A null pointer dereference issue exists in GNU LibreDWG 0.10.2641 via htmlescape ../../programs/escape.c:29. which causes a denial of service (application crash).
Hi,
After fuzzing libredwg, I found the following bugs on the latest commit on master.
Command: ./dwg2SVG $PoC
**1.NULL pointer dereference in htmlescape ../../programs/escape.c:29**
POC: https://github.com/linhlhq/research/blob/master/PoCs/libreDWG_7b9cb829/id:000013%2Csig:06%2Csrc:000000%2Cop:flip1%2Cpos:46417
ASAN says:
```
=================================================================
==19607==ERROR: AddressSanitizer: SEGV on unknown address 0x000000000000 (pc 0x7f433bb56646 bp 0x7ffed1176670 sp 0x7ffed1175de8 T0)
==19607==The signal is caused by a READ memory access.
==19607==Hint: address points to the zero page.
    #0 0x7f433bb56645  (/lib/x86_64-linux-gnu/libc.so.6+0xb1645)
    #1 0x7f433c28557b  (/usr/lib/x86_64-linux-gnu/libasan.so.4+0x5157b)
    #2 0x55950b27cdd4 in htmlescape ../../programs/escape.c:29
    #3 0x55950b27abb5 in output_TEXT ../../programs/dwg2SVG.c:113
    #4 0x55950b27abb5 in output_object ../../programs/dwg2SVG.c:312
    #5 0x55950b27abb5 in output_BLOCK_HEADER ../../programs/dwg2SVG.c:371
    #6 0x55950b278477 in output_SVG ../../programs/dwg2SVG.c:411
    #7 0x55950b278477 in main ../../programs/dwg2SVG.c:525
    #8 0x7f433bac6b96 in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x21b96)
    #9 0x55950b278d19 in _start (/home/user/linhlhq/libredwg/asan_build/programs/dwg2SVG+0x27ad19)

AddressSanitizer can not provide additional info.
SUMMARY: AddressSanitizer: SEGV (/lib/x86_64-linux-gnu/libc.so.6+0xb1645)
==19607==ABORTING
```
Several bugs found by fuzzing
This is a GitHub Issue
repo:libredwg
owner:LibreDWG
Title : Several bugs found by fuzzing
Issue date:

--- start body ---
Hi,
After fuzzing libredwg, I found the following bugs on the latest commit on master.
Command: ./dwg2SVG $PoC
**1.NULL pointer dereference in htmlescape ../../programs/escape.c:29**
POC: https://github.com/linhlhq/research/blob/master/PoCs/libreDWG_7b9cb829/id:000013%2Csig:06%2Csrc:000000%2Cop:flip1%2Cpos:46417
ASAN says:
```
=================================================================
==19607==ERROR: AddressSanitizer: SEGV on unknown address 0x000000000000 (pc 0x7f433bb56646 bp 0x7ffed1176670 sp 0x7ffed1175de8 T0)
==19607==The signal is caused by a READ memory access.
==19607==Hint: address points to the zero page.
    #0 0x7f433bb56645  (/lib/x86_64-linux-gnu/libc.so.6+0xb1645)
    #1 0x7f433c28557b  (/usr/lib/x86_64-linux-gnu/libasan.so.4+0x5157b)
    #2 0x55950b27cdd4 in htmlescape ../../programs/escape.c:29
    #3 0x55950b27abb5 in output_TEXT ../../programs/dwg2SVG.c:113
    #4 0x55950b27abb5 in output_object ../../programs/dwg2SVG.c:312
    #5 0x55950b27abb5 in output_BLOCK_HEADER ../../programs/dwg2SVG.c:371
    #6 0x55950b278477 in output_SVG ../../programs/dwg2SVG.c:411
    #7 0x55950b278477 in main ../../programs/dwg2SVG.c:525
    #8 0x7f433bac6b96 in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x21b96)
    #9 0x55950b278d19 in _start (/home/user/linhlhq/libredwg/asan_build/programs/dwg2SVG+0x27ad19)

AddressSanitizer can not provide additional info.
SUMMARY: AddressSanitizer: SEGV (/lib/x86_64-linux-gnu/libc.so.6+0xb1645)
==19607==ABORTING
```
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