국내에서 발생한 안드로이드 악성코드 중 개인적으로 가장 진보된? 난독화 기술을 사용한 카카오톡 보안 플러그인 악성코드를 소개하고 싶다.

카카오톡 보안 플러그인이라는 악성코드는 국내 안드로이드 개발자 컴퓨터를 해킹하여 구글플레이에 업로드 되어 2013년 6월 30일에 유포된 것으로 알려져 있다.

허나 개발자 계정 해킹으로는 구글마켓 업로드는 불가능하며 keystore 비밀번호 등등  등록된 컴퓨터에서만 업로드가 가능하다고 한다~ 해킹일지 아니면 개발자가 큰돈 받고 올린건지...


참고 http://erteam.nprotect.com/428  

분석보고서 http://training.nshc.net/KOR/Document/isac/20130630_KakaoTalk_Plug-in_Malware_1.1.pdf


JNI를 사용하는 악성코드가 언젠간 나오겠지~ 라고 생각하다 정말 나와버렸다. 


ddd

<Fig1. AndroidManifest.xml>



정직하게 MainActivity 에서 따라가보면



<Fig2. MainActivitiy.class>

???????이게 끝????



<Fig3. MoriService.class>

Manifest의 Serivce에서 MoriService.class가 정의되어 Service로 앱 실행 시  Eglsv1.so 를 호출하여 Handle 생성 후 ReadDAT()를 호출한다. 



<Fig4. Eglsv1.so>

ReadDAT을 보면 참 아름답다.



<Fig5. Encrypted String>




음...................문자열이 암호화 되었군.............


ida가 뭐하는건데 킨 거지?


음...


내가 arm을 알았던가?


음...


아톰시피유가 뭐죠?




긴글 봐주셔서 감사합니다.

























는 훼이끄...




<Fig6. Decryption Function >


암호 루틴을 찾고 따라가보니 바로~~~~ 

rijndael192  + xor 연산으로 암호화 되어있었다~


ex) RAINEBQBQVkKiAwEs9VWPODaejQh3TFn1jpcS9ztCX

R     A      INEBQBQV            kKiAwEs9VWPODaejQh3TFn1jpcS9ztCX

XOR key     Rijndael192 key    Rijndael192 CipherText


자 이제 파이썬으로 구현해보자

# ported from the Java reference code by Bram Cohen, bram@gawth.com, April 2001
# this code is public domain, unless someone makes
# an intellectual property claim against the reference
# code, in which case it can be made public domain by
# deleting all the comments and renaming all the variables
 
import copy
import string
import base64
 
 
#-----------------------
#TREV - ADDED BECAUSE THERE'S WARNINGS ABOUT INT OVERFLOW BEHAVIOR CHANGING IN
#2.4.....
import os
if os.name != "java":
    import exceptions
    if hasattr(exceptions, "FutureWarning"):
        import warnings
        warnings.filterwarnings("ignore", category=FutureWarning, append=1)
#-----------------------
 
 
 
shifts = [[[0, 0], [1, 3], [2, 2], [3, 1]],
          [[0, 0], [1, 5], [2, 4], [3, 3]],
          [[0, 0], [1, 7], [3, 5], [4, 4]]]
 
# [keysize][block_size]
num_rounds = {16: {16: 10, 24: 12, 32: 14}, 24: {16: 12, 24: 12, 32: 14}, 32: {16: 14, 24: 14, 32: 14}}
 
A = [[1, 1, 1, 1, 1, 0, 0, 0],
     [0, 1, 1, 1, 1, 1, 0, 0],
     [0, 0, 1, 1, 1, 1, 1, 0],
     [0, 0, 0, 1, 1, 1, 1, 1],
     [1, 0, 0, 0, 1, 1, 1, 1],
     [1, 1, 0, 0, 0, 1, 1, 1],
     [1, 1, 1, 0, 0, 0, 1, 1],
     [1, 1, 1, 1, 0, 0, 0, 1]]
 
# produce log and alog tables, needed for multiplying in the
# field GF(2^m) (generator = 3)
alog = [1]
for i in xrange(255):
    j = (alog[-1] << 1) ^ alog[-1]
    if j & 0x100 != 0:
        j ^= 0x11B
    alog.append(j)
 
log = [0] * 256
for i in xrange(1, 255):
    log[alog[i]] = i
 
# multiply two elements of GF(2^m)
def mul(a, b):
    if a == 0 or b == 0:
        return 0
    return alog[(log[a & 0xFF] + log[b & 0xFF]) % 255]
 
# substitution box based on F^{-1}(x)
box = [[0] * 8 for i in xrange(256)]
box[1][7] = 1
for i in xrange(2, 256):
    j = alog[255 - log[i]]
    for t in xrange(8):
        box[i][t] = (j >> (7 - t)) & 0x01
 
B = [0, 1, 1, 0, 0, 0, 1, 1]
 
# affine transform:  box[i] <- B + A*box[i]
cox = [[0] * 8 for i in xrange(256)]
for i in xrange(256):
    for t in xrange(8):
        cox[i][t] = B[t]
        for j in xrange(8):
            cox[i][t] ^= A[t][j] * box[i][j]
 
# S-boxes and inverse S-boxes
S =  [0] * 256
Si = [0] * 256
for i in xrange(256):
    S[i] = cox[i][0] << 7
    for t in xrange(1, 8):
        S[i] ^= cox[i][t] << (7-t)
    Si[S[i] & 0xFF] = i
 
# T-boxes
G = [[2, 1, 1, 3],
    [3, 2, 1, 1],
    [1, 3, 2, 1],
    [1, 1, 3, 2]]
 
AA = [[0] * 8 for i in xrange(4)]
 
for i in xrange(4):
    for j in xrange(4):
        AA[i][j] = G[i][j]
        AA[i][i+4] = 1
 
for i in xrange(4):
    pivot = AA[i][i]
    if pivot == 0:
        t = i + 1
        while AA[t][i] == 0 and t < 4:
            t += 1
            assert t != 4, 'G matrix must be invertible'
            for j in xrange(8):
                AA[i][j], AA[t][j] = AA[t][j], AA[i][j]
            pivot = AA[i][i]
    for j in xrange(8):
        if AA[i][j] != 0:
            AA[i][j] = alog[(255 + log[AA[i][j] & 0xFF] - log[pivot & 0xFF]) % 255]
    for t in xrange(4):
        if i != t:
            for j in xrange(i+1, 8):
                AA[t][j] ^= mul(AA[i][j], AA[t][i])
            AA[t][i] = 0
 
iG = [[0] * 4 for i in xrange(4)]
 
for i in xrange(4):
    for j in xrange(4):
        iG[i][j] = AA[i][j + 4]
 
def mul4(a, bs):
    if a == 0:
        return 0
    r = 0
    for b in bs:
        r <<= 8
        if b != 0:
            r = r | mul(a, b)
    return r
 
T1 = []
T2 = []
T3 = []
T4 = []
T5 = []
T6 = []
T7 = []
T8 = []
U1 = []
U2 = []
U3 = []
U4 = []
 
for t in xrange(256):
    s = S[t]
    T1.append(mul4(s, G[0]))
    T2.append(mul4(s, G[1]))
    T3.append(mul4(s, G[2]))
    T4.append(mul4(s, G[3]))
 
    s = Si[t]
    T5.append(mul4(s, iG[0]))
    T6.append(mul4(s, iG[1]))
    T7.append(mul4(s, iG[2]))
    T8.append(mul4(s, iG[3]))
 
    U1.append(mul4(t, iG[0]))
    U2.append(mul4(t, iG[1]))
    U3.append(mul4(t, iG[2]))
    U4.append(mul4(t, iG[3]))
 
# round constants
rcon = [1]
r = 1
for t in xrange(1, 30):
    r = mul(2, r)
    rcon.append(r)
 
del A
del AA
del pivot
del B
del G
del box
del log
del alog
del i
del j
del r
del s
del t
del mul
del mul4
del cox
del iG
 
class rijndael:
    def __init__(self, key, block_size = 16):
        if block_size != 16 and block_size != 24 and block_size != 32:
            raise ValueError('Invalid block size: ' + str(block_size))
        if len(key) != 16 and len(key) != 24 and len(key) != 32:
            raise ValueError('Invalid key size: ' + str(len(key)))
        self.block_size = block_size
 
        ROUNDS = num_rounds[len(key)][block_size]
        BC = block_size / 4
        # encryption round keys
        Ke = [[0] * BC for i in xrange(ROUNDS + 1)]
        # decryption round keys
        Kd = [[0] * BC for i in xrange(ROUNDS + 1)]
        ROUND_KEY_COUNT = (ROUNDS + 1) * BC
        KC = len(key) / 4
 
        # copy user material bytes into temporary ints
        tk = []
        for i in xrange(0, KC):
            tk.append((ord(key[i * 4]) << 24) | (ord(key[i * 4 + 1]) << 16) |
                (ord(key[i * 4 + 2]) << 8) | ord(key[i * 4 + 3]))
 
        # copy values into round key arrays
        t = 0
        j = 0
        while j < KC and t < ROUND_KEY_COUNT:
            Ke[t / BC][t % BC] = tk[j]
            Kd[ROUNDS - (t / BC)][t % BC] = tk[j]
            j += 1
            t += 1
        tt = 0
        rconpointer = 0
        while t < ROUND_KEY_COUNT:
            # extrapolate using phi (the round key evolution function)
            tt = tk[KC - 1]
            tk[0] ^= (S[(tt >> 16) & 0xFF] & 0xFF) << 24 ^  \
                     (S[(tt >>  8) & 0xFF] & 0xFF) << 16 ^  \
                     (S[ tt        & 0xFF] & 0xFF) <<  8 ^  \
                     (S[(tt >> 24) & 0xFF] & 0xFF)       ^  \
                     (rcon[rconpointer]    & 0xFF) << 24
            rconpointer += 1
            if KC != 8:
                for i in xrange(1, KC):
                    tk[i] ^= tk[i-1]
            else:
                for i in xrange(1, KC / 2):
                    tk[i] ^= tk[i-1]
                tt = tk[KC / 2 - 1]
                tk[KC / 2] ^= (S[ tt        & 0xFF] & 0xFF)       ^ \
                              (S[(tt >>  8) & 0xFF] & 0xFF) <<  8 ^ \
                              (S[(tt >> 16) & 0xFF] & 0xFF) << 16 ^ \
                              (S[(tt >> 24) & 0xFF] & 0xFF) << 24
                for i in xrange(KC / 2 + 1, KC):
                    tk[i] ^= tk[i-1]
            # copy values into round key arrays
            j = 0
            while j < KC and t < ROUND_KEY_COUNT:
                Ke[t / BC][t % BC] = tk[j]
                Kd[ROUNDS - (t / BC)][t % BC] = tk[j]
                j += 1
                t += 1
        # inverse MixColumn where needed
        for r in xrange(1, ROUNDS):
            for j in xrange(BC):
                tt = Kd[r][j]
                Kd[r][j] = U1[(tt >> 24) & 0xFF] ^ \
                           U2[(tt >> 16) & 0xFF] ^ \
                           U3[(tt >>  8) & 0xFF] ^ \
                           U4[ tt        & 0xFF]
        self.Ke = Ke
        self.Kd = Kd
 
    def encrypt(self, plaintext):
        if len(plaintext) != self.block_size:
            raise ValueError('wrong block length, expected ' + str(self.block_size) + ' got ' + str(len(plaintext)))
        Ke = self.Ke
 
        BC = self.block_size / 4
        ROUNDS = len(Ke) - 1
        if BC == 4:
            SC = 0
        elif BC == 6:
            SC = 1
        else:
            SC = 2
        s1 = shifts[SC][1][0]
        s2 = shifts[SC][2][0]
        s3 = shifts[SC][3][0]
        a = [0] * BC
        # temporary work array
        t = []
        # plaintext to ints + key
        for i in xrange(BC):
            t.append((ord(plaintext[i * 4    ]) << 24 |
                      ord(plaintext[i * 4 + 1]) << 16 |
                      ord(plaintext[i * 4 + 2]) <<  8 |
                      ord(plaintext[i * 4 + 3])        ) ^ Ke[0][i])
        # apply round transforms
        for r in xrange(1, ROUNDS):
            for i in xrange(BC):
                a[i] = (T1[(t[ i           ] >> 24) & 0xFF] ^
                        T2[(t[(i + s1) % BC] >> 16) & 0xFF] ^
                        T3[(t[(i + s2) % BC] >>  8) & 0xFF] ^
                        T4[ t[(i + s3) % BC]        & 0xFF]  ) ^ Ke[r][i]
            t = copy.copy(a)
        # last round is special
        result = []
        for i in xrange(BC):
            tt = Ke[ROUNDS][i]
            result.append((S[(t[ i           ] >> 24) & 0xFF] ^ (tt >> 24)) & 0xFF)
            result.append((S[(t[(i + s1) % BC] >> 16) & 0xFF] ^ (tt >> 16)) & 0xFF)
            result.append((S[(t[(i + s2) % BC] >>  8) & 0xFF] ^ (tt >>  8)) & 0xFF)
            result.append((S[ t[(i + s3) % BC]        & 0xFF] ^  tt       ) & 0xFF)
        return string.join(map(chr, result), '')
 
    def decrypt(self, ciphertext):
        if len(ciphertext) != self.block_size:
            raise ValueError('wrong block length, expected ' + str(self.block_size) + ' got ' + str(len(plaintext)))
        Kd = self.Kd
 
        BC = self.block_size / 4
        ROUNDS = len(Kd) - 1
        if BC == 4:
            SC = 0
        elif BC == 6:
            SC = 1
        else:
            SC = 2
        s1 = shifts[SC][1][1]
        s2 = shifts[SC][2][1]
        s3 = shifts[SC][3][1]
        a = [0] * BC
        # temporary work array
        t = [0] * BC
        # ciphertext to ints + key
        for i in xrange(BC):
            t[i] = (ord(ciphertext[i * 4    ]) << 24 |
                    ord(ciphertext[i * 4 + 1]) << 16 |
                    ord(ciphertext[i * 4 + 2]) <<  8 |
                    ord(ciphertext[i * 4 + 3])        ) ^ Kd[0][i]
        # apply round transforms
        for r in xrange(1, ROUNDS):
            for i in xrange(BC):
                a[i] = (T5[(t[ i           ] >> 24) & 0xFF] ^
                        T6[(t[(i + s1) % BC] >> 16) & 0xFF] ^
                        T7[(t[(i + s2) % BC] >>  8) & 0xFF] ^
                        T8[ t[(i + s3) % BC]        & 0xFF]  ) ^ Kd[r][i]
            t = copy.copy(a)
        # last round is special
        result = []
        for i in xrange(BC):
            tt = Kd[ROUNDS][i]
            result.append((Si[(t[ i           ] >> 24) & 0xFF] ^ (tt >> 24)) & 0xFF)
            result.append((Si[(t[(i + s1) % BC] >> 16) & 0xFF] ^ (tt >> 16)) & 0xFF)
            result.append((Si[(t[(i + s2) % BC] >>  8) & 0xFF] ^ (tt >>  8)) & 0xFF)
            result.append((Si[ t[(i + s3) % BC]        & 0xFF] ^  tt       ) & 0xFF)
        return string.join(map(chr, result), '')
 
def decrypt(key, encoded):
    padded_key = key.ljust(16, "\0")
    ciphertext = base64.b64decode(encoded)
    r = rijndael(padded_key, 24)
    padded_text = ""
    for start in range(0, len(ciphertext), 24):
        padded_text += r.decrypt(ciphertext[start:start+24])
    plaintext = padded_text.split("\x00", 1)[0]
    return plaintext
 
#antivirus
listcipher =["RAINEBQBQVkKiAwEs9VWPODaejQh3TFn1jpcS9ztCX","EOAZSDCFEJPfxIxidWIbTZZhRr2S93AV7Yp3QNsb6z",
            "LREZSDYTKJV25RUXuaGaYxFh2KEkKK56QrHZmY5e2q","OAIPAHUDEJ0vxHNfSV8c2JRz4eVzhlYAQlbnq8JXw9",
            "HXIPORYFQRQuAesYG1S6EEFrYdn6aNiRBA1IHGg4IT","NSYPQDUDSDTSmgLN1wAzssSl67lhAbT5DimAHhHCqC",
            "OPEBMDUPSXAspKQCk9szNWNQfNMTbM1mzWTvvp7WaF","TAOVSLSXSVGnsP8nXvrxfh5v0UHS07LtkaP1KV0AFz",
            "BSMTQHCRQPxanYLQfvfuvGVNDv4FAtWsOx5WAL12Kr","ASKLELIJGFH2hVPH4Z3Og4bxxFNoSQeNDvaGZagz0n",
            "MBHGFABMTGozpXfPpWzm1gdQBjuGoDCve5MSFH96juSwt6Q1Dg8XX9yTTHVnC4hDcJBoazVL7a","GOZAZMNOLSQnxZiJ5NLQmQ46mGbJZjwIORoKy62gDA",
            "HLHADWZKBMZLiXM1RvbljIGPwhH8MugKzVxE1UehWV","XMLSLGZMLSjQ6rUtct4zB2L2pduxajx64YgU0ZHWUATPUYCVT6kKC4VnB3KmKRpokvWb6oxnzT",
            "YRRADOXOLOrPn117W4R7xlTzgZeP54RNQd5qvRUMGyaX4duLH1Bxa2miWSaAeaeODR7RDTytqd","CDTGVSXUDSZRhuNHOo9JH1HIMm2dhOd89mxMM1nk6A",
            "VBFMVQZMLEDBWNKvBDPv8NEbarx0mryt7oq7JTX7Kn","BAPYNONKHKE7Co6zfGHY8vOxtJM9iga6KQtrMDjskj",
            "RVFCVAXWXEwQAc0Va4Mt5pC1v6E4I4AHIGkR08eW7n0JcxbQwEDTFtyqdYJhmLJf4qG0dRiBxP","QVPGHGLOPE9HUz2cdW0iAu6ZcMP9DiKfKiss2EvdGF"]


for i in range (len(listcipher)):
        chipertxt=listcipher[i]
        oneround = decrypt(chipertxt[2:10], chipertxt[10:])
        xorkey= chr(ord(chipertxt[0]) ^ 0x0a)
        plaintext=''
        for c in oneround:
            plaintext += chr(ord(c) ^ ord(xorkey))
        print plaintext
        

<Fig7. String Decryption >

Decryption하니 백신사 패키지 명이 보인다~


이젠 안드로이드 악성코드도 백신 공격 시대 ㅎㄷㄷ


<Fig8. Http Authorization>


이 녀석... 통신도 한다. 

  if(authstatus->picked == CURLAUTH_BASIC) {
    /* Basic */
    if((proxy && conn->bits.proxy_user_passwd &&
       !Curl_checkheaders(data, "Proxy-authorization:")) ||
       (!proxy && conn->bits.user_passwd &&
       !Curl_checkheaders(data, "Authorization:"))) {
      auth="Basic";
      result = http_output_basic(conn, proxy);
      if(result)
        return result;
    }



또 하나 재미있는 부분

<Fig9. Apk>


쟤 뱃속에 APK가 들어있어요!!!!

<Fig10. WriteFile>

/system/app/FOTAKill.apk로 저장된다


<Fig11. dump.apk>

긁은 파일 정보

https://www.virustotal.com/en/file/141652d4d44143d232a35180f704d1c1c9b0b33049ebbe19026d6b1d978790ab/analysis/ 



JNI를 사용하여 스트링 난독화로 안티 역공학에...백신 확인, 드롭퍼 역할까지.... 


아무튼 JNI를 활용하면 기존 바이너리에 쓰이던 코드 난독화 기법을 사용할 수 있게된다. (ex api 리다이렉션, 더미 코드 삽입  등등) 

참 무궁무진하므로  안드로이드 분석도 이젠 ㅠㅠ




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Posted by kkoha 트랙백 0 : 댓글 4

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