GNU LibreDWG 0.9.3.2564 has a heap-based buffer over-read in bit_search_sentinel in bits.c.
Hi,
After fuzzing libredwg, I found the following bugs on the latest commit on master.
Command: ./dwg2svg2 $PoC
**1.heap-buffer-overflow in read_pages_map ../../src/decode_r2007.c:1007**
POC: https://github.com/linhlhq/research/blob/master/PoCs/libreDWG_0.9.3.2564/id:000239%2Csig:06%2Csrc:007083%2Cop:havoc%2Crep:4
ASAN says:
```
==4335==ERROR: AddressSanitizer: heap-buffer-overflow on address 0x611000000258 at pc 0x55f9e1e04e05 bp 0x7ffc92f94a40 sp 0x7ffc92f94a30
READ of size 8 at 0x611000000258 thread T0
    #0 0x55f9e1e04e04 in read_pages_map ../../src/decode_r2007.c:1007
    #1 0x55f9e1e04e04 in read_r2007_meta_data ../../src/decode_r2007.c:1774
    #2 0x55f9e1dd66d7 in decode_R2007 ../../src/decode.c:2973
    #3 0x55f9e1dd66d7 in dwg_decode ../../src/decode.c:241
    #4 0x55f9e177b466 in dwg_read_file ../../src/dwg.c:210
    #5 0x55f9e1776d4b in test_SVG ../../examples/dwg2svg2.c:116
    #6 0x55f9e1776d4b in main ../../examples/dwg2svg2.c:501
    #7 0x7f595f806b96 in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x21b96)
    #8 0x55f9e17779a9 in _start (/home/user/linhlhq/libredwg/asan_build/examples/dwg2svg2+0x2d59a9)

0x61100000025c is located 0 bytes to the right of 220-byte region [0x611000000180,0x61100000025c)
allocated by thread T0 here:
    #0 0x7f5960052d38 in __interceptor_calloc (/usr/lib/x86_64-linux-gnu/libasan.so.4+0xded38)
    #1 0x55f9e1de73be in read_system_page ../../src/decode_r2007.c:635

SUMMARY: AddressSanitizer: heap-buffer-overflow ../../src/decode_r2007.c:1007 in read_pages_map
Shadow bytes around the buggy address:
  0x0c227fff7ff0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x0c227fff8000: fa fa fa fa fa fa fa fa 00 00 00 00 00 00 00 00
  0x0c227fff8010: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x0c227fff8020: 00 00 00 00 00 00 fa fa fa fa fa fa fa fa fa fa
  0x0c227fff8030: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
=>0x0c227fff8040: 00 00 00 00 00 00 00 00 00 00 00[04]fa fa fa fa
  0x0c227fff8050: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c227fff8060: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c227fff8070: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c227fff8080: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c227fff8090: 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
==4335==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: ./dwg2svg2 $PoC
**1.heap-buffer-overflow in read_pages_map ../../src/decode_r2007.c:1007**
POC: https://github.com/linhlhq/research/blob/master/PoCs/libreDWG_0.9.3.2564/id:000239%2Csig:06%2Csrc:007083%2Cop:havoc%2Crep:4
ASAN says:
```
==4335==ERROR: AddressSanitizer: heap-buffer-overflow on address 0x611000000258 at pc 0x55f9e1e04e05 bp 0x7ffc92f94a40 sp 0x7ffc92f94a30
READ of size 8 at 0x611000000258 thread T0
    #0 0x55f9e1e04e04 in read_pages_map ../../src/decode_r2007.c:1007
    #1 0x55f9e1e04e04 in read_r2007_meta_data ../../src/decode_r2007.c:1774
    #2 0x55f9e1dd66d7 in decode_R2007 ../../src/decode.c:2973
    #3 0x55f9e1dd66d7 in dwg_decode ../../src/decode.c:241
    #4 0x55f9e177b466 in dwg_read_file ../../src/dwg.c:210
    #5 0x55f9e1776d4b in test_SVG ../../examples/dwg2svg2.c:116
    #6 0x55f9e1776d4b in main ../../examples/dwg2svg2.c:501
    #7 0x7f595f806b96 in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x21b96)
    #8 0x55f9e17779a9 in _start (/home/user/linhlhq/libredwg/asan_build/examples/dwg2svg2+0x2d59a9)

0x61100000025c is located 0 bytes to the right of 220-byte region [0x611000000180,0x61100000025c)
allocated by thread T0 here:
    #0 0x7f5960052d38 in __interceptor_calloc (/usr/lib/x86_64-linux-gnu/libasan.so.4+0xded38)
    #1 0x55f9e1de73be in read_system_page ../../src/decode_r2007.c:635

SUMMARY: AddressSanitizer: heap-buffer-overflow ../../src/decode_r2007.c:1007 in read_pages_map
Shadow bytes around the buggy address:
  0x0c227fff7ff0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x0c227fff8000: fa fa fa fa fa fa fa fa 00 00 00 00 00 00 00 00
  0x0c227fff8010: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x0c227fff8020: 00 00 00 00 00 00 fa fa fa fa fa fa fa fa fa fa
  0x0c227fff8030: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
=>0x0c227fff8040: 00 00 00 00 00 00 00 00 00 00 00[04]fa fa fa fa
  0x0c227fff8050: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c227fff8060: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c227fff8070: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c227fff8080: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c227fff8090: 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
==4335==ABORTING
```
--- end body ---

A heap buffer overflow vulnerability in the read_pages_map function of LibreDWG allows attackers to potentially execute arbitrary code or cause a Denial of Service (DoS) by providing specially crafted DWG files. This issue was identified through fuzzing, which revealed that the program attempts to read beyond allocated memory, leading to a segmentation fault.