A Pointer Dereference Vulnerability exists in GPAC 1.0.1 via the _fseeko function, which causes a Denial of Service.
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
MP4Box - GPAC version 1.1.0-DEV-rev1574-g8b22f0912-master
(c) 2000-2021 Telecom Paris distributed under LGPL v2.1+ - http://gpac.io

Please cite our work in your research:
	GPAC Filters: https://doi.org/10.1145/3339825.3394929
	GPAC: https://doi.org/10.1145/1291233.1291452

GPAC Configuration: 
Features: GPAC_CONFIG_LINUX GPAC_64_BITS GPAC_HAS_IPV6 GPAC_HAS_SSL GPAC_HAS_SOCK_UN GPAC_MINIMAL_ODF GPAC_HAS_QJS GPAC_HAS_JPEG GPAC_HAS_PNG GPAC_HAS_LINUX_DVB
```


**command:**
```
./bin/gcc/MP4Box -hint POC4

```
[POC4.zip](https://github.com/gpac/gpac/files/7763835/POC4.zip)

**Result**
```
 Segmentation fault.
```
**bt**

```
Program received signal SIGSEGV, Segmentation fault.
0x00007ffff7544911 in __fseeko (fp=0x5555555e1510, offset=2560, whence=0) at fseeko.c:39
39	fseeko.c: No such file or directory.
LEGEND: STACK | HEAP | CODE | DATA | RWX | RODATA
───────────────────────────────────────────────────────────────────────[ REGISTERS ]────────────────────────────────────────────────────────────────────────
 RAX  0x0
 RBX  0x5555555e1510 ◂— 0x8013fbad2494
 RCX  0x0
 RDX  0x0
 RDI  0x5569555e1604
 RSI  0xa00
 R8   0x5555555e0f70 ◂— 0x1400000014
 R9   0x7fffffff7f00 —▸ 0x7ffff76a15c0 (_IO_2_1_stderr_) ◂— 0xfbad2887
 R10  0x7ffff76d927a ◂— 'gf_isom_box_size'
 R11  0x7ffff78fa0d0 (gf_isom_box_size) ◂— endbr64 
 R12  0x0
 R13  0x7ffff697e740 ◂— 0x7ffff697e740
 R14  0x7fffffff84e0 ◂— 0x0
 R15  0x7fffffff8040 ◂— 0x15f
 RBP  0xa00
 RSP  0x7fffffff7fd0 ◂— 0x0
 RIP  0x7ffff7544911 (fseeko64+49) ◂— cmp    qword ptr [rdi + 8], r13
[ DISASM ]
 ► 0x7ffff7544911 <fseeko64+49>     cmp    qword ptr [rdi + 8], r13
   0x7ffff7544915 <fseeko64+53>     je     fseeko64+86                <fseeko64+86>
    ↓
   0x7ffff7544936 <fseeko64+86>     add    dword ptr [rdi + 4], 1
   0x7ffff754493a <fseeko64+90>     mov    ecx, 3
   0x7ffff754493f <fseeko64+95>     mov    edx, r12d
   0x7ffff7544942 <fseeko64+98>     mov    rsi, rbp
   0x7ffff7544945 <fseeko64+101>    mov    rdi, rbx
   0x7ffff7544948 <fseeko64+104>    call   _IO_seekoff_unlocked                <_IO_seekoff_unlocked>
 
   0x7ffff754494d <fseeko64+109>    xor    r8d, r8d
   0x7ffff7544950 <fseeko64+112>    cmp    rax, -1
   0x7ffff7544954 <fseeko64+116>    sete   r8b
[ STACK ]
00:0000│ rsp 0x7fffffff7fd0 ◂— 0x0
01:0008│     0x7fffffff7fd8 —▸ 0x5555555df7a0 —▸ 0x5555555e1510 ◂— 0x8013fbad2494
02:0010│     0x7fffffff7fe0 ◂— 0xa00
03:0018│     0x7fffffff7fe8 ◂— 0x0
04:0020│     0x7fffffff7ff0 —▸ 0x7fffffff84d8 ◂— 0x14
05:0028│     0x7fffffff7ff8 —▸ 0x7ffff77767f4 (gf_bs_seek+452) ◂— mov    qword ptr [rbx + 0x18], rbp
06:0030│     0x7fffffff8000 —▸ 0x5555555da950 ◂— 0x0
07:0038│     0x7fffffff8008 —▸ 0x5555555df7a0 —▸ 0x5555555e1510 ◂— 0x8013fbad2494
[ BACKTRACE ]
 ► f 0   0x7ffff7544911 fseeko64+49
   f 1   0x7ffff77767f4 gf_bs_seek+452
   f 2   0x7ffff7910c98 inplace_shift_mdat+312
   f 3   0x7ffff7915009 WriteToFile+2713
   f 4   0x7ffff7906432 gf_isom_write+370
   f 5   0x7ffff79064b8 gf_isom_close+24
   f 6   0x55555557bd12 mp4boxMain+7410
   f 7   0x7ffff74dc0b3 __libc_start_main+243
───────────────────────────────────────────────

```
Untrusted pointer dereference in __fseeko()
This is a GitHub Issue
repo:gpac
owner:gpac
Title : Untrusted pointer dereference in __fseeko()
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
MP4Box - GPAC version 1.1.0-DEV-rev1574-g8b22f0912-master
(c) 2000-2021 Telecom Paris distributed under LGPL v2.1+ - http://gpac.io

Please cite our work in your research:
	GPAC Filters: https://doi.org/10.1145/3339825.3394929
	GPAC: https://doi.org/10.1145/1291233.1291452

GPAC Configuration: 
Features: GPAC_CONFIG_LINUX GPAC_64_BITS GPAC_HAS_IPV6 GPAC_HAS_SSL GPAC_HAS_SOCK_UN GPAC_MINIMAL_ODF GPAC_HAS_QJS GPAC_HAS_JPEG GPAC_HAS_PNG GPAC_HAS_LINUX_DVB
```


**command:**
```
./bin/gcc/MP4Box -hint POC4

```
[POC4.zip](https://github.com/gpac/gpac/files/7763835/POC4.zip)

**Result**
```
 Segmentation fault.
```
**bt**

```
Program received signal SIGSEGV, Segmentation fault.
0x00007ffff7544911 in __fseeko (fp=0x5555555e1510, offset=2560, whence=0) at fseeko.c:39
39	fseeko.c: No such file or directory.
LEGEND: STACK | HEAP | CODE | DATA | RWX | RODATA
───────────────────────────────────────────────────────────────────────[ REGISTERS ]────────────────────────────────────────────────────────────────────────
 RAX  0x0
 RBX  0x5555555e1510 ◂— 0x8013fbad2494
 RCX  0x0
 RDX  0x0
 RDI  0x5569555e1604
 RSI  0xa00
 R8   0x5555555e0f70 ◂— 0x1400000014
 R9   0x7fffffff7f00 —▸ 0x7ffff76a15c0 (_IO_2_1_stderr_) ◂— 0xfbad2887
 R10  0x7ffff76d927a ◂— 'gf_isom_box_size'
 R11  0x7ffff78fa0d0 (gf_isom_box_size) ◂— endbr64 
 R12  0x0
 R13  0x7ffff697e740 ◂— 0x7ffff697e740
 R14  0x7fffffff84e0 ◂— 0x0
 R15  0x7fffffff8040 ◂— 0x15f
 RBP  0xa00
 RSP  0x7fffffff7fd0 ◂— 0x0
 RIP  0x7ffff7544911 (fseeko64+49) ◂— cmp    qword ptr [rdi + 8], r13
[ DISASM ]
 ► 0x7ffff7544911 <fseeko64+49>     cmp    qword ptr [rdi + 8], r13
   0x7ffff7544915 <fseeko64+53>     je     fseeko64+86                <fseeko64+86>
    ↓
   0x7ffff7544936 <fseeko64+86>     add    dword ptr [rdi + 4], 1
   0x7ffff754493a <fseeko64+90>     mov    ecx, 3
   0x7ffff754493f <fseeko64+95>     mov    edx, r12d
   0x7ffff7544942 <fseeko64+98>     mov    rsi, rbp
   0x7ffff7544945 <fseeko64+101>    mov    rdi, rbx
   0x7ffff7544948 <fseeko64+104>    call   _IO_seekoff_unlocked                <_IO_seekoff_unlocked>
 
   0x7ffff754494d <fseeko64+109>    xor    r8d, r8d
   0x7ffff7544950 <fseeko64+112>    cmp    rax, -1
   0x7ffff7544954 <fseeko64+116>    sete   r8b
[ STACK ]
00:0000│ rsp 0x7fffffff7fd0 ◂— 0x0
01:0008│     0x7fffffff7fd8 —▸ 0x5555555df7a0 —▸ 0x5555555e1510 ◂— 0x8013fbad2494
02:0010│     0x7fffffff7fe0 ◂— 0xa00
03:0018│     0x7fffffff7fe8 ◂— 0x0
04:0020│     0x7fffffff7ff0 —▸ 0x7fffffff84d8 ◂— 0x14
05:0028│     0x7fffffff7ff8 —▸ 0x7ffff77767f4 (gf_bs_seek+452) ◂— mov    qword ptr [rbx + 0x18], rbp
06:0030│     0x7fffffff8000 —▸ 0x5555555da950 ◂— 0x0
07:0038│     0x7fffffff8008 —▸ 0x5555555df7a0 —▸ 0x5555555e1510 ◂— 0x8013fbad2494
[ BACKTRACE ]
 ► f 0   0x7ffff7544911 fseeko64+49
   f 1   0x7ffff77767f4 gf_bs_seek+452
   f 2   0x7ffff7910c98 inplace_shift_mdat+312
   f 3   0x7ffff7915009 WriteToFile+2713
   f 4   0x7ffff7906432 gf_isom_write+370
   f 5   0x7ffff79064b8 gf_isom_close+24
   f 6   0x55555557bd12 mp4boxMain+7410
   f 7   0x7ffff74dc0b3 __libc_start_main+243
───────────────────────────────────────────────

```
--- end body ---
