capa/scripts/show-features.py

#!/usr/bin/env python2
"""
Copyright (C) 2020 FireEye, 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.

show-features

Show the features that capa extracts from the given sample,
to assist with the development of rules.

If you have a function with a capability that you'd like to detect,
you can run this tool and grep for the function/basic block/instruction addresses
to see what capa picks up.
This way, you can verify that capa successfully notices the features you'd reference.

Example::

    $ python scripts/show-features.py /tmp/suspicious.dll_
    ...
    file: 0x10004e4d: export(__entry)
    file: 0x10004706: export(Install)
    file: 0x10004c2b: export(uninstallA)
    file: 0x10005034: import(kernel32.GetStartupInfoA)
    file: 0x10005034: import(GetStartupInfoA)
    file: 0x10005048: import(kernel32.SetLastError)
    file: 0x00004e10: string(Y29ubmVjdA==)
    file: 0x00004e28: string(practicalmalwareanalysis.com)
    file: 0x00004e68: string(serve.html)
    file: 0x00004eb8: string(dW5zdXBwb3J0)
    file: 0x00004ec8: string(c2xlZXA=)
    func: 0x100012c2: characteristic(calls to)
    func: 0x10001000: characteristic(loop)
    bb  : 0x10001000: basic block
    insn: 0x10001000: mnemonic(push)
    insn: 0x10001001: mnemonic(push)
    insn: 0x10001002: mnemonic(push)
    insn: 0x10001003: mnemonic(push)
    insn: 0x10001004: mnemonic(push)
    insn: 0x10001005: mnemonic(push)
    insn: 0x10001006: mnemonic(xor)
    insn: 0x10001008: number(0x1)
    insn: 0x10001008: mnemonic(mov)
    bb  : 0x1000100a: basic block
    bb  : 0x1000100a: characteristic(tight loop)
    insn: 0x1000100a: mnemonic(movzx)
    insn: 0x1000100d: mnemonic(mov)
    insn: 0x1000100f: offset(0x1000A7C8)
    insn: 0x1000100f: mnemonic(mov)
    insn: 0x10001015: offset(0x100075C8)
    insn: 0x10001015: mnemonic(mov)
    insn: 0x1000101b: mnemonic(mov)
    insn: 0x1000101d: number(0x80)
    insn: 0x1000101d: mnemonic(and)
    insn: 0x10001020: mnemonic(neg)
    insn: 0x10001022: mnemonic(sbb)
    insn: 0x10001024: number(0x1B)
    insn: 0x10001024: mnemonic(and)
    insn: 0x10001027: number(0x1)
    insn: 0x10001027: mnemonic(shl)
    ...
"""
import sys
import logging
import argparse

import capa.main
import capa.rules
import capa.engine
import capa.features
import capa.features.freeze
import capa.features.extractors.viv


def main(argv=None):
    if argv is None:
        argv = sys.argv[1:]

    formats = [
        ("auto", "(default) detect file type automatically"),
        ("pe", "Windows PE file"),
        ("sc32", "32-bit shellcode"),
        ("sc64", "64-bit shellcode"),
        ("freeze", "features previously frozen by capa"),
    ]
    format_help = ", ".join(["%s: %s" % (f[0], f[1]) for f in formats])

    parser = argparse.ArgumentParser(description="Show the features that capa extracts from the given sample")
    parser.add_argument("sample", type=str, help="Path to sample to analyze")
    parser.add_argument(
        "-f", "--format", choices=[f[0] for f in formats], default="auto", help="Select sample format, %s" % format_help
    )
    parser.add_argument("-F", "--function", type=lambda x: int(x, 0x10), help="Show features for specific function")
    args = parser.parse_args(args=argv)

    logging.basicConfig(level=logging.INFO)
    logging.getLogger().setLevel(logging.INFO)

    if args.format == "freeze":
        with open(args.sample, "rb") as f:
            extractor = capa.features.freeze.load(f.read())
    else:
        vw = capa.main.get_workspace(args.sample, args.format)
        extractor = capa.features.extractors.viv.VivisectFeatureExtractor(vw, args.sample)

    if not args.function:
        for feature, va in extractor.extract_file_features():
            if va:
                print("file: 0x%08x: %s" % (va, feature))
            else:
                print("file: 0x00000000: %s" % (feature))

    functions = extractor.get_functions()

    if args.function:
        if args.format == "freeze":
            functions = filter(lambda f: f == args.function, functions)
        else:
            functions = filter(lambda f: f.va == args.function, functions)

            if args.function not in [f.va for f in functions]:
                print("0x%X not a function, creating it" % args.function)
                vw.makeFunction(args.function)
                functions = extractor.get_functions()
                functions = filter(lambda f: f.va == args.function, functions)

        if len(functions) == 0:
            print("0x%X not a function")
            return -1

    print_features(functions, extractor)

    return 0


def ida_main():
    function = idc.get_func_attr(idc.here(), idc.FUNCATTR_START)
    print("getting features for current function 0x%X" % function)

    extractor = capa.features.extractors.ida.IdaFeatureExtractor()

    if not function:
        for feature, va in extractor.extract_file_features():
            if va:
                print("file: 0x%08x: %s" % (va, feature))
            else:
                print("file: 0x00000000: %s" % (feature))
        return

    functions = extractor.get_functions()

    if function:
        functions = filter(lambda f: f.start_ea == function, functions)

        if len(functions) == 0:
            print("0x%X not a function" % function)
            return -1

    print_features(functions, extractor)

    return 0


def print_features(functions, extractor):
    for f in functions:
        for feature, va in extractor.extract_function_features(f):
            print("func: 0x%08x: %s" % (va, feature))

        for bb in extractor.get_basic_blocks(f):
            for feature, va in extractor.extract_basic_block_features(f, bb):
                print("bb  : 0x%08x: %s" % (va, feature))

            for insn in extractor.get_instructions(f, bb):
                for feature, va in extractor.extract_insn_features(f, bb, insn):
                    try:
                        print("insn: 0x%08x: %s" % (va, feature))
                    except UnicodeEncodeError:
                        # may be an issue while piping to less and encountering non-ascii characters
                        continue


if __name__ == "__main__":
    if capa.main.is_runtime_ida():
        ida_main()
    else:
        sys.exit(main())