An issue was discovered in gpac through 20200801. A NULL pointer dereference exists in the function ilst_item_box_dump located in box_dump.c. It allows an attacker to cause Denial of Service.
## System info

Ubuntu x86_64, gcc (Ubuntu 5.5.0-12ubuntu1), MP4Box (latest master [2aa266](https://github.com/gpac/gpac/commit/2aa266dfaab6aaad9f9f4f216ad7d1e62adc7fa0))

## Configure

CFLAGS="-g -fsanitize=address" LDFLAGS="-fsanitize=address" ./configure --static-mp4box

## Command line

./bin/gcc/MP4Box -diso -out /dev/null @@

## AddressSanitizer output

```
ASAN:SIGSEGV
=================================================================
==77583==ERROR: AddressSanitizer: SEGV on unknown address 0x000000000038 (pc 0x555d67a9030a bp 0x61600000cf80 sp 0x7ffc245f5240 T0)
    #0 0x555d67a90309 in ilst_item_box_dump isomedia/box_dump.c:3641
    #1 0x555d67ac2749 in gf_isom_box_dump isomedia/box_funcs.c:1923
    #2 0x555d67a6caba in gf_isom_dump isomedia/box_dump.c:135
    #3 0x555d67449ce9 in dump_isom_xml /home/seviezhou/gpac/applications/mp4box/filedump.c:1670
    #4 0x555d6741afa4 in mp4boxMain /home/seviezhou/gpac/applications/mp4box/main.c:5548
    #5 0x7fe303b6bb96 in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x21b96)
    #6 0x555d673f8f09 in _start (/home/seviezhou/gpac/bin/gcc/MP4Box+0x27ff09)

AddressSanitizer can not provide additional info.
SUMMARY: AddressSanitizer: SEGV isomedia/box_dump.c:3641 ilst_item_box_dump
==77583==ABORTING
```

## POC

[SEGV-ilst_item_box_dump-box_dump-3641.zip](https://github.com/gpac/gpac/files/5066977/SEGV-ilst_item_box_dump-box_dump-3641.zip)

A Segmentation fault in box_dump.c:3641
This is a GitHub Issue
repo:gpac
owner:gpac
Title : A Segmentation fault in box_dump.c:3641
Issue date:

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## System info

Ubuntu x86_64, gcc (Ubuntu 5.5.0-12ubuntu1), MP4Box (latest master [2aa266](https://github.com/gpac/gpac/commit/2aa266dfaab6aaad9f9f4f216ad7d1e62adc7fa0))

## Configure

CFLAGS="-g -fsanitize=address" LDFLAGS="-fsanitize=address" ./configure --static-mp4box

## Command line

./bin/gcc/MP4Box -diso -out /dev/null @@

## AddressSanitizer output

```
ASAN:SIGSEGV
=================================================================
==77583==ERROR: AddressSanitizer: SEGV on unknown address 0x000000000038 (pc 0x555d67a9030a bp 0x61600000cf80 sp 0x7ffc245f5240 T0)
    #0 0x555d67a90309 in ilst_item_box_dump isomedia/box_dump.c:3641
    #1 0x555d67ac2749 in gf_isom_box_dump isomedia/box_funcs.c:1923
    #2 0x555d67a6caba in gf_isom_dump isomedia/box_dump.c:135
    #3 0x555d67449ce9 in dump_isom_xml /home/seviezhou/gpac/applications/mp4box/filedump.c:1670
    #4 0x555d6741afa4 in mp4boxMain /home/seviezhou/gpac/applications/mp4box/main.c:5548
    #5 0x7fe303b6bb96 in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x21b96)
    #6 0x555d673f8f09 in _start (/home/seviezhou/gpac/bin/gcc/MP4Box+0x27ff09)

AddressSanitizer can not provide additional info.
SUMMARY: AddressSanitizer: SEGV isomedia/box_dump.c:3641 ilst_item_box_dump
==77583==ABORTING
```

## POC

[SEGV-ilst_item_box_dump-box_dump-3641.zip](https://github.com/gpac/gpac/files/5066977/SEGV-ilst_item_box_dump-box_dump-3641.zip)

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