# This file is Copyright 2019 Volatility Foundation and licensed under the Volatility Software License 1.0
# which is available at https://www.volatilityfoundation.org/license/vsl-v1.0
#
import logging
from typing import Any, Dict, Iterable, List, Tuple
from volatility3.framework import interfaces, renderers
from volatility3.framework.configuration import requirements
from volatility3.framework.interfaces import plugins
from volatility3.framework.layers import resources
from volatility3.framework.renderers import format_hints
vollog = logging.getLogger(__name__)
USE_YARA_X = False
try:
import yara_x
USE_YARA_X = True
except ImportError:
try:
import yara
if tuple(int(x) for x in yara.__version__.split(".")) < (3, 8):
raise ImportError
vollog.debug("Using yara-python module")
except ImportError:
vollog.info(
"Neither yara-x nor yara-python (>3.8.0) module not found, plugin (and dependent plugins) not available"
)
raise
[docs]class YaraScanner(interfaces.layers.ScannerInterface):
_version = (2, 1, 0)
# yara.Rules isn't exposed, so we can't type this properly
def __init__(self, rules) -> None:
super().__init__()
if rules is None:
raise ValueError("No rules provided to YaraScanner")
self._rules = rules
self.st_object = (
None
if USE_YARA_X
else not tuple(int(x) for x in yara.__version__.split(".")) < (4, 3)
)
def __call__(
self, data: bytes, data_offset: int
) -> Iterable[Tuple[int, str, str, bytes]]:
if USE_YARA_X:
for match in self._rules.scan(data).matching_rules:
for match_string in match.patterns:
for instance in match_string.matches:
yield (
instance.offset + data_offset,
f"{match.namespace}.{match.identifier}",
match_string.identifier,
data[instance.offset : instance.offset + instance.length],
)
else:
for match in self._rules.match(data=data):
if YaraScan.yara_returns_instances():
for match_string in match.strings:
for instance in match_string.instances:
yield (
instance.offset + data_offset,
match.rule,
match_string.identifier,
instance.matched_data,
)
else:
for offset, name, value in match.strings:
yield (offset + data_offset, match.rule, name, value)
[docs] @staticmethod
def get_rule(rule):
if USE_YARA_X:
return yara_x.compile(f"rule r1 {{strings: $a = {rule} condition: $a}}")
return yara.compile(
sources={"n": f"rule r1 {{strings: $a = {rule} condition: $a}}"}
)
[docs] @staticmethod
def from_compiled_file(filepath):
with resources.ResourceAccessor().open(filepath, "rb") as fp:
if USE_YARA_X:
return yara_x.Rules.deserialize_from(file=fp)
return yara.load(file=fp)
[docs] @staticmethod
def from_file(filepath):
with resources.ResourceAccessor().open(filepath, "rb") as fp:
if USE_YARA_X:
return yara_x.compile(fp.read().decode())
return yara.compile(file=fp)
[docs]class YaraScan(plugins.PluginInterface):
"""Scans kernel memory using yara rules (string or file)."""
_required_framework_version = (2, 0, 0)
_version = (2, 0, 0)
_yara_x = USE_YARA_X
[docs] @classmethod
def get_requirements(cls) -> List[interfaces.configuration.RequirementInterface]:
"""Returns the requirements needed to run yarascan directly, combining the TranslationLayerRequirement
and the requirements from get_yarascan_option_requirements."""
return cls.get_yarascan_option_requirements() + [
requirements.TranslationLayerRequirement(
name="primary",
description="Memory layer for the kernel",
architectures=["Intel32", "Intel64"],
)
]
[docs] @classmethod
def get_yarascan_option_requirements(
cls,
) -> List[interfaces.configuration.RequirementInterface]:
"""Returns the requirements needed for the command lines options used by yarascan. This can
then also be used by other plugins that are using yarascan. This does not include a
TranslationLayerRequirement or a ModuleRequirement."""
return [
requirements.BooleanRequirement(
name="insensitive",
description="Makes the search case insensitive",
default=False,
optional=True,
),
requirements.BooleanRequirement(
name="wide",
description="Match wide (unicode) strings",
default=False,
optional=True,
),
requirements.StringRequirement(
name="yara_string",
description="Yara rules (as a string)",
optional=True,
),
requirements.URIRequirement(
name="yara_file",
description="Yara rules (as a file)",
optional=True,
),
# This additional requirement is to follow suit with upstream, who feel that compiled rules could potentially be used to execute malicious code
# As such, there's a separate option to run compiled files, as happened with yara-3.9 and later
requirements.URIRequirement(
name="yara_compiled_file",
description="Yara compiled rules (as a file)",
optional=True,
),
requirements.IntRequirement(
name="max_size",
default=0x40000000,
description="Set the maximum size (default is 1GB)",
optional=True,
),
]
[docs] @classmethod
def yara_returns_instances(cls) -> bool:
return not tuple(int(x) for x in yara.__version__.split(".")) < (4, 3)
[docs] @classmethod
def process_yara_options(cls, config: Dict[str, Any]):
rules = None
if config.get("yara_string") is not None:
rule = config["yara_string"]
if rule[0] not in ["{", "/"]:
rule = f'"{rule}"'
if config.get("case", False):
rule += " nocase"
if config.get("wide", False):
rule += " wide ascii"
rules = YaraScanner.get_rule(rule)
elif config.get("yara_file") is not None:
vollog.debug(f"Plain file: {config['yara_file']} - yara-x: {USE_YARA_X}")
rules = YaraScanner.from_file(config["yara_file"])
elif config.get("yara_compiled_file") is not None:
vollog.debug(
f"Compiled file: {config['yara_compiled_file']} - yara-x: {USE_YARA_X}"
)
rules = YaraScanner.from_compiled_file(config["yara_compiled_file"])
else:
vollog.error("No yara rules, nor yara rules file were specified")
return rules
def _generator(self):
rules = self.process_yara_options(dict(self.config))
layer = self.context.layers[self.config["primary"]]
for offset, rule_name, name, value in layer.scan(
context=self.context, scanner=YaraScanner(rules=rules)
):
yield 0, (format_hints.Hex(offset), rule_name, name, value)
[docs] def run(self):
return renderers.TreeGrid(
[
("Offset", format_hints.Hex),
("Rule", str),
("Component", str),
("Value", bytes),
],
self._generator(),
)