTES_AND_SEMICOLON_REGEX = re.compile(
    # e.g. private_key "something";
    r'({denylist}){nonWhitespace}{whitespace}({quote})({secret})(\2);'.format(
        denylist=DENYLIST_REGEX,
        nonWhitespace=OPTIONAL_NON_WHITESPACE,
        quote=QUOTE,
        whitespace=OPTIONAL_WHITESPACE,
        secret=SECRET,
    ),
)
DENYLIST_REGEX_TO_GROUP = {
    FOLLOWED_BY_COLON_REGEX: 4,
    FOLLOWED_BY_EQUAL_SIGNS_REGEX: 4,
    FOLLOWED_BY_QUOTES_AND_SEMICOLON_REGEX: 3,
}
GOLANG_DENYLIST_REGEX_TO_GROUP = {
    FOLLOWED_BY_COLON_EQUAL_SIGNS_REGEX: 4,
    FOLLOWED_BY_EQUAL_SIGNS_REGEX: 4,
    FOLLOWED_BY_QUOTES_AND_SEMICOLON_REGEX: 3,
}
OBJECTIVE_C_DENYLIST_REGEX_TO_GROUP = {
    FOLLOWED_BY_EQUAL_SIGNS_OPTIONAL_BRACKETS_OPTIONAL_AT_SIGN_QUOTES_REQUIRED_REGEX: 6,
}
QUOTES_REQUIRED_DENYLIST_REGEX_TO_GROUP = {
    FOLLOWED_BY_COLON_QUOTES_REQUIRED_REGEX: 5,
    FOLLOWED_BY_EQUAL_SIGNS_QUOTES_REQUIRED_REGEX: 4,
    FOLLOWED_BY_QUOTES_AND_SEMICOLON_REGEX: 3,
}
QUOTES_REQUIRED_FILETYPES = {
    FileType.CLS,
    FileType.JAVA,
    FileType.JAVASCRIPT,
    FileType.PYTHON,
    FileType.SWIFT,
    FileType.TERRAFORM,
}


class KeywordDetector(BasePlugin):
    """
    Scans for secret-sounding variable names.

    This checks if denylisted keywords are present in the analyzed string.
    """
    secret_type = 'Secret Keyword'

    def __init__(self, keyword_exclude: Optional[str] = None) -> None:
        self.keyword_exclude = None
        if keyword_exclude:
            self.keyword_exclude = re.compile(
                keyword_exclude,
                re.IGNORECASE,
            )

    def analyze_string(
        self,
        string: str,
        denylist_regex_to_group: Optional[Dict[Pattern, int]] = None,
    ) -> Generator[str, None, None]:
        if self.keyword_exclude and self.keyword_exclude.search(string):
            return

        if denylist_regex_to_group is None:
            attempts = [
                QUOTES_REQUIRED_DENYLIST_REGEX_TO_GROUP,
                DENYLIST_REGEX_TO_GROUP,
            ]
        else:
            attempts = [denylist_regex_to_group]

        has_results = False
        for denylist_regex_to_group in attempts:
            for denylist_regex, group_number in denylist_regex_to_group.items():
                match = denylist_regex.search(string)
                if match:
                    has_results = True
                    yield match.group(group_number)

            if has_results:
                break

    def analyze_line(self, filename: str, line: str, line_number: int = 0) -> Set[PotentialSecret]:
        filetype = determine_file_type(filename)

        if filetype in QUOTES_REQUIRED_FILETYPES:
            denylist_regex_to_group = QUOTES_REQUIRED_DENYLIST_REGEX_TO_GROUP
        elif filetype == FileType.GO:
            denylist_regex_to_group = GOLANG_DENYLIST_REGEX_TO_GROUP
        elif filetype == FileType.OBJECTIVE_C:
            denylist_regex_to_group = OBJECTIVE_C_DENYLIST_REGEX_TO_GROUP
        else:
            denylist_regex_to_group = DENYLIST_REGEX_TO_GROUP

        return super().analyze_line(
            filename=filename,
            line=line,
            line_number=line_number,
            denylist_regex_to_group=denylist_regex_to_group,
        )

    @property
    def json(self):
        return {
            'keyword_exclude': (
                self.keyword_exclude.pattern
                if self.keyword_exclude
                else '',
            ),
            **super().json(),
        }


def probably_false_positive(lowered_secret, filetype):
    # TODO: Move this to filters/*
    if (
        any(
            false_positive in lowered_secret
            for false_positive in (
                '/etc/',
                'fake',
                'forgot',
            )
        ) or lowered_secret in FALSE_POSITIVES
        # For e.g. private_key "some/dir/that/is/not/a/secret";
        or lowered_secret.count('/') >= 3
        # For e.g. "secret": "{secret}"
        or (
            lowered_secret[0] == '{'
            and lowered_secret[-1] == '}'
        ) or (
            filetype not in QUOTES_REQUIRED_FILETYPES
            and lowered_secret[0] == '$'
        ) or (
            filetype == FileType.EXAMPLE
            and lowered_secret[0] == '<'
            and lowered_secret[-1] == '>'
        )
    ):
        return True

    # Heuristic for no function calls
    try:
        if (
            lowered_secret.index('(') < lowered_secret.index(')')
        ):
            return True
    except ValueError:
        pass

    # Heuristic for e.g. request.json_body['hey']
    try:
        if (
            lowered_secret.index('[') < lowered_secret.index(']')
        ):
            return True
    except ValueError:
        pass

    # Heuristic for e.g. ${link}
    try:
        if (
            lowered_secret.index('${') < lowered_secret.index('}')
        ):
            return True
    except ValueError:
        pass

    return False