mirror of
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b068890fa6
Implement the "tighten rule pre-selection" algorithm described here: https://github.com/mandiant/capa/issues/2063#issuecomment-2100498720 In summary: > Rather than indexing all features from all rules, > we should pick and index the minimal set (ideally, one) of > features from each rule that must be present for the rule to match. > When we have multiple candidates, pick the feature that is > probably most uncommon and therefore "selective". This seems to work pretty well. Total evaluations when running against mimikatz drop from 19M to 1.1M (wow!) and capa seems to match around 3x more functions per second (wow wow). When doing large scale runs, capa is about 25% faster when using the vivisect backend (analysis heavy) or 3x faster when using the upcoming BinExport2 backend (minimal analysis).
883 lines
26 KiB
Python
883 lines
26 KiB
Python
# Copyright (C) 2021 Mandiant, Inc. All Rights Reserved.
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# Licensed under the Apache License, Version 2.0 (the "License");
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# you may not use this file except in compliance with the License.
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# You may obtain a copy of the License at: [package root]/LICENSE.txt
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# Unless required by applicable law or agreed to in writing, software distributed under the License
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# is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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# See the License for the specific language governing permissions and limitations under the License.
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import textwrap
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import pytest
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import capa.rules
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import capa.engine
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import capa.features.insn
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import capa.features.common
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from capa.rules import Scope
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from capa.features.common import OS, OS_ANY, OS_WINDOWS, String, MatchedRule
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def match(rules, features, va, scope=Scope.FUNCTION):
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"""
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use all matching algorithms and verify that they compute the same result.
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then, return those results to the caller so they can make their asserts.
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"""
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features1, matches1 = capa.engine.match(rules, features, va)
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ruleset = capa.rules.RuleSet(rules)
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features2, matches2 = ruleset.match(scope, features, va)
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for feature, locations in features1.items():
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assert feature in features2
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assert locations == features2[feature]
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for rulename, results in matches1.items():
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assert rulename in matches2
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assert len(results) == len(matches2[rulename])
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return features1, matches1
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def test_match_simple():
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rule = textwrap.dedent(
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"""
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rule:
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meta:
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name: test rule
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scopes:
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static: function
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dynamic: process
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namespace: testns1/testns2
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features:
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- number: 100
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"""
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)
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r = capa.rules.Rule.from_yaml(rule)
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features, matches = match([r], {capa.features.insn.Number(100): {1, 2}}, 0x0)
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assert "test rule" in matches
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assert MatchedRule("test rule") in features
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assert MatchedRule("testns1") in features
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assert MatchedRule("testns1/testns2") in features
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def test_match_range_exact():
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rule = textwrap.dedent(
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"""
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rule:
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meta:
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name: test rule
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scopes:
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static: function
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dynamic: process
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features:
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- count(number(100)): 2
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"""
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)
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r = capa.rules.Rule.from_yaml(rule)
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# just enough matches
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_, matches = match([r], {capa.features.insn.Number(100): {1, 2}}, 0x0)
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assert "test rule" in matches
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# not enough matches
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_, matches = match([r], {capa.features.insn.Number(100): {1}}, 0x0)
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assert "test rule" not in matches
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# too many matches
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_, matches = match([r], {capa.features.insn.Number(100): {1, 2, 3}}, 0x0)
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assert "test rule" not in matches
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def test_match_range_range():
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rule = textwrap.dedent(
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"""
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rule:
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meta:
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name: test rule
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scopes:
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static: function
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dynamic: process
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features:
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- count(number(100)): (2, 3)
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"""
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)
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r = capa.rules.Rule.from_yaml(rule)
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# just enough matches
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_, matches = match([r], {capa.features.insn.Number(100): {1, 2}}, 0x0)
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assert "test rule" in matches
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# enough matches
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_, matches = match([r], {capa.features.insn.Number(100): {1, 2, 3}}, 0x0)
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assert "test rule" in matches
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# not enough matches
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_, matches = match([r], {capa.features.insn.Number(100): {1}}, 0x0)
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assert "test rule" not in matches
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# too many matches
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_, matches = match([r], {capa.features.insn.Number(100): {1, 2, 3, 4}}, 0x0)
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assert "test rule" not in matches
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def test_match_range_exact_zero():
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rule = textwrap.dedent(
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"""
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rule:
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meta:
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name: test rule
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scopes:
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static: function
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dynamic: process
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features:
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- and:
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- count(number(100)): 0
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# we can't have `count(foo): 0` at the top level,
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# since we don't support top level NOT statements.
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# so we have this additional trivial feature.
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- mnemonic: mov
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"""
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)
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r = capa.rules.Rule.from_yaml(rule)
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# feature isn't indexed - good.
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_, matches = match([r], {capa.features.insn.Mnemonic("mov"): {}}, 0x0)
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assert "test rule" in matches
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# feature is indexed, but no matches.
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# i don't think we should ever really have this case, but good to check anyways.
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_, matches = match([r], {capa.features.insn.Number(100): {}, capa.features.insn.Mnemonic("mov"): {}}, 0x0)
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assert "test rule" in matches
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# too many matches
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_, matches = match([r], {capa.features.insn.Number(100): {1}, capa.features.insn.Mnemonic("mov"): {1}}, 0x0)
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assert "test rule" not in matches
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def test_match_range_with_zero():
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rule = textwrap.dedent(
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"""
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rule:
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meta:
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name: test rule
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scopes:
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static: function
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dynamic: process
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features:
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- and:
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- count(number(100)): (0, 1)
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# we can't have `count(foo): 0` at the top level,
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# since we don't support top level NOT statements.
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# so we have this additional trivial feature.
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- mnemonic: mov
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"""
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)
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r = capa.rules.Rule.from_yaml(rule)
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# ok
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_, matches = match([r], {capa.features.insn.Mnemonic("mov"): {}}, 0x0)
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assert "test rule" in matches
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_, matches = match([r], {capa.features.insn.Number(100): {}, capa.features.insn.Mnemonic("mov"): {}}, 0x0)
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assert "test rule" in matches
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_, matches = match([r], {capa.features.insn.Number(100): {1}, capa.features.insn.Mnemonic("mov"): {1}}, 0x0)
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assert "test rule" in matches
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# too many matches
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_, matches = match([r], {capa.features.insn.Number(100): {1, 2}, capa.features.insn.Mnemonic("mov"): {1, 2}}, 0x0)
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assert "test rule" not in matches
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def test_match_adds_matched_rule_feature():
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"""show that using `match` adds a feature for matched rules."""
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rule = textwrap.dedent(
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"""
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rule:
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meta:
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name: test rule
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scopes:
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static: function
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dynamic: process
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features:
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- number: 100
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"""
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)
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r = capa.rules.Rule.from_yaml(rule)
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features, _ = match([r], {capa.features.insn.Number(100): {1}}, 0x0)
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assert capa.features.common.MatchedRule("test rule") in features
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def test_match_matched_rules():
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"""show that using `match` adds a feature for matched rules."""
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rules = [
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capa.rules.Rule.from_yaml(
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textwrap.dedent(
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"""
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rule:
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meta:
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name: test rule1
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scopes:
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static: function
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dynamic: process
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features:
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- number: 100
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"""
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)
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),
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capa.rules.Rule.from_yaml(
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textwrap.dedent(
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"""
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rule:
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meta:
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name: test rule2
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scopes:
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static: function
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dynamic: process
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features:
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- match: test rule1
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"""
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)
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),
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]
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features, _ = match(
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capa.rules.topologically_order_rules(rules),
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{capa.features.insn.Number(100): {1}},
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0x0,
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)
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assert capa.features.common.MatchedRule("test rule1") in features
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assert capa.features.common.MatchedRule("test rule2") in features
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# the ordering of the rules must not matter,
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# the engine should match rules in an appropriate order.
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features, _ = match(
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capa.rules.topologically_order_rules(list(reversed(rules))),
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{capa.features.insn.Number(100): {1}},
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0x0,
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)
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assert capa.features.common.MatchedRule("test rule1") in features
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assert capa.features.common.MatchedRule("test rule2") in features
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def test_match_namespace():
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rules = [
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capa.rules.Rule.from_yaml(
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textwrap.dedent(
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"""
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rule:
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meta:
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name: CreateFile API
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scopes:
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static: function
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dynamic: process
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namespace: file/create/CreateFile
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features:
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- api: CreateFile
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"""
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)
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),
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capa.rules.Rule.from_yaml(
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textwrap.dedent(
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"""
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rule:
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meta:
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name: WriteFile API
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scopes:
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static: function
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dynamic: process
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namespace: file/write
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features:
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- api: WriteFile
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"""
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)
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),
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capa.rules.Rule.from_yaml(
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textwrap.dedent(
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"""
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rule:
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meta:
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name: file-create
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scopes:
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static: function
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dynamic: process
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features:
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- match: file/create
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"""
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)
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),
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capa.rules.Rule.from_yaml(
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textwrap.dedent(
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"""
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rule:
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meta:
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name: filesystem-any
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scopes:
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static: function
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dynamic: process
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features:
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- match: file
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"""
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)
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),
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]
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features, matches = match(
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capa.rules.topologically_order_rules(rules),
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{capa.features.insn.API("CreateFile"): {1}},
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0x0,
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)
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assert "CreateFile API" in matches
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assert "file-create" in matches
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assert "filesystem-any" in matches
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assert capa.features.common.MatchedRule("file") in features
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assert capa.features.common.MatchedRule("file/create") in features
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assert capa.features.common.MatchedRule("file/create/CreateFile") in features
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features, matches = match(
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capa.rules.topologically_order_rules(rules),
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{capa.features.insn.API("WriteFile"): {1}},
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0x0,
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)
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assert "WriteFile API" in matches
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assert "file-create" not in matches
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assert "filesystem-any" in matches
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def test_match_substring():
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rules = [
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capa.rules.Rule.from_yaml(
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textwrap.dedent(
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"""
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rule:
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meta:
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name: test rule
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scopes:
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static: function
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dynamic: process
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features:
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- and:
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- substring: abc
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"""
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)
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),
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]
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features, _ = match(
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capa.rules.topologically_order_rules(rules),
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{capa.features.common.String("aaaa"): {1}},
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0x0,
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)
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assert capa.features.common.MatchedRule("test rule") not in features
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features, _ = match(
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capa.rules.topologically_order_rules(rules),
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{capa.features.common.String("abc"): {1}},
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0x0,
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)
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assert capa.features.common.MatchedRule("test rule") in features
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features, _ = match(
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capa.rules.topologically_order_rules(rules),
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{capa.features.common.String("111abc222"): {1}},
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0x0,
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)
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assert capa.features.common.MatchedRule("test rule") in features
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features, _ = match(
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capa.rules.topologically_order_rules(rules),
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{capa.features.common.String("111abc"): {1}},
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0x0,
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)
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assert capa.features.common.MatchedRule("test rule") in features
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features, _ = match(
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capa.rules.topologically_order_rules(rules),
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{capa.features.common.String("abc222"): {1}},
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0x0,
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)
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assert capa.features.common.MatchedRule("test rule") in features
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def test_match_regex():
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rules = [
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capa.rules.Rule.from_yaml(
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textwrap.dedent(
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"""
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rule:
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meta:
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name: test rule
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scopes:
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static: function
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dynamic: process
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features:
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- and:
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- string: /.*bbbb.*/
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"""
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)
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),
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capa.rules.Rule.from_yaml(
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textwrap.dedent(
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"""
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rule:
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meta:
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name: rule with implied wildcards
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scopes:
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static: function
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dynamic: process
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features:
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- and:
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- string: /bbbb/
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"""
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)
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),
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capa.rules.Rule.from_yaml(
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textwrap.dedent(
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"""
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rule:
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meta:
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name: rule with anchor
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scopes:
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static: function
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dynamic: process
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features:
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- and:
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- string: /^bbbb/
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"""
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)
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),
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]
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features, _ = match(
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capa.rules.topologically_order_rules(rules),
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{capa.features.insn.Number(100): {1}},
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0x0,
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)
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assert capa.features.common.MatchedRule("test rule") not in features
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features, _ = match(
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capa.rules.topologically_order_rules(rules),
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{capa.features.common.String("aaaa"): {1}},
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0x0,
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)
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assert capa.features.common.MatchedRule("test rule") not in features
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features, _ = match(
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capa.rules.topologically_order_rules(rules),
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{capa.features.common.String("aBBBBa"): {1}},
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0x0,
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)
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assert capa.features.common.MatchedRule("test rule") not in features
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features, _ = match(
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capa.rules.topologically_order_rules(rules),
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{capa.features.common.String("abbbba"): {1}},
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0x0,
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)
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assert capa.features.common.MatchedRule("test rule") in features
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assert capa.features.common.MatchedRule("rule with implied wildcards") in features
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assert capa.features.common.MatchedRule("rule with anchor") not in features
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def test_match_regex_ignorecase():
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rules = [
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capa.rules.Rule.from_yaml(
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textwrap.dedent(
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"""
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rule:
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meta:
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name: test rule
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scopes:
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static: function
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dynamic: process
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features:
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- and:
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- string: /.*bbbb.*/i
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"""
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)
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),
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]
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features, _ = match(
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capa.rules.topologically_order_rules(rules),
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{capa.features.common.String("aBBBBa"): {1}},
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0x0,
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)
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assert capa.features.common.MatchedRule("test rule") in features
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def test_match_regex_complex():
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rules = [
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capa.rules.Rule.from_yaml(
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textwrap.dedent(
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r"""
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rule:
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meta:
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name: test rule
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scopes:
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static: function
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dynamic: process
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features:
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- or:
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- string: /.*HARDWARE\\Key\\key with spaces\\.*/i
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"""
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)
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),
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]
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features, _ = match(
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capa.rules.topologically_order_rules(rules),
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{capa.features.common.String(r"Hardware\Key\key with spaces\some value"): {1}},
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0x0,
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)
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assert capa.features.common.MatchedRule("test rule") in features
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def test_match_regex_values_always_string():
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rules = [
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capa.rules.Rule.from_yaml(
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textwrap.dedent(
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"""
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rule:
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meta:
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name: test rule
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scopes:
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static: function
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dynamic: process
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features:
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- or:
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- string: /123/
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- string: /0x123/
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"""
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)
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),
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]
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features, _ = match(
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capa.rules.topologically_order_rules(rules),
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{capa.features.common.String("123"): {1}},
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0x0,
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)
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assert capa.features.common.MatchedRule("test rule") in features
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features, _ = match(
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capa.rules.topologically_order_rules(rules),
|
|
{capa.features.common.String("0x123"): {1}},
|
|
0x0,
|
|
)
|
|
assert capa.features.common.MatchedRule("test rule") in features
|
|
|
|
|
|
@pytest.mark.xfail(reason="can't have top level NOT")
|
|
def test_match_only_not():
|
|
rule = textwrap.dedent(
|
|
"""
|
|
rule:
|
|
meta:
|
|
name: test rule
|
|
scopes:
|
|
static: function
|
|
dynamic: process
|
|
namespace: testns1/testns2
|
|
features:
|
|
- not:
|
|
- number: 99
|
|
"""
|
|
)
|
|
r = capa.rules.Rule.from_yaml(rule)
|
|
|
|
_, matches = match([r], {capa.features.insn.Number(100): {1, 2}}, 0x0)
|
|
assert "test rule" in matches
|
|
|
|
|
|
def test_match_not():
|
|
rule = textwrap.dedent(
|
|
"""
|
|
rule:
|
|
meta:
|
|
name: test rule
|
|
scopes:
|
|
static: function
|
|
dynamic: process
|
|
namespace: testns1/testns2
|
|
features:
|
|
- and:
|
|
- mnemonic: mov
|
|
- not:
|
|
- number: 99
|
|
"""
|
|
)
|
|
r = capa.rules.Rule.from_yaml(rule)
|
|
|
|
_, matches = match([r], {capa.features.insn.Number(100): {1, 2}, capa.features.insn.Mnemonic("mov"): {1, 2}}, 0x0)
|
|
assert "test rule" in matches
|
|
|
|
|
|
@pytest.mark.xfail(reason="can't have nested NOT")
|
|
def test_match_not_not():
|
|
rule = textwrap.dedent(
|
|
"""
|
|
rule:
|
|
meta:
|
|
name: test rule
|
|
scopes:
|
|
static: function
|
|
dynamic: process
|
|
namespace: testns1/testns2
|
|
features:
|
|
- not:
|
|
- not:
|
|
- number: 100
|
|
"""
|
|
)
|
|
r = capa.rules.Rule.from_yaml(rule)
|
|
|
|
_, matches = match([r], {capa.features.insn.Number(100): {1, 2}}, 0x0)
|
|
assert "test rule" in matches
|
|
|
|
|
|
def test_match_operand_number():
|
|
rule = textwrap.dedent(
|
|
"""
|
|
rule:
|
|
meta:
|
|
name: test rule
|
|
scopes:
|
|
static: function
|
|
dynamic: process
|
|
features:
|
|
- and:
|
|
- operand[0].number: 0x10
|
|
"""
|
|
)
|
|
r = capa.rules.Rule.from_yaml(rule)
|
|
|
|
assert capa.features.insn.OperandNumber(0, 0x10) in {capa.features.insn.OperandNumber(0, 0x10)}
|
|
|
|
_, matches = match([r], {capa.features.insn.OperandNumber(0, 0x10): {1, 2}}, 0x0)
|
|
assert "test rule" in matches
|
|
|
|
# mismatching index
|
|
_, matches = match([r], {capa.features.insn.OperandNumber(1, 0x10): {1, 2}}, 0x0)
|
|
assert "test rule" not in matches
|
|
|
|
# mismatching value
|
|
_, matches = match([r], {capa.features.insn.OperandNumber(0, 0x11): {1, 2}}, 0x0)
|
|
assert "test rule" not in matches
|
|
|
|
|
|
def test_match_operand_offset():
|
|
rule = textwrap.dedent(
|
|
"""
|
|
rule:
|
|
meta:
|
|
name: test rule
|
|
scopes:
|
|
static: function
|
|
dynamic: process
|
|
features:
|
|
- and:
|
|
- operand[0].offset: 0x10
|
|
"""
|
|
)
|
|
r = capa.rules.Rule.from_yaml(rule)
|
|
|
|
assert capa.features.insn.OperandOffset(0, 0x10) in {capa.features.insn.OperandOffset(0, 0x10)}
|
|
|
|
_, matches = match([r], {capa.features.insn.OperandOffset(0, 0x10): {1, 2}}, 0x0)
|
|
assert "test rule" in matches
|
|
|
|
# mismatching index
|
|
_, matches = match([r], {capa.features.insn.OperandOffset(1, 0x10): {1, 2}}, 0x0)
|
|
assert "test rule" not in matches
|
|
|
|
# mismatching value
|
|
_, matches = match([r], {capa.features.insn.OperandOffset(0, 0x11): {1, 2}}, 0x0)
|
|
assert "test rule" not in matches
|
|
|
|
|
|
def test_match_property_access():
|
|
rule = textwrap.dedent(
|
|
"""
|
|
rule:
|
|
meta:
|
|
name: test rule
|
|
scopes:
|
|
static: function
|
|
dynamic: process
|
|
features:
|
|
- and:
|
|
- property/read: System.IO.FileInfo::Length
|
|
"""
|
|
)
|
|
r = capa.rules.Rule.from_yaml(rule)
|
|
|
|
assert capa.features.insn.Property("System.IO.FileInfo::Length", capa.features.common.FeatureAccess.READ) in {
|
|
capa.features.insn.Property("System.IO.FileInfo::Length", capa.features.common.FeatureAccess.READ)
|
|
}
|
|
|
|
_, matches = match(
|
|
[r],
|
|
{capa.features.insn.Property("System.IO.FileInfo::Length", capa.features.common.FeatureAccess.READ): {1, 2}},
|
|
0x0,
|
|
)
|
|
assert "test rule" in matches
|
|
|
|
# mismatching access
|
|
_, matches = match(
|
|
[r],
|
|
{capa.features.insn.Property("System.IO.FileInfo::Length", capa.features.common.FeatureAccess.WRITE): {1, 2}},
|
|
0x0,
|
|
)
|
|
assert "test rule" not in matches
|
|
|
|
# mismatching value
|
|
_, matches = match(
|
|
[r],
|
|
{capa.features.insn.Property("System.IO.FileInfo::Size", capa.features.common.FeatureAccess.READ): {1, 2}},
|
|
0x0,
|
|
)
|
|
assert "test rule" not in matches
|
|
|
|
|
|
def test_match_os_any():
|
|
rule = textwrap.dedent(
|
|
"""
|
|
rule:
|
|
meta:
|
|
name: test rule
|
|
scopes:
|
|
static: function
|
|
dynamic: process
|
|
features:
|
|
- or:
|
|
- and:
|
|
- or:
|
|
- os: windows
|
|
- os: linux
|
|
- os: macos
|
|
- string: "Hello world"
|
|
- and:
|
|
- os: any
|
|
- string: "Goodbye world"
|
|
"""
|
|
)
|
|
r = capa.rules.Rule.from_yaml(rule)
|
|
|
|
_, matches = match(
|
|
[r],
|
|
{OS(OS_ANY): {1}, String("Hello world"): {1}},
|
|
0x0,
|
|
)
|
|
assert "test rule" in matches
|
|
|
|
_, matches = match(
|
|
[r],
|
|
{OS(OS_WINDOWS): {1}, String("Hello world"): {1}},
|
|
0x0,
|
|
)
|
|
assert "test rule" in matches
|
|
|
|
_, matches = match(
|
|
[r],
|
|
{OS(OS_ANY): {1}, String("Goodbye world"): {1}},
|
|
0x0,
|
|
)
|
|
assert "test rule" in matches
|
|
|
|
_, matches = match(
|
|
[r],
|
|
{OS(OS_WINDOWS): {1}, String("Goodbye world"): {1}},
|
|
0x0,
|
|
)
|
|
assert "test rule" in matches
|
|
|
|
|
|
# this test demonstrates the behavior of unstable features that may change before the next major release.
|
|
def test_index_features_and_unstable():
|
|
rule = textwrap.dedent(
|
|
"""
|
|
rule:
|
|
meta:
|
|
name: test rule
|
|
scopes:
|
|
static: function
|
|
dynamic: process
|
|
features:
|
|
- and:
|
|
- mnemonic: mov
|
|
- api: CreateFileW
|
|
"""
|
|
)
|
|
r = capa.rules.Rule.from_yaml(rule)
|
|
rr = capa.rules.RuleSet([r])
|
|
index: capa.rules.RuleSet._RuleFeatureIndex = rr._feature_indexes_by_scopes[capa.rules.Scope.FUNCTION]
|
|
|
|
# there's a single rule, and its indexed by a single feature
|
|
assert len(index.rules_by_feature) == 1
|
|
# and we index by the more uncommon API feature, not the common mnemonic feature
|
|
assert capa.features.insn.API("CreateFileW") in index.rules_by_feature
|
|
|
|
assert not index.string_rules
|
|
assert not index.bytes_rules
|
|
|
|
|
|
# this test demonstrates the behavior of unstable features that may change before the next major release.
|
|
def test_index_features_or_unstable():
|
|
rule = textwrap.dedent(
|
|
"""
|
|
rule:
|
|
meta:
|
|
name: test rule
|
|
scopes:
|
|
static: function
|
|
dynamic: process
|
|
features:
|
|
- or:
|
|
- mnemonic: mov
|
|
- api: CreateFileW
|
|
"""
|
|
)
|
|
r = capa.rules.Rule.from_yaml(rule)
|
|
rr = capa.rules.RuleSet([r])
|
|
index: capa.rules.RuleSet._RuleFeatureIndex = rr._feature_indexes_by_scopes[capa.rules.Scope.FUNCTION]
|
|
|
|
# there's a single rule, and its indexed by both features,
|
|
# because they fall under the single root OR node.
|
|
assert len(index.rules_by_feature) == 2
|
|
assert capa.features.insn.API("CreateFileW") in index.rules_by_feature
|
|
assert capa.features.insn.Mnemonic("mov") in index.rules_by_feature
|
|
|
|
assert not index.string_rules
|
|
assert not index.bytes_rules
|
|
|
|
|
|
# this test demonstrates the behavior of unstable features that may change before the next major release.
|
|
def test_index_features_nested_unstable():
|
|
rule = textwrap.dedent(
|
|
"""
|
|
rule:
|
|
meta:
|
|
name: test rule
|
|
scopes:
|
|
static: function
|
|
dynamic: process
|
|
features:
|
|
- and:
|
|
- mnemonic: mov
|
|
- or:
|
|
- api: CreateFileW
|
|
- string: foo
|
|
"""
|
|
)
|
|
r = capa.rules.Rule.from_yaml(rule)
|
|
rr = capa.rules.RuleSet([r])
|
|
index: capa.rules.RuleSet._RuleFeatureIndex = rr._feature_indexes_by_scopes[capa.rules.Scope.FUNCTION]
|
|
|
|
# there's a single rule, and its indexed by the two uncommon features,
|
|
# not the single common feature.
|
|
assert len(index.rules_by_feature) == 2
|
|
assert capa.features.insn.API("CreateFileW") in index.rules_by_feature
|
|
assert capa.features.common.String("foo") in index.rules_by_feature
|
|
assert capa.features.insn.Mnemonic("mov") not in index.rules_by_feature
|
|
|
|
assert not index.string_rules
|
|
assert not index.bytes_rules
|