A heap overflow in base64.c:86

[seviezhou]

System info

Ubuntu x86_64, gcc (Ubuntu 5.5.0-12ubuntu1), dmg2img (latest master f16f24)

Command line

./dmg2img -i @@ -o /dev/null

Output

Segmentation fault

AddressSanitizer output

=================================================================
==35628==ERROR: AddressSanitizer: heap-buffer-overflow on address 0x60200000efef at pc 0x00000040e763 bp 0x7fff07749610 sp 0x7fff07749600
READ of size 1 at 0x60200000efef thread T0
    #0 0x40e762 in decode_base64 /home/seviezhou/dmg2img/base64.c:86
    #1 0x403327 in main /home/seviezhou/dmg2img/dmg2img.c:273
    #2 0x7fcf3a12383f in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x2083f)
    #3 0x408108 in _start (/home/seviezhou/dmg2img/dmg2img+0x408108)

0x60200000efef is located 1 bytes to the left of 5-byte region [0x60200000eff0,0x60200000eff5)
allocated by thread T0 here:
    #0 0x7fcf3a98f602 in malloc (/usr/lib/x86_64-linux-gnu/libasan.so.2+0x98602)
    #1 0x40322d in main /home/seviezhou/dmg2img/dmg2img.c:265

SUMMARY: AddressSanitizer: heap-buffer-overflow /home/seviezhou/dmg2img/base64.c:86 decode_base64
Shadow bytes around the buggy address:
  0x0c047fff9da0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c047fff9db0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c047fff9dc0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c047fff9dd0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c047fff9de0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
=>0x0c047fff9df0: fa fa fa fa fa fa fa fa fa fa fa fa fa[fa]05 fa
  0x0c047fff9e00: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c047fff9e10: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c047fff9e20: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c047fff9e30: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c047fff9e40: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
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
  Heap right redzone:      fb
  Freed heap region:       fd
  Stack left redzone:      f1
  Stack mid redzone:       f2
  Stack right redzone:     f3
  Stack partial redzone:   f4
  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
==35628==ABORTING

POC

heap-overflow-decode_base64-base64-86.zip