aacplusenc: NULL pointer dereference in DeleteBitBuffer (bitbuffer.c)

Description:
aacplusenc is an High-Efficiency AAC (AAC+) Encoder.

The complete ASan output of the issue:

# aacplusenc $FILE out.aac 32
                                                                                                                                                                                                                  
*************************************************************                                                                                                                                                     
* Enhanced aacPlus Encoder                                                                                                                                                                                        
* Build Aug 30 2017, 14:40:49                                                                                                                                                                                     
* Matteo Croce                                                                                                                                                                                
*************************************************************                                                                                                                                                     
                                                                                                                                                                                                                  
input file 101.crashes.wav:                                                                                                                                                                                       
sr = 48000, nc = 1                                                                                                                                                                                                
                                                                                                                                                                                                                  
output file out.aac:                                                                                                                                                                                              
br = 32000 sr-OUT = 48000  nc-OUT = 1                                                                                                                                                                             
                                                                                                                                                                                                                  
                                                                                                                                                                                                                  
ASAN:DEADLYSIGNAL
=================================================================
==21496==ERROR: AddressSanitizer: SEGV on unknown address 0x000000000030 (pc 0x000000562e2f bp 0x7ffc2ec32430 sp 0x7ffc2ec32430 T0)
==21496==The signal is caused by a WRITE memory access.
==21496==Hint: address points to the zero page.
    #0 0x562e2e in DeleteBitBuffer /var/tmp/portage/media-sound/aacplusenc-0.17.5/work/aacplusenc/libbitbuf/bitbuffer.c:97:23
    #1 0x50d909 in AacEncClose /var/tmp/portage/media-sound/aacplusenc-0.17.5/work/aacplusenc/libaacenc/aacenc.c:469:5
    #2 0x50c0df in main /var/tmp/portage/media-sound/aacplusenc-0.17.5/work/aacplusenc/aacplusenc.c:536:2
    #3 0x7f0e4c21b680 in __libc_start_main /var/tmp/portage/sys-libs/glibc-2.23-r4/work/glibc-2.23/csu/../csu/libc-start.c:289
    #4 0x419e78 in _init (/usr/bin/aacplusenc+0x419e78)

AddressSanitizer can not provide additional info.
SUMMARY: AddressSanitizer: SEGV /var/tmp/portage/media-sound/aacplusenc-0.17.5/work/aacplusenc/libbitbuf/bitbuffer.c:97:23 in DeleteBitBuffer
==21496==ABORTING

Affected version:
0.17.5

Fixed version:
N/A

Commit fix:
N/A

Credit:
This bug was discovered by Agostino Sarubbo of Gentoo.

CVE:
CVE-2017-14181

Reproducer:
https://github.com/asarubbo/poc/blob/master/00332-aacplusenc-NULLptr-DeleteBitBuffer

Timeline:
2017-08-31: bug discovered and reported to upstream
2017-09-07: blog post about the issue
2017-09-07: CVE assigned

Note:
This bug was found with American Fuzzy Lop.
This bug was identified with bare metal servers donated by Packet. This work is also supported by the Core Infrastructure Initiative.

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aacplusenc: NULL pointer dereference in DeleteBitBuffer (bitbuffer.c)

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