# Detecting Formbook for Volatility
#
# LICENSE
# Please refer to the LICENSE.txt in the https://github.com/JPCERTCC/MalConfScan/
#
# How to use:
# 1. cd "Volatility Folder"
# 2. mv formbookscan.py volatility/plugins/malware
# 3. python vol.py formbookconfig -f images.mem --profile=Win7SP1x64

import volatility.plugins.taskmods as taskmods
import volatility.win32.tasks as tasks
import volatility.utils as utils
import volatility.debug as debug
import volatility.plugins.malware.malfind as malfind
import re
import pefile
from Crypto.Hash import SHA
from struct import unpack, unpack_from, pack
from collections import OrderedDict
from formbook_decryption import FormBookDecryption

try:
    import yara
    has_yara = True
except ImportError:
    has_yara = False

formbook_sig = {
    'namespace1' : 'rule Formbook { \
                    strings: \
                       $sqlite3step = { 68 34 1c 7b e1 } \
                       $sqlite3text = { 68 38 2a 90 c5 } \
                       $sqlite3blob = { 68 53 d8 7f 8c } \
                    condition: all of them}'
}

# Config pattern
CONFIG_PATTERNS = [re.compile("\x83\xc4\x0c\x6a\x14\xe8(....)\x83\xc0\x02\x50\x8d(..)\x51\xe8(....)\x83\xc4\x0c\x6a\x14\xe8(....)\x83\xc0\x02\x50\x8d(..)\x52", re.DOTALL)]

# Hashs pattern
HASHS_PATTERNS = [re.compile("\x68(.)(\x02|\x03)\x00\x00\x8d(...)\x00\x00\xe8", re.DOTALL)]

# Strings pattern
STRINGS_PATTERNS = [re.compile("\x6a\x00\x50\xc6\x85(....)\x00\xe8(....)\x83\xc4\x0c\x68(..)\x00\x00\xe8", re.DOTALL)]


class formbookConfig(taskmods.DllList):
    """Parse the Formbook configuration"""

    @staticmethod
    def is_valid_profile(profile):
        return (profile.metadata.get('os', 'unknown') == 'windows'), profile.metadata.get('memory_model', '32bit')

    def get_vad_base(self, task, address):
        for vad in task.VadRoot.traverse():
            if address >= vad.Start and address < vad.End:
                return vad.Start, vad.End

        return None

    def sha1_revert(self, digest):
        tuples = unpack("<IIIII", digest)
        output_hash = ""
        for item in tuples:
            output_hash += pack(">I", item)
        return output_hash

    def formbook_compute_sha1(self, input_buffer):
        sha1 = SHA.new()
        sha1.update(input_buffer)
        return self.sha1_revert(sha1.digest())

    def formbook_decrypt_strings(self, fb_decrypt, p_data, key, encrypted_strings):
        offset = 0
        i = 0
        while offset < len(encrypted_strings):
            str_len = ord(encrypted_strings[offset])
            offset += 1
            dec_str = fb_decrypt.decrypt_func2(encrypted_strings[offset:offset + str_len], key)
            dec_str = dec_str[:-1]  # remove '\0' character
            p_data["Encoded string " + str(i)] = dec_str
            offset += str_len
            i += 1

        return p_data

    def formbook_decrypt(self, key1, key2, config, config_size, strings_data, strings_size, url_size, hashs_data, hashs_size):
        fb_decrypt = FormBookDecryption()
        p_data = OrderedDict()

        rc4_key_one = fb_decrypt.decrypt_func1(key1, 0x14)
        rc4_key_two = fb_decrypt.decrypt_func1(key2, 0x14)
        encbuf2_s1 = fb_decrypt.decrypt_func1(hashs_data, hashs_size)
        encbuf8_s1 = fb_decrypt.decrypt_func1(config, config_size)
        encbuf9_s1 = fb_decrypt.decrypt_func1(strings_data, strings_size)

        rc4_key_1 = self.formbook_compute_sha1(encbuf8_s1)
        rc4_key_2 = self.formbook_compute_sha1(encbuf9_s1)
        rc4_key_3 = self.formbook_compute_sha1(rc4_key_two)
        encbuf2_s2 = fb_decrypt.decrypt_func2(encbuf2_s1, rc4_key_1)
        encbuf8_s2 = fb_decrypt.decrypt_func2(encbuf8_s1, rc4_key_2)

        n = 1
        for i in xrange(config_size):
            encrypted_c2c_uri = encbuf8_s2[i:i + url_size]
            encrypted_c2c_uri = fb_decrypt.decrypt_func2(encrypted_c2c_uri, rc4_key_two)
            c2c_uri = fb_decrypt.decrypt_func2(encrypted_c2c_uri, rc4_key_one)
            if "www." in c2c_uri:
                p_data["C&C URI " + str(n)] = c2c_uri
                n += 1

        encrypted_hashes_array = fb_decrypt.decrypt_func2(encbuf2_s2, rc4_key_3)
        rc4_key_pre_final = self.formbook_compute_sha1(encrypted_hashes_array)
        rc4_key_final = fb_decrypt.decrypt_func2(rc4_key_two, rc4_key_pre_final)

        p_data = self.formbook_decrypt_strings(fb_decrypt, p_data, rc4_key_final, encbuf9_s1)

        return p_data

    def calculate(self):

        if not has_yara:
            debug.error("Yara must be installed for this plugin")

        addr_space = utils.load_as(self._config)

        os, memory_model = self.is_valid_profile(addr_space.profile)
        if not os:
            debug.error("This command does not support the selected profile.")

        rules = yara.compile(sources=formbook_sig)

        for task in self.filter_tasks(tasks.pslist(addr_space)):
            scanner = malfind.VadYaraScanner(task=task, rules=rules)

            for hit, address in scanner.scan():

                vad_base_addr, end = self.get_vad_base(task, address)
                proc_addr_space = task.get_process_address_space()
                data = proc_addr_space.zread(vad_base_addr, end - vad_base_addr)

                config_data = []
                try:
                    pe = pefile.PE(data=data)
                except:
                    continue

                for pattern in CONFIG_PATTERNS:
                    offset = re.search(pattern, data).start()

                offset += 6
                key1_offset = unpack("=I", data[offset:offset + 4])[0] + offset + 11
                key1 = data[key1_offset:key1_offset + (0x14 * 2)]
                offset += 23
                key2_offset = unpack("=I", data[offset:offset + 4])[0] + offset + 11
                key2 = data[key2_offset:key2_offset + (0x14 * 2)]
                offset += 21
                config_size = unpack("=I", data[offset:offset + 4])[0]
                offset += 5
                config_offset = unpack("=I", data[offset:offset + 4])[0] + offset + 11
                config = data[config_offset:config_offset + (config_size * 2)]
                offset += 33
                url_size = unpack("b", data[offset])[0]

                for pattern in STRINGS_PATTERNS:
                    offset = re.search(pattern, data).start()

                offset += 19
                strings_size = unpack("=I", data[offset:offset + 4])[0]
                offset += 5
                strings_offset = unpack("=I", data[offset:offset + 4])[0] + offset + 11
                strings_data = data[strings_offset:strings_offset + (strings_size * 2)]

                for pattern in HASHS_PATTERNS:
                    offset = re.search(pattern, data).start()

                offset += 1
                hashs_size = unpack("=I", data[offset:offset + 4])[0]
                offset += 11
                hashs_offset = unpack("=I", data[offset:offset + 4])[0] + offset + 11
                hashs_data = data[hashs_offset:hashs_offset + (hashs_size * 2)]

                config_data.append(self.formbook_decrypt(key1, key2, config, config_size, strings_data,
                                                         strings_size, url_size, hashs_data, hashs_size))

                yield task, vad_base_addr, end, hit, memory_model, config_data
                break

    def render_text(self, outfd, data):

        delim = '-' * 70

        for task, start, end, malname, memory_model, config_data in data:
            outfd.write("{0}\n".format(delim))
            outfd.write("Process: {0} ({1})\n\n".format(task.ImageFileName, task.UniqueProcessId))

            outfd.write("[Config Info]\n")
            for p_data in config_data:
                for id, param in p_data.items():
                    outfd.write("{0:<16}: {1}\n".format(id, param))