A Pointer Dereference vulnerability exists in GPAC 1.0.1 in unlink_chunk.isra, which causes a Denial of Service (context-dependent).
Thanks for reporting your issue. Please make sure these boxes are checked before submitting your issue - thank you!

- [Yes ] I looked for a similar issue and couldn't find any.
- [ Yes] I tried with the latest version of GPAC. Installers available at http://gpac.io/downloads/gpac-nightly-builds/
- [ Yes] I give enough information for contributors to reproduce my issue (meaningful title, github labels, platform and compiler, command-line ...). I can share files anonymously with this dropbox: https://www.mediafire.com/filedrop/filedrop_hosted.php?drop=eec9e058a9486fe4e99c33021481d9e1826ca9dbc242a6cfaab0fe95da5e5d95

Detailed guidelines: http://gpac.io/2013/07/16/how-to-file-a-bug-properly/

**Version:**
```
./MP4Box -version
```

**command:**
```
./bin/gcc/MP4Box -hint POC2
```
[POC2.zip](https://github.com/gpac/gpac/files/7763677/POC2.zip)

**Result**
```
segmentation fault
```
**bt**

```
Program received signal SIGSEGV, Segmentation fault.
0x00007ffff754da2f in unlink_chunk (p=p@entry=0x5555555e1480, av=0x7ffff76a0b80 <main_arena>) at malloc.c:1453
1453	malloc.c: No such file or directory.
LEGEND: STACK | HEAP | CODE | DATA | RWX | RODATA
[ REGISTERS ]
 RAX  0x14000007a0
 RBX  0x7ffff76a0b80 (main_arena) ◂— 0x0
 RCX  0x14000007a5
 RDX  0x7ffff76a10b0 (main_arena+1328) —▸ 0x7ffff76a10a0 (main_arena+1312) —▸ 0x7ffff76a1090 (main_arena+1296) —▸ 0x7ffff76a1080 (main_arena+1280) —▸ 0x7ffff76a1070 (main_arena+1264) ◂— ...
 RDI  0x5555555e1480 ◂— 0x8013f76a1f74
 RSI  0x4000
 R8   0x7ffff76a0c10 (main_arena+144) —▸ 0x7ffff76a0c00 (main_arena+128) —▸ 0x5555555e0f10 ◂— 0x1400000014
 R9   0x0
 R10  0x7ffff7e0e94e ◂— ' but no data reference entry found\n'
 R11  0x7ffff76a0be0 (main_arena+96) —▸ 0x5555555e69e0 ◂— 0x0
 R12  0x1400000760
 R13  0x40
 R14  0x14000007a0
 R15  0x2
 RBP  0x38
 RSP  0x7fffffff7e30 —▸ 0x5555555e2a00 ◂— 0x1473746383
 RIP  0x7ffff754da2f (unlink_chunk.isra+15) ◂— cmp    rax, qword ptr [rdi + rax]
[ DISASM ]
 ► 0x7ffff754da2f <unlink_chunk.isra+15>     cmp    rax, qword ptr [rdi + rax]
   0x7ffff754da33 <unlink_chunk.isra+19>     jne    unlink_chunk.isra+191                <unlink_chunk.isra+191>
    ↓
   0x7ffff754dadf <unlink_chunk.isra+191>    lea    rdi, [rip + 0x11f954]
   0x7ffff754dae6 <unlink_chunk.isra+198>    call   malloc_printerr                <malloc_printerr>
 
   0x7ffff754daeb <unlink_chunk.isra+203>    lea    rdi, [rip + 0x123756]
   0x7ffff754daf2 <unlink_chunk.isra+210>    call   malloc_printerr                <malloc_printerr>
 
   0x7ffff754daf7                            nop    word ptr [rax + rax]
   0x7ffff754db00 <malloc_consolidate>       push   r15
   0x7ffff754db02 <malloc_consolidate+2>     lea    rax, [rdi + 0x60]
   0x7ffff754db06 <malloc_consolidate+6>     mov    r15, rdi
   0x7ffff754db09 <malloc_consolidate+9>     push   r14
[ STACK ]
00:0000│ rsp 0x7fffffff7e30 —▸ 0x5555555e2a00 ◂— 0x1473746383
01:0008│     0x7fffffff7e38 —▸ 0x7ffff7550773 (_int_malloc+2947) ◂— cmp    r12, 0x1f
02:0010│     0x7fffffff7e40 —▸ 0x5555555e1480 ◂— 0x8013f76a1f74
03:0018│     0x7fffffff7e48 —▸ 0x7ffff76a0be0 (main_arena+96) —▸ 0x5555555e69e0 ◂— 0x0
04:0020│     0x7fffffff7e50 —▸ 0x7fffffff7e60 ◂— 0x38 /* '8' */
05:0028│     0x7fffffff7e58 ◂— 0xdab84f8dc31ec400
06:0030│     0x7fffffff7e60 ◂— 0x38 /* '8' */
07:0038│     0x7fffffff7e68 ◂— 0x4
[ BACKTRACE ]
 ► f 0   0x7ffff754da2f unlink_chunk.isra+15
   f 1   0x7ffff7550773 _int_malloc+2947
   f 2   0x7ffff75522d4 malloc+116
   f 3   0x7ffff78c17d2 co64_box_new+18
   f 4   0x7ffff78f8aa9 gf_isom_box_new+153
   f 5   0x7ffff791009c shift_chunk_offsets.part+284
   f 6   0x7ffff79103a7 inplace_shift_moov_meta_offsets+231
   f 7   0x7ffff7910e3c inplace_shift_mdat+732

```
untrusted pointer dereference in unlink_chunk.isra
This is a GitHub Issue
repo:gpac
owner:gpac
Title : untrusted pointer dereference in unlink_chunk.isra
Issue date:

--- start body ---
Thanks for reporting your issue. Please make sure these boxes are checked before submitting your issue - thank you!

- [Yes ] I looked for a similar issue and couldn't find any.
- [ Yes] I tried with the latest version of GPAC. Installers available at http://gpac.io/downloads/gpac-nightly-builds/
- [ Yes] I give enough information for contributors to reproduce my issue (meaningful title, github labels, platform and compiler, command-line ...). I can share files anonymously with this dropbox: https://www.mediafire.com/filedrop/filedrop_hosted.php?drop=eec9e058a9486fe4e99c33021481d9e1826ca9dbc242a6cfaab0fe95da5e5d95

Detailed guidelines: http://gpac.io/2013/07/16/how-to-file-a-bug-properly/

**Version:**
```
./MP4Box -version
```

**command:**
```
./bin/gcc/MP4Box -hint POC2
```
[POC2.zip](https://github.com/gpac/gpac/files/7763677/POC2.zip)

**Result**
```
segmentation fault
```
**bt**

```
Program received signal SIGSEGV, Segmentation fault.
0x00007ffff754da2f in unlink_chunk (p=p@entry=0x5555555e1480, av=0x7ffff76a0b80 <main_arena>) at malloc.c:1453
1453	malloc.c: No such file or directory.
LEGEND: STACK | HEAP | CODE | DATA | RWX | RODATA
[ REGISTERS ]
 RAX  0x14000007a0
 RBX  0x7ffff76a0b80 (main_arena) ◂— 0x0
 RCX  0x14000007a5
 RDX  0x7ffff76a10b0 (main_arena+1328) —▸ 0x7ffff76a10a0 (main_arena+1312) —▸ 0x7ffff76a1090 (main_arena+1296) —▸ 0x7ffff76a1080 (main_arena+1280) —▸ 0x7ffff76a1070 (main_arena+1264) ◂— ...
 RDI  0x5555555e1480 ◂— 0x8013f76a1f74
 RSI  0x4000
 R8   0x7ffff76a0c10 (main_arena+144) —▸ 0x7ffff76a0c00 (main_arena+128) —▸ 0x5555555e0f10 ◂— 0x1400000014
 R9   0x0
 R10  0x7ffff7e0e94e ◂— ' but no data reference entry found\n'
 R11  0x7ffff76a0be0 (main_arena+96) —▸ 0x5555555e69e0 ◂— 0x0
 R12  0x1400000760
 R13  0x40
 R14  0x14000007a0
 R15  0x2
 RBP  0x38
 RSP  0x7fffffff7e30 —▸ 0x5555555e2a00 ◂— 0x1473746383
 RIP  0x7ffff754da2f (unlink_chunk.isra+15) ◂— cmp    rax, qword ptr [rdi + rax]
[ DISASM ]
 ► 0x7ffff754da2f <unlink_chunk.isra+15>     cmp    rax, qword ptr [rdi + rax]
   0x7ffff754da33 <unlink_chunk.isra+19>     jne    unlink_chunk.isra+191                <unlink_chunk.isra+191>
    ↓
   0x7ffff754dadf <unlink_chunk.isra+191>    lea    rdi, [rip + 0x11f954]
   0x7ffff754dae6 <unlink_chunk.isra+198>    call   malloc_printerr                <malloc_printerr>
 
   0x7ffff754daeb <unlink_chunk.isra+203>    lea    rdi, [rip + 0x123756]
   0x7ffff754daf2 <unlink_chunk.isra+210>    call   malloc_printerr                <malloc_printerr>
 
   0x7ffff754daf7                            nop    word ptr [rax + rax]
   0x7ffff754db00 <malloc_consolidate>       push   r15
   0x7ffff754db02 <malloc_consolidate+2>     lea    rax, [rdi + 0x60]
   0x7ffff754db06 <malloc_consolidate+6>     mov    r15, rdi
   0x7ffff754db09 <malloc_consolidate+9>     push   r14
[ STACK ]
00:0000│ rsp 0x7fffffff7e30 —▸ 0x5555555e2a00 ◂— 0x1473746383
01:0008│     0x7fffffff7e38 —▸ 0x7ffff7550773 (_int_malloc+2947) ◂— cmp    r12, 0x1f
02:0010│     0x7fffffff7e40 —▸ 0x5555555e1480 ◂— 0x8013f76a1f74
03:0018│     0x7fffffff7e48 —▸ 0x7ffff76a0be0 (main_arena+96) —▸ 0x5555555e69e0 ◂— 0x0
04:0020│     0x7fffffff7e50 —▸ 0x7fffffff7e60 ◂— 0x38 /* '8' */
05:0028│     0x7fffffff7e58 ◂— 0xdab84f8dc31ec400
06:0030│     0x7fffffff7e60 ◂— 0x38 /* '8' */
07:0038│     0x7fffffff7e68 ◂— 0x4
[ BACKTRACE ]
 ► f 0   0x7ffff754da2f unlink_chunk.isra+15
   f 1   0x7ffff7550773 _int_malloc+2947
   f 2   0x7ffff75522d4 malloc+116
   f 3   0x7ffff78c17d2 co64_box_new+18
   f 4   0x7ffff78f8aa9 gf_isom_box_new+153
   f 5   0x7ffff791009c shift_chunk_offsets.part+284
   f 6   0x7ffff79103a7 inplace_shift_moov_meta_offsets+231
   f 7   0x7ffff7910e3c inplace_shift_mdat+732

```
--- end body ---
