ytnef: heap-based buffer overflow in PrintTNEF (ytnefprint/main.c)

["Agostino Sarubbo" <ago () gentoo org>]

Not security relevant at all since the crash happens in the command line tool, but I'm sharing it as well.

Description:
ytnef is Yeraze’s TNEF Stream Reader – for winmail.dat files.

The complete ASan output of the issue:

# ytnefprint $FILE
==11928==ERROR: AddressSanitizer: heap-buffer-overflow on address 0x602000001031 at pc 0x00000049df8d bp 0x7ffd1e1feb20 
sp 0x7ffd1e1fe2d0
READ of size 2 at 0x602000001031 thread T0
    #0 0x49df8c in printf_common(void*, char const*, __va_list_tag*) 
/tmp/portage/sys-libs/compiler-rt-sanitizers-4.0.0/work/compiler-rt-4.0.0.src/lib/asan/../sanitizer_common/sanitizer_common_interceptors_format.inc:544
    #1 0x49ea7a in __interceptor_vprintf 
/tmp/portage/sys-libs/compiler-rt-sanitizers-4.0.0/work/compiler-rt-4.0.0.src/lib/asan/../sanitizer_common/sanitizer_common_interceptors.inc:1388
    #2 0x49eb37 in printf 
/tmp/portage/sys-libs/compiler-rt-sanitizers-4.0.0/work/compiler-rt-4.0.0.src/lib/asan/../sanitizer_common/sanitizer_common_interceptors.inc:1434
    #3 0x509747 in PrintTNEF /tmp/ytnef-1.9.2/ytnefprint/main.c:195:7
    #4 0x50882e in main /tmp/ytnef-1.9.2/ytnefprint/main.c:84:5
    #5 0x7f16830da78f in __libc_start_main 
/tmp/portage/sys-libs/glibc-2.23-r3/work/glibc-2.23/csu/../csu/libc-start.c:289
    #6 0x419c38 in _start (/usr/bin/ytnefprint+0x419c38)

0x602000001031 is located 0 bytes to the right of 1-byte region [0x602000001030,0x602000001031)
allocated by thread T0 here:
    #0 0x4cf7e0 in calloc 
/tmp/portage/sys-libs/compiler-rt-sanitizers-4.0.0/work/compiler-rt-4.0.0.src/lib/asan/asan_malloc_linux.cc:74
    #1 0x7f1683faf8bb in TNEFAttachmentFilename /tmp/ytnef-1.9.2/lib/ytnef.c:752:19
    #2 0x7f1683fc5b47 in TNEFParse /tmp/ytnef-1.9.2/lib/ytnef.c:1184:15
    #3 0x7f1683fc49d3 in TNEFParseFile /tmp/ytnef-1.9.2/lib/ytnef.c:1042:10
    #4 0x508814 in main /tmp/ytnef-1.9.2/ytnefprint/main.c:80:9
    #5 0x7f16830da78f in __libc_start_main 
/tmp/portage/sys-libs/glibc-2.23-r3/work/glibc-2.23/csu/../csu/libc-start.c:289

SUMMARY: AddressSanitizer: heap-buffer-overflow 
/tmp/portage/sys-libs/compiler-rt-sanitizers-4.0.0/work/compiler-rt-4.0.0.src/lib/asan/../sanitizer_common/sanitizer_common_interceptors_format.inc:544
 in 
printf_common(void*, char const*, __va_list_tag*)
Shadow bytes around the buggy address:
  0x0c047fff81b0: fa fa 00 00 fa fa 04 fa fa fa 00 00 fa fa 00 fa
  0x0c047fff81c0: fa fa 00 00 fa fa 00 fa fa fa 00 00 fa fa 04 fa
  0x0c047fff81d0: fa fa 00 00 fa fa 00 05 fa fa 00 00 fa fa 00 00
  0x0c047fff81e0: fa fa 05 fa fa fa 00 00 fa fa 00 05 fa fa 00 00
  0x0c047fff81f0: fa fa 00 00 fa fa fd fd fa fa fd fd fa fa fd fd
=>0x0c047fff8200: fa fa fd fa fa fa[01]fa fa fa 00 00 fa fa 04 fa
  0x0c047fff8210: fa fa 00 00 fa fa 04 fa fa fa 00 00 fa fa 04 fa
  0x0c047fff8220: fa fa 00 00 fa fa 04 fa fa fa 00 00 fa fa 00 fa
  0x0c047fff8230: fa fa 00 00 fa fa 00 fa fa fa 00 00 fa fa 04 fa
  0x0c047fff8240: fa fa 00 00 fa fa 00 00 fa fa 00 00 fa fa 01 fa
  0x0c047fff8250: fa fa 00 00 fa fa 00 00 fa fa 00 00 fa fa fd fd
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
==11928==ABORTING
Affected version:
1.9.2

Fixed version:
N/A

Commit fix:
N/A

Credit:
This bug was discovered by Agostino Sarubbo of Gentoo.

CVE:
N/A

Reproducer:
https://github.com/asarubbo/poc/blob/master/00242-ytnef-heapoverflow-PrintTNEF

Timeline:
2017-03-27: bug discovered and reported to upstream
2017-05-24: blog post about the issue

Note:
This bug was found with American Fuzzy Lop.

Permalink:
https://blogs.gentoo.org/ago/2017/05/24/ytnef-heap-based-buffer-overflow-in-printtnef-ytnefprintmain-c/

--
Agostino Sarubbo
Gentoo Linux Developer