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FEAT(capa2sarif) Add SARIF conversion script from json output (#2093)
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* feat(capa2sarif): add new sarif conversion script converting json output to sarif schema, update dependencies, and update changelog

* fix(capa2sarif): removing copy and paste transcription errors

* fix(capa2sarif): remove dependencies from pyproject toml to guarded import statements

* chore(capa2sarif): adding node in readme specifying dependency and applied auto formatter for styling

* style(capa2sarif): applied import sorting and fixed typo in invocations function

* test(capa2sarif): adding simple test for capa to sarif conversion script using existing result document

* style(capa2sarif): fixing typo in version string in usage

* style(capa2sarif): isort failing due to reordering of typehint imports

* style(capa2sarif): fixing import order as isort on local machine was not updating code

---------

Co-authored-by: ReversingWithMe <ryanv@rewith.me>
Co-authored-by: Willi Ballenthin <wballenthin@google.com>
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@ReversingWithMe @williballenthin
3 people committed Jun 11, 2024
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1 change: 1 addition & 0 deletions CHANGELOG.md
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Expand Up @@ -7,6 +7,7 @@

- add function in capa/helpers to load plain and compressed JSON reports #1883 @Rohit1123
- document Antivirus warnings and VirusTotal false positive detections #2028 @RionEV @mr-tz
- Add json to sarif conversion script @reversingwithme
- render maec/* fields #843 @s-ff
- replace Halo spinner with Rich #2086 @s-ff
- optimize rule matching #2080 @williballenthin
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375 changes: 375 additions & 0 deletions scripts/capa2sarif.py
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# Copyright (C) 2021 Mandiant, Inc. All Rights Reserved.
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at: [package root]/LICENSE.txt
# Unless required by applicable law or agreed to in writing, software distributed under the License
# is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and limitations under the License.
"""
Convert capa json output to sarif schema
usage: capa2sarif.py [-h] [-g] [-r] [-t TAG] [--version] capa_output
Capa to SARIF analysis file
positional arguments:
capa_output Path to capa JSON output file
optional arguments:
-h, --help show this help message and exit
--version show program's version number and exit
-t TAG, --tag TAG filter on rule meta field values (ruleid)
Requires:
- sarif_om 1.0.4
- jschema_to_python 1.2.3
"""
import sys
import json
import logging
import argparse
from typing import List, Optional
from pathlib import Path

from capa.version import __version__

logger = logging.getLogger("capa2sarif")

# Dependencies
try:
from sarif_om import Run, Tool, SarifLog, ToolComponent
except ImportError as e:
logger.error(
"Required import `sarif_om` is not installed. This is solved by installing `python3 -m pip install sarif_om>=1.0.4`. %s",
e,
)
exit(-4)

try:
from jschema_to_python.to_json import to_json
except ImportError as e:
logger.error(
"Required import `jschema_to_python` is not installed. This is solved by installing `python3 -m pip install jschema_to_python>=1.2.3`, %s",
e,
)
exit(-4)


def _parse_args() -> argparse.Namespace:
parser = argparse.ArgumentParser(description="Capa to SARIF analysis file")

# Positional argument
parser.add_argument("capa_output", help="Path to capa JSON output file")

# Optional arguments
parser.add_argument(
"-g",
"--ghidra-compat",
action="store_true",
help="Compatibility for Ghidra 11.0.X",
)
parser.add_argument(
"-r",
"--radare-compat",
action="store_true",
help="Compatibility for Radare r2sarif plugin v2.0",
)
parser.add_argument("-t", "--tag", help="Filter on rule meta field values (ruleid)")
parser.add_argument(
"--version", action="version", version=f"%(prog)s {__version__}"
)

return parser.parse_args()


def main() -> int:
logging.basicConfig(level=logging.INFO)
logging.getLogger().setLevel(logging.INFO)

args = _parse_args()

try:
with Path(args.capa_output).open() as capa_output:
json_data = json.load(capa_output)
except ValueError:
logger.error(
"Input data was not valid JSON, input should be a capa json output file."
)
return -1
except json.JSONDecodeError:
# An exception has occured
logger.error(
"Input data was not valid JSON, input should be a capa json output file."
)
return -2

# Marshall json into Sarif
# Create baseline sarif structure to be populated from json data
sarif_structure: Optional[dict] = _sarif_boilerplate(
json_data["meta"], json_data["rules"]
)
if sarif_structure is None:
logger.errort("An Error has occured creating default sarif structure.")
return -3

_populate_artifact(sarif_structure, json_data["meta"])
_populate_invocations(sarif_structure, json_data["meta"])
_populate_results(sarif_structure, json_data["rules"], args.ghidra_compat)

if args.ghidra_compat:
# Ghidra can't handle this structure as of 11.0.x
if "invocations" in sarif_structure["runs"][0]:
del sarif_structure["runs"][0]["invocations"]

# artifacts must include a description as well with a text field.
if "artifacts" in sarif_structure["runs"][0]:
sarif_structure["runs"][0]["artifacts"][0]["description"] = {
"text": "placeholder"
}

# For better compliance with Ghidra table. Iteraction through properties['additionalProperties']
"""
"additionalProperties": {
"to": "<hex addr>",
"offset": 0,
"primary": true,
"index": <>"",
"kind": "<kind column value>",
"opIndex": 0,
"sourceType": ""
}
"""

if args.radare_compat:
# Add just enough for passing tests
_add_filler_optional(json_data, sarif_structure)

print(json.dumps(sarif_structure, indent=4)) # noqa: T201
return 0


def _sarif_boilerplate(data_meta: dict, data_rules: dict) -> Optional[dict]:
# Only track rules that appear in this log, not full 1k
rules = []
# Parse rules from parsed sarif structure
for key in data_rules:
# Use attack as default, if both exist then only use attack, if neither exist use the name of rule for ruleID
# this is not good practice to use long name for ruleID
attack_length = len(data_rules[key]["meta"]["attack"])
mbc_length = len(data_rules[key]["meta"]["mbc"])
if attack_length or mbc_length:
id = (
data_rules[key]["meta"]["attack"][0]["id"]
if attack_length > 0
else data_rules[key]["meta"]["mbc"][0]["id"]
)
else:
id = data_rules[key]["meta"]["name"]

# Append current rule
rules.append(
{
# Default to attack identifier, fall back to MBC, mainly relevant if both are present
"id": id,
"name": data_rules[key]["meta"]["name"],
"shortDescription": {"text": data_rules[key]["meta"]["name"]},
"messageStrings": {
"default": {"text": data_rules[key]["meta"]["name"]}
},
"properties": {
"namespace": data_rules[key]["meta"]["namespace"]
if "namespace" in data_rules[key]["meta"]
else [],
"scopes": data_rules[key]["meta"]["scopes"],
"references": data_rules[key]["meta"]["references"],
"lib": data_rules[key]["meta"]["lib"],
},
}
)

tool = Tool(
driver=ToolComponent(
name="Capa",
version=__version__,
information_uri="https://github.com/mandiant/capa",
rules=rules,
)
)

# Create a SARIF Log object, populate with a single run
sarif_log = SarifLog(
version="2.1.0",
schema_uri="https://docs.oasis-open.org/sarif/sarif/v2.1.0/cos02/schemas/sarif-schema-2.1.0.json",
runs=[Run(tool=tool, results=[], artifacts=[], invocations=[])],
)

# Convert the SARIF log to a dictionary and then to a JSON string
try:
sarif_outline = json.loads(to_json(sarif_log))
except json.JSONDecodeError:
# An exception has occured
return None

return sarif_outline


def _populate_artifact(sarif_log: dict, meta_data: dict) -> None:
"""
@param sarif_log: dict - sarif data structure including runs
@param meta_data: dict - Capa meta output
@returns None, updates sarif_log via side-effects
"""
sample = meta_data["sample"]
artifact = {
"location": {"uri": sample["path"]},
"roles": ["analysisTarget"],
"hashes": {
"md5": sample["md5"],
"sha-1": sample["sha1"],
"sha-256": sample["sha256"],
},
}
sarif_log["runs"][0]["artifacts"].append(artifact)


def _populate_invocations(sarif_log: dict, meta_data: dict) -> None:
"""
@param sarif_log: dict - sarif data structure including runs
@param meta_data: dict - Capa meta output
@returns None, updates sarif_log via side-effects
"""
analysis_time = meta_data["timestamp"]
argv = meta_data["argv"]
analysis = meta_data["analysis"]
invoke = {
"commandLine": "capa " + " ".join(argv),
"arguments": argv if len(argv) > 0 else [],
# Format in Zulu time, this may require a conversion from local timezone
"endTimeUtc": f"{analysis_time}Z",
"executionSuccessful": True,
"properties": {
"format": analysis["format"],
"arch": analysis["arch"],
"os": analysis["os"],
"extractor": analysis["extractor"],
"rule_location": analysis["rules"],
"base_address": analysis["base_address"],
},
}
sarif_log["runs"][0]["invocations"].append(invoke)


def _enumerate_evidence(node: dict, related_count: int) -> List[dict]:
related_locations = []
if node.get("success") and node.get("node").get("type") != "statement":
label = ""
if node.get("node").get("type") == "feature":
if node.get("node").get("feature").get("type") == "api":
label = "api: " + node.get("node").get("feature").get("api")
elif node.get("node").get("feature").get("type") == "match":
label = "match: " + node.get("node").get("feature").get("match")
elif node.get("node").get("feature").get("type") == "number":
label = f"number: {node.get('node').get('feature').get('description')} ({node.get('node').get('feature').get('number')})"
elif node.get("node").get("feature").get("type") == "offset":
label = f"offset: {node.get('node').get('feature').get('description')} ({node.get('node').get('feature').get('offset')})"
elif node.get("node").get("feature").get("type") == "mnemonic":
label = f"mnemonic: {node.get('node').get('feature').get('mnemonic')}"
elif node.get("node").get("feature").get("type") == "characteristic":
label = f"characteristic: {node.get('node').get('feature').get('characteristic')}"
elif node.get("node").get("feature").get("type") == "os":
label = f"os: {node.get('node').get('feature').get('os')}"
elif node.get("node").get("feature").get("type") == "operand number":
label = f"operand: ({node.get('node').get('feature').get('index')} ) {node.get('node').get('feature').get('description')} ({node.get('node').get('feature').get('operand_number')})"
else:
logger.error(
"Not implemented %s",
node.get("node").get("feature").get("type"),
file=sys.stderr,
)
return []
else:
logger.error(
"Not implemented %s", node.get("node").get("type"), file=sys.stderr
)
return []

for loc in node.get("locations"):
if loc["type"] != "absolute":
continue

related_locations.append(
{
"id": related_count,
"message": {"text": label},
"physicalLocation": {"address": {"absoluteAddress": loc["value"]}},
}
)
related_count += 1

if node.get("success") and node.get("node").get("type") == "statement":
for child in node.get("children"):
related_locations += _enumerate_evidence(child, related_count)

return related_locations


def _populate_results(sarif_log: dict, data_rules: dict, ghidra_compat: bool) -> None:
"""
@param sarif_log: dict - sarif data structure including runs
@param meta_data: dict - Capa meta output
@returns None, updates sarif_log via side-effects
"""
results = sarif_log["runs"][0]["results"]

# Parse rules from parsed sarif structure
for key in data_rules:
# Use attack as default, if both exist then only use attack, if neither exist use the name of rule for ruleID
# this is not good practice to use long name for ruleID.
attack_length = len(data_rules[key]["meta"]["attack"])
mbc_length = len(data_rules[key]["meta"]["mbc"])
if attack_length or mbc_length:
id = (
data_rules[key]["meta"]["attack"][0]["id"]
if attack_length > 0
else data_rules[key]["meta"]["mbc"][0]["id"]
)
else:
id = data_rules[key]["meta"]["name"]

for address, details in data_rules[key]["matches"]:
related_cnt = 0
related_locations = _enumerate_evidence(details, related_cnt)

res = {
"ruleId": id,
"level": "none" if not ghidra_compat else "NONE",
"message": {"text": data_rules[key]["meta"]["name"]},
"kind": "informational" if not ghidra_compat else "INFORMATIONAL",
"locations": [
{
"physicalLocation": {
"address": {
"absoluteAddress": address["value"],
}
},
}
],
}
if not ghidra_compat:
res["relatedLocations"] = related_locations

results.append(res)


def _add_filler_optional(capa_result: dict, sarif_log: dict) -> None:
"""Update sarif file with just enough fields to pass radare tests"""
base_address = capa_result["meta"]["analysis"]["base_address"]["value"]
# Assume there is only one run, and one binary artifact
artifact = sarif_log["runs"][0]["artifacts"][0]
if "properties" not in artifact:
artifact["properties"] = {}
if "additionalProperties" not in artifact["properties"]:
artifact["properties"]["additionalProperties"] = {}
if "imageBase" not in artifact["properties"]["additionalProperties"]:
artifact["properties"]["additionalProperties"]["imageBase"] = base_address


if __name__ == "__main__":
sys.exit(main())
1 change: 1 addition & 0 deletions tests/test_scripts.py
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Expand Up @@ -40,6 +40,7 @@ def get_rule_path():
[
pytest.param("capa2yara.py", [get_rules_path()]),
pytest.param("capafmt.py", [get_rule_path()]),
pytest.param("capa2sarif.py", [Path(__file__).resolve().parent / "data" / "rd" / "Practical Malware Analysis Lab 01-01.dll_.json"]),
# testing some variations of linter script
pytest.param("lint.py", ["-t", "create directory", get_rules_path()]),
# `create directory` rule has native and .NET example PEs
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