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Implemented a better date conversion for 'date:' and 'modified:' fields. #297

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Implemented a better date conversion for 'date:' and 'modified:' fields. #297

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Implemented a better date conversion for 'date:' and 'modified:' fields.
Oct 25, 2024
33970e9
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Oct 25, 2024
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66 changes: 42 additions & 24 deletions sigma/rule.py
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Original file line number Diff line number Diff line change
Expand Up @@ -5,6 +5,7 @@
from enum import Enum, auto
from datetime import date, datetime
import yaml
import re
import sigma
from sigma.types import SigmaType, SigmaNull, SigmaString, SigmaNumber, sigma_type
from sigma.modifiers import (
Expand Down Expand Up @@ -847,6 +848,45 @@ class instantiation of an object derived from the SigmaRuleBase class and the er
SigmaRule object. Else the first recognized error is raised as exception.
"""
errors = []

def get_rule_as_date(name: str, exception_class) -> Optional[date]:
"""
Accepted string based date formats are in range 1000-01-01 .. 3999-12-31:
* XXXX-XX-XX -- fully corresponds to yaml date format
* XXXX/XX/XX, XXXX/XX/X, XXXX/X/XX, XXXX/X/X -- often occurs in the US-based sigmas
Not accepted are ambiguous dates such as:
2024-01-1, 24-1-24, 24/1/1, ...
"""
nonlocal errors, rule, source
result = rule.get(name)
if (
result is not None
and not isinstance(result, date)
and not isinstance(result, datetime)
):
error = True
try:
result = str(result) # forcifully convert whatever the type is into string
accepted_regexps = (
"([1-3][0-9][0-9][0-9])-([01][0-9])-([0-3][0-9])", # 1000-01-01 .. 3999-12-31
"([1-3][0-9][0-9][0-9])/([01]?[0-9])/([0-3]?[0-9])", # 1000/1/1, 1000/01/01 .. 3999/12/31
)
for date_regexp in accepted_regexps:
matcher = re.fullmatch(date_regexp, result)
if matcher:
result = date(int(matcher[1]), int(matcher[2]), int(matcher[3]))
error = False
break
except Exception:
pass
if error:
errors.append(
exception_class(
f"Rule {name} '{ result }' is invalid, use yyyy-mm-dd", source=source
)
)
return result

# Rule identifier may be empty or must be valid UUID
rule_id = rule.get("id")
if rule_id is not None:
Expand Down Expand Up @@ -944,32 +984,10 @@ class instantiation of an object derived from the SigmaRuleBase class and the er
)

# parse rule date if existing
rule_date = rule.get("date")
if rule_date is not None:
if not isinstance(rule_date, date) and not isinstance(rule_date, datetime):
try:
rule_date = date(*(int(i) for i in rule_date.split("-")))
except ValueError:
errors.append(
sigma_exceptions.SigmaDateError(
f"Rule date '{ rule_date }' is invalid, must be yyyy-mm-dd",
source=source,
)
)
rule_date = get_rule_as_date("date", sigma_exceptions.SigmaDateError)

# parse rule modified if existing
rule_modified = rule.get("modified")
if rule_modified is not None:
if not isinstance(rule_modified, date) and not isinstance(rule_modified, datetime):
try:
rule_modified = date(*(int(i) for i in rule_modified.split("-")))
except ValueError:
errors.append(
sigma_exceptions.SigmaModifiedError(
f"Rule modified '{ rule_modified }' is invalid, must be yyyy-mm-dd",
source=source,
)
)
rule_modified = get_rule_as_date("modified", sigma_exceptions.SigmaModifiedError)

# Rule fields validation
rule_fields = rule.get("fields")
Expand Down
114 changes: 89 additions & 25 deletions tests/test_rule.py
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Original file line number Diff line number Diff line change
Expand Up @@ -879,15 +879,68 @@ def test_sigmarule_bad_status_type():


def test_sigmarule_bad_date():
with pytest.raises(sigma_exceptions.SigmaDateError, match="Rule date.*test.yml"):
SigmaRule.from_dict({"date": "bad"}, source=sigma_exceptions.SigmaRuleLocation("test.yml"))
"""This test uses string data type as date representation in yaml"""
bad_string_dates = (
"bad",
" 2024-11-24",
"2024-11-24 ",
"2024 11-24",
"24-11-24",
"02-02-02",
"4000-01-01",
"10000-01-01",
"2022-01/01",
"2022/01-01",
)
for test_string in bad_string_dates:
match_string = f"Rule date '{test_string}' is invalid, use yyyy-mm-dd"
with pytest.raises(sigma_exceptions.SigmaDateError, match=match_string) as ex:
SigmaRule.from_yaml(
f"""
title: Test
date: '{test_string}' # try a string
logsource:
product: foobar
detection:
selection_1:
fieldA: valueA
condition: selection_1
"""
)
assert False, f"Did not throw SigmaDateError on date {test_string}"


def test_sigmarule_bad_modified():
with pytest.raises(sigma_exceptions.SigmaModifiedError, match="Rule modified.*test.yml"):
SigmaRule.from_dict(
{"modified": "bad"}, source=sigma_exceptions.SigmaRuleLocation("test.yml")
)
"""
This test uses yaml ability to recognize dates.
Therefore, here 4000-01-01 will be interpreted as a correct yaml date.
"""
bad_dates = (
"bad",
"24-11-24",
"02-02-02",
"2024-5-5",
"10000-01-01",
"2022-01/01",
"2022/01-01",
"2022 01/01",
)
for test_string in bad_dates:
match_string = f"Rule modified '{test_string}' is invalid, use yyyy-mm-dd"
with pytest.raises(sigma_exceptions.SigmaModifiedError, match=match_string) as ex:
SigmaRule.from_yaml(
f"""
title: Test
modified: {test_string} # this can be recognized as date by yaml parser
logsource:
product: foobar
detection:
selection_1:
fieldA: valueA
condition: selection_1
"""
)
assert False, f"Did not throw SigmaModifiedError on date {test_string}"


def test_sigmarule_bad_falsepositives():
Expand Down Expand Up @@ -932,25 +985,36 @@ def test_sigmarule_date():


def test_modified_date():
expected_date = date(3000, 11, 3)
rule = SigmaRule.from_yaml(
"""
title: Test
id: cafedead-beef-0000-1111-0123456789ab
level: medium
status: test
date: 3000-01-02
modified: 3000-11-03
logsource:
product: foobar
detection:
selection_1:
fieldA: valueA
condition: selection_1
"""
)
assert rule is not None
assert rule.modified == expected_date
validDates = {
"3000-12-31": date(3000, 12, 31), # can appear as a generic date in the future
"2999-04-04": date(2999, 4, 4),
"2024-11-22": date(2024, 11, 22),
"1970-01-01": date(1970, 1, 1), # can appear as a generic date in the past
"1900-12-31": date(1900, 12, 31), # not much useful, but correct
"2024/11/22": date(2024, 11, 22), # US-based sigmas have such dates
"2024/1/2": date(2024, 1, 2),
"1970/1/1": date(1970, 1, 1),
}
for test_string, expected_date in validDates.items():
rule = SigmaRule.from_yaml(
f"""
title: Test
id: cafedead-beef-0000-1111-0123456789ab
level: medium
status: test
date: {test_string} # possibly a yaml date
modified: '{test_string}' # always a string data type converted into date
logsource:
product: foobar
detection:
selection_1:
fieldA: valueA
condition: selection_1
"""
)
assert rule is not None
assert rule.date == expected_date, f"bad 'date' for '{test_string}'"
assert rule.modified == expected_date, f"bad 'modified' for '{test_string}'"


def test_sigmarule_datetime():
Expand Down