An issue was discovered in gpac 0.8.0. The stbl_GetSampleSize function in isomedia/stbl_read.c has a heap-based buffer overflow which can lead to a denial of service (DOS) via a crafted media file.
- [ y] I looked for a similar issue and couldn't find any.
- [ y] I tried with the latest version of GPAC. Installers available at http://gpac.io/downloads/gpac-nightly-builds/
- [ y] 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

**Describe the bug**
A heap-based buffer overflow was discovered in libgpac, during structure GF_SampleSizeBox 'stsz' member 'sizes' points to an invalid address. The issue is being triggered in the function stbl_GetSampleSize() at isomedia/stbl_read.c

**To Reproduce**
Steps to reproduce the behavior:
1. Compile according to the default configuration
```bash
$ CC="gcc -fsanitize=address -g" CXX="g++ -fsanitize=address -g" ./configure --static-mp4box
$ make
```

2. execute command
```bash
MP4Box -hint $poc
```
[poc](https://github.com/14isnot40/vul_discovery/blob/master/stbl_GetSampleSize_hbo) can be found here.

**Expected behavior**
An attacker can exploit this vulnerability by submitting a malicious media file that exploits this issue. This will result in a Denial of Service (DoS) and potentially Information Exposure when the application attempts to process the file.

**Screenshots**
ASAN Reports
```bash
==94786==ERROR: AddressSanitizer: heap-buffer-overflow on address 0x61400000fdd0 at pc 0x000000744231 bp 0x7fffffff83c0 sp 0x7fffffff83b0
READ of size 4 at 0x61400000fdd0 thread T0
    #0 0x744230 in stbl_GetSampleSize isomedia/stbl_read.c:135
    #1 0x717f3d in Media_GetSample isomedia/media.c:418
    #2 0x6cd966 in gf_isom_get_sample_info isomedia/isom_read.c:1692
    #3 0x912ed8 in gf_media_get_sample_average_infos media_tools/isom_hinter.c:54
    #4 0x913d43 in gf_hinter_track_new media_tools/isom_hinter.c:560
    #5 0x41e02e in HintFile (/usr/local/bin/MP4Box+0x41e02e)
    #6 0x429806 in mp4boxMain (/usr/local/bin/MP4Box+0x429806)
    #7 0x7ffff615e82f in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x2082f)
    #8 0x41d668 in _start (/usr/local/bin/MP4Box+0x41d668)

0x61400000fdd0 is located 0 bytes to the right of 400-byte region [0x61400000fc40,0x61400000fdd0)
allocated by thread T0 here:
    #0 0x7ffff6f02961 in realloc (/usr/lib/x86_64-linux-gnu/libasan.so.2+0x98961)
    #1 0x7516dd in stbl_AppendSize isomedia/stbl_write.c:1487

SUMMARY: AddressSanitizer: heap-buffer-overflow isomedia/stbl_read.c:135 stbl_GetSampleSize
Shadow bytes around the buggy address:
  0x0c287fff9f60: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c287fff9f70: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c287fff9f80: fa fa fa fa fa fa fa fa 00 00 00 00 00 00 00 00
  0x0c287fff9f90: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x0c287fff9fa0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
=>0x0c287fff9fb0: 00 00 00 00 00 00 00 00 00 00[fa]fa fa fa fa fa
  0x0c287fff9fc0: fa fa fa fa fa fa fa fa fd fd fd fd fd fd fd fd
  0x0c287fff9fd0: fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd
  0x0c287fff9fe0: fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd
  0x0c287fff9ff0: fd fd fd fd fd fd fd fd fd fd fd fd fa fa fa fa
  0x0c287fffa000: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
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
==94786==ABORTING
```
Possible causes of vulnerabilities
structure GF_SampleSizeBox 'stsz' member 'sizes' points to an invalid address
```cpp
GF_Err stbl_GetSampleSize(GF_SampleSizeBox *stsz, u32 SampleNumber, u32 *Size)
{
	if (!stsz || !SampleNumber || SampleNumber > stsz->sampleCount) return GF_BAD_PARAM;

	(*Size) = 0;

	if (stsz->sampleSize && (stsz->type != GF_ISOM_BOX_TYPE_STZ2)) {
		(*Size) = stsz->sampleSize;
	} else if (stsz->sizes) {
		(*Size) = stsz->sizes[SampleNumber - 1];
	}
	return GF_OK;
}
```

**System (please complete the following information):**
 - OS version : Ubuntu 16.04
 - GPAC Version : GPAC 0.8.0-e10d39d-master branch
Heap-buffer-overflow isomedia/stbl_read.c:135 in stbl_GetSampleSize()
This is a GitHub Issue
repo:gpac
owner:gpac
Title : Heap-buffer-overflow isomedia/stbl_read.c:135 in stbl_GetSampleSize()
Issue date:

--- start body ---
- [ y] I looked for a similar issue and couldn't find any.
- [ y] I tried with the latest version of GPAC. Installers available at http://gpac.io/downloads/gpac-nightly-builds/
- [ y] 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

**Describe the bug**
A heap-based buffer overflow was discovered in libgpac, during structure GF_SampleSizeBox 'stsz' member 'sizes' points to an invalid address. The issue is being triggered in the function stbl_GetSampleSize() at isomedia/stbl_read.c

**To Reproduce**
Steps to reproduce the behavior:
1. Compile according to the default configuration
```bash
$ CC="gcc -fsanitize=address -g" CXX="g++ -fsanitize=address -g" ./configure --static-mp4box
$ make
```

2. execute command
```bash
MP4Box -hint $poc
```
[poc](https://github.com/14isnot40/vul_discovery/blob/master/stbl_GetSampleSize_hbo) can be found here.

**Expected behavior**
An attacker can exploit this vulnerability by submitting a malicious media file that exploits this issue. This will result in a Denial of Service (DoS) and potentially Information Exposure when the application attempts to process the file.

**Screenshots**
ASAN Reports
```bash
==94786==ERROR: AddressSanitizer: heap-buffer-overflow on address 0x61400000fdd0 at pc 0x000000744231 bp 0x7fffffff83c0 sp 0x7fffffff83b0
READ of size 4 at 0x61400000fdd0 thread T0
    #0 0x744230 in stbl_GetSampleSize isomedia/stbl_read.c:135
    #1 0x717f3d in Media_GetSample isomedia/media.c:418
    #2 0x6cd966 in gf_isom_get_sample_info isomedia/isom_read.c:1692
    #3 0x912ed8 in gf_media_get_sample_average_infos media_tools/isom_hinter.c:54
    #4 0x913d43 in gf_hinter_track_new media_tools/isom_hinter.c:560
    #5 0x41e02e in HintFile (/usr/local/bin/MP4Box+0x41e02e)
    #6 0x429806 in mp4boxMain (/usr/local/bin/MP4Box+0x429806)
    #7 0x7ffff615e82f in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x2082f)
    #8 0x41d668 in _start (/usr/local/bin/MP4Box+0x41d668)

0x61400000fdd0 is located 0 bytes to the right of 400-byte region [0x61400000fc40,0x61400000fdd0)
allocated by thread T0 here:
    #0 0x7ffff6f02961 in realloc (/usr/lib/x86_64-linux-gnu/libasan.so.2+0x98961)
    #1 0x7516dd in stbl_AppendSize isomedia/stbl_write.c:1487

SUMMARY: AddressSanitizer: heap-buffer-overflow isomedia/stbl_read.c:135 stbl_GetSampleSize
Shadow bytes around the buggy address:
  0x0c287fff9f60: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c287fff9f70: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c287fff9f80: fa fa fa fa fa fa fa fa 00 00 00 00 00 00 00 00
  0x0c287fff9f90: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x0c287fff9fa0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
=>0x0c287fff9fb0: 00 00 00 00 00 00 00 00 00 00[fa]fa fa fa fa fa
  0x0c287fff9fc0: fa fa fa fa fa fa fa fa fd fd fd fd fd fd fd fd
  0x0c287fff9fd0: fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd
  0x0c287fff9fe0: fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd
  0x0c287fff9ff0: fd fd fd fd fd fd fd fd fd fd fd fd fa fa fa fa
  0x0c287fffa000: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
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
==94786==ABORTING
```
Possible causes of vulnerabilities
structure GF_SampleSizeBox 'stsz' member 'sizes' points to an invalid address
```cpp
GF_Err stbl_GetSampleSize(GF_SampleSizeBox *stsz, u32 SampleNumber, u32 *Size)
{
	if (!stsz || !SampleNumber || SampleNumber > stsz->sampleCount) return GF_BAD_PARAM;

	(*Size) = 0;

	if (stsz->sampleSize && (stsz->type != GF_ISOM_BOX_TYPE_STZ2)) {
		(*Size) = stsz->sampleSize;
	} else if (stsz->sizes) {
		(*Size) = stsz->sizes[SampleNumber - 1];
	}
	return GF_OK;
}
```

**System (please complete the following information):**
 - OS version : Ubuntu 16.04
 - GPAC Version : GPAC 0.8.0-e10d39d-master branch
--- end body ---
