GPAC 2.0 allows a heap-based buffer overflow in gf_base64_encode. It can be triggered via MP4Box.
Thanks for reporting your issue. Please make sure these boxes are checked before submitting your issue - thank you!

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

***Describe the bug***
There is a heap-buffer-overflow bug, which can be triggered via MP4Box+ ASan

***To Reproduce***
Steps to reproduce the behavior:
```
./configure --cc=clang --cxx=clang++ --enable-sanitizer
make -j$(nproc)
./bin/gcc/MP4Box -diso POC
```

Output:
```
[iso file] Box "moof" (start 0) has 3 extra bytes
[iso file] Movie fragment but no moov (yet) - possibly broken parsing!
[iso file] Box "moof" (start 23) has 3 extra bytes
[iso file] Box "moof" (start 34) has 3 extra bytes
[iso file] Box "moof" (start 77) has 3 extra bytes
[iso file] Box "tref" (start 45) has 4 extra bytes
[iso file] Unknown top-level box type 0005hEB
=================================================================
==1787100==ERROR: AddressSanitizer: heap-buffer-overflow on address 0x602000001012 at pc 0x0000005b4fdc bp 0x7ffde5e08a70 sp 0x7ffde5e08a68
WRITE of size 1 at 0x602000001012 thread T0
    #0 0x5b4fdb in gf_base64_encode /home/hzheng/workspace/benchmarks/reproduce/gpac/src/utils/base_encoding.c:48:13
    #1 0x8fdb6b in colr_box_dump /home/hzheng/workspace/benchmarks/reproduce/gpac/src/isomedia/box_dump.c:5493:15
    #2 0x90c095 in gf_isom_box_dump /home/hzheng/workspace/benchmarks/reproduce/gpac/src/isomedia/box_funcs.c:2076:2
    #3 0x8cf29c in gf_isom_dump /home/hzheng/workspace/benchmarks/reproduce/gpac/src/isomedia/box_dump.c:135:3
    #4 0x539be2 in dump_isom_xml /home/hzheng/workspace/benchmarks/reproduce/gpac/applications/mp4box/filedump.c:1954:6
    #5 0x51939b in mp4boxMain /home/hzheng/workspace/benchmarks/reproduce/gpac/applications/mp4box/main.c:6155:7
    #6 0x7faccbbfc0b2 in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x270b2)
    #7 0x41fdad in _start (/home/hzheng/workspace/benchmarks/reproduce/gpac/bin/gcc/MP4Box+0x41fdad)

0x602000001012 is located 0 bytes to the right of 2-byte region [0x602000001010,0x602000001012)
allocated by thread T0 here:
    #0 0x4c58ff in malloc /home/hzheng/env/llvm-project/compiler-rt/lib/asan/asan_malloc_linux.cpp:145:3
    #1 0x8fdb37 in gf_malloc /home/hzheng/workspace/benchmarks/reproduce/gpac/src/utils/alloc.c:150:9
    #2 0x8fdb37 in colr_box_dump /home/hzheng/workspace/benchmarks/reproduce/gpac/src/isomedia/box_dump.c:5492:20
    #3 0x90c095 in gf_isom_box_dump /home/hzheng/workspace/benchmarks/reproduce/gpac/src/isomedia/box_funcs.c:2076:2
    #4 0x8cf29c in gf_isom_dump /home/hzheng/workspace/benchmarks/reproduce/gpac/src/isomedia/box_dump.c:135:3
    #5 0x539be2 in dump_isom_xml /home/hzheng/workspace/benchmarks/reproduce/gpac/applications/mp4box/filedump.c:1954:6
    #6 0x51939b in mp4boxMain /home/hzheng/workspace/benchmarks/reproduce/gpac/applications/mp4box/main.c:6155:7
    #7 0x7faccbbfc0b2 in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x270b2)

SUMMARY: AddressSanitizer: heap-buffer-overflow /home/hzheng/workspace/benchmarks/reproduce/gpac/src/utils/base_encoding.c:48:13 in gf_base64_encode
Shadow bytes around the buggy address:
  0x0c047fff81b0: fa fa 07 fa fa fa fd fa fa fa 04 fa fa fa 00 02
  0x0c047fff81c0: fa fa fd fa fa fa 00 07 fa fa 00 00 fa fa 00 00
  0x0c047fff81d0: fa fa 00 fa fa fa fd fa fa fa 00 04 fa fa 00 00
  0x0c047fff81e0: fa fa 00 00 fa fa 01 fa fa fa 00 00 fa fa 00 00
  0x0c047fff81f0: fa fa 04 fa fa fa 00 00 fa fa 04 fa fa fa 01 fa
=>0x0c047fff8200: fa fa[02]fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c047fff8210: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c047fff8220: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c047fff8230: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c047fff8240: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c047fff8250: 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
  Freed heap region:       fd
  Stack left redzone:      f1
  Stack mid redzone:       f2
  Stack right redzone:     f3
  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
  Shadow gap:              cc
==1787100==ABORTING
```

***Environment***
gpac commit 54e9ed807fd24d83aa051fb097466d8760225401
clang release/12.x
ubuntu 20.04

***POC***
[POC.zip](https://github.com/gpac/gpac/files/8222176/POC.zip)

***Credit***
Han Zheng
[NCNIPC of China](http://www.nipc.org.cn)
[Hexhive](http://hexhive.epfl.ch/)
[BUG] heap-buffer-overflow in gf_base64_encode
This is a GitHub Issue
repo:gpac
owner:gpac
Title : [BUG] heap-buffer-overflow in gf_base64_encode
Issue date:

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

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

***Describe the bug***
There is a heap-buffer-overflow bug, which can be triggered via MP4Box+ ASan

***To Reproduce***
Steps to reproduce the behavior:
```
./configure --cc=clang --cxx=clang++ --enable-sanitizer
make -j$(nproc)
./bin/gcc/MP4Box -diso POC
```

Output:
```
[iso file] Box "moof" (start 0) has 3 extra bytes
[iso file] Movie fragment but no moov (yet) - possibly broken parsing!
[iso file] Box "moof" (start 23) has 3 extra bytes
[iso file] Box "moof" (start 34) has 3 extra bytes
[iso file] Box "moof" (start 77) has 3 extra bytes
[iso file] Box "tref" (start 45) has 4 extra bytes
[iso file] Unknown top-level box type 0005hEB
=================================================================
==1787100==ERROR: AddressSanitizer: heap-buffer-overflow on address 0x602000001012 at pc 0x0000005b4fdc bp 0x7ffde5e08a70 sp 0x7ffde5e08a68
WRITE of size 1 at 0x602000001012 thread T0
    #0 0x5b4fdb in gf_base64_encode /home/hzheng/workspace/benchmarks/reproduce/gpac/src/utils/base_encoding.c:48:13
    #1 0x8fdb6b in colr_box_dump /home/hzheng/workspace/benchmarks/reproduce/gpac/src/isomedia/box_dump.c:5493:15
    #2 0x90c095 in gf_isom_box_dump /home/hzheng/workspace/benchmarks/reproduce/gpac/src/isomedia/box_funcs.c:2076:2
    #3 0x8cf29c in gf_isom_dump /home/hzheng/workspace/benchmarks/reproduce/gpac/src/isomedia/box_dump.c:135:3
    #4 0x539be2 in dump_isom_xml /home/hzheng/workspace/benchmarks/reproduce/gpac/applications/mp4box/filedump.c:1954:6
    #5 0x51939b in mp4boxMain /home/hzheng/workspace/benchmarks/reproduce/gpac/applications/mp4box/main.c:6155:7
    #6 0x7faccbbfc0b2 in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x270b2)
    #7 0x41fdad in _start (/home/hzheng/workspace/benchmarks/reproduce/gpac/bin/gcc/MP4Box+0x41fdad)

0x602000001012 is located 0 bytes to the right of 2-byte region [0x602000001010,0x602000001012)
allocated by thread T0 here:
    #0 0x4c58ff in malloc /home/hzheng/env/llvm-project/compiler-rt/lib/asan/asan_malloc_linux.cpp:145:3
    #1 0x8fdb37 in gf_malloc /home/hzheng/workspace/benchmarks/reproduce/gpac/src/utils/alloc.c:150:9
    #2 0x8fdb37 in colr_box_dump /home/hzheng/workspace/benchmarks/reproduce/gpac/src/isomedia/box_dump.c:5492:20
    #3 0x90c095 in gf_isom_box_dump /home/hzheng/workspace/benchmarks/reproduce/gpac/src/isomedia/box_funcs.c:2076:2
    #4 0x8cf29c in gf_isom_dump /home/hzheng/workspace/benchmarks/reproduce/gpac/src/isomedia/box_dump.c:135:3
    #5 0x539be2 in dump_isom_xml /home/hzheng/workspace/benchmarks/reproduce/gpac/applications/mp4box/filedump.c:1954:6
    #6 0x51939b in mp4boxMain /home/hzheng/workspace/benchmarks/reproduce/gpac/applications/mp4box/main.c:6155:7
    #7 0x7faccbbfc0b2 in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x270b2)

SUMMARY: AddressSanitizer: heap-buffer-overflow /home/hzheng/workspace/benchmarks/reproduce/gpac/src/utils/base_encoding.c:48:13 in gf_base64_encode
Shadow bytes around the buggy address:
  0x0c047fff81b0: fa fa 07 fa fa fa fd fa fa fa 04 fa fa fa 00 02
  0x0c047fff81c0: fa fa fd fa fa fa 00 07 fa fa 00 00 fa fa 00 00
  0x0c047fff81d0: fa fa 00 fa fa fa fd fa fa fa 00 04 fa fa 00 00
  0x0c047fff81e0: fa fa 00 00 fa fa 01 fa fa fa 00 00 fa fa 00 00
  0x0c047fff81f0: fa fa 04 fa fa fa 00 00 fa fa 04 fa fa fa 01 fa
=>0x0c047fff8200: fa fa[02]fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c047fff8210: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c047fff8220: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c047fff8230: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c047fff8240: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c047fff8250: 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
  Freed heap region:       fd
  Stack left redzone:      f1
  Stack mid redzone:       f2
  Stack right redzone:     f3
  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
  Shadow gap:              cc
==1787100==ABORTING
```

***Environment***
gpac commit 54e9ed807fd24d83aa051fb097466d8760225401
clang release/12.x
ubuntu 20.04

***POC***
[POC.zip](https://github.com/gpac/gpac/files/8222176/POC.zip)

***Credit***
Han Zheng
[NCNIPC of China](http://www.nipc.org.cn)
[Hexhive](http://hexhive.epfl.ch/)
--- end body ---
