Created attachment 14217 [details]
Reproducer.

Build Information:
Wireshark git master.
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The following crash due to a stack-based buffer overflow can be observed in an ASAN build of Wireshark (current git master), by feeding a malformed file to tshark ("$ ./tshark -nVxr /path/to/file"):

Attached is a file which triggers the crash.

--- cut ---
==25088==ERROR: AddressSanitizer: stack-buffer-overflow on address 0x7fffdbb9f36e at pc 0x7f26c4ae2af4 bp 0x7fffdbb9f190 sp 0x7fffdbb9f188
READ of size 1 at 0x7fffdbb9f36e thread T0
    #0 0x7f26c4ae2af3 in ascii_strup_inplace wireshark/wsutil/str_util.c:71:16
    #1 0x7f26d8893b1c in iseries_check_file_type wireshark/wiretap/iseries.c:336:9
    #2 0x7f26d8892a63 in iseries_open wireshark/wiretap/iseries.c:231:14
    #3 0x7f26d8864c51 in wtap_open_offline wireshark/wiretap/file_access.c:1042:13
    #4 0x51dd9d in cf_open wireshark/tshark.c:4195:9
    #5 0x5178cb in main wireshark/tshark.c:2188:9

Address 0x7fffdbb9f36e is located in stack of thread T0 at offset 302 in frame
    #0 0x7f26d88934bf in iseries_check_file_type wireshark/wiretap/iseries.c:306

  This frame has 2 object(s):
    [32, 302) 'buf' <== Memory access at offset 302 overflows this variable
    [368, 377) 'protocol'
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 wireshark/wsutil/str_util.c:71:16 in ascii_strup_inplace
Shadow bytes around the buggy address:
  0x10007b76be10: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x10007b76be20: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x10007b76be30: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x10007b76be40: 00 00 00 00 00 00 00 00 f1 f1 f1 f1 00 00 00 00
  0x10007b76be50: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
=>0x10007b76be60: 00 00 00 00 00 00 00 00 00 00 00 00 00[06]f2 f2
  0x10007b76be70: f2 f2 f2 f2 f2 f2 00 01 f3 f3 f3 f3 00 00 00 00
  0x10007b76be80: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x10007b76be90: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x10007b76bea0: 00 00 00 00 00 00 00 00 00 00 00 00 f1 f1 f1 f1
  0x10007b76beb0: 00 00 00 00 00 00 00 00 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
  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
  Left alloca redzone:     ca
  Right alloca redzone:    cb
==25088==ABORTING
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This bug is subject to a 90 day disclosure deadline. If 90 days elapse without a broadly available patch, then the bug report will automatically become visible to the public.