Project: libredwg (libredwg/libredwg), language: c++
Vulnerability instance: libredwg.cve-2021-39525
Sanitizer: address

================= Bug Report (1/1) ==================
## Source: GitHub Issue
## URL: https://github.com/LibreDWG/libredwg/issues/261
## Description:
Issue: LibreDWG/libredwg#261
Title: A heap overflow in bits.c:1424
State: closed
Created by: seviezhou
Created at: 2020-08-02 04:51:37+00:00
Labels: bug, fuzzing

Issue Body:
## System info

Ubuntu X64, gcc (Ubuntu 5.5.0-12ubuntu1), dwg2dxf (latest master [39ef943](https://github.com/LibreDWG/libredwg/commit/39ef9439f35111170258cf57cc0c58eabc4748c7))

## Configure

CFLAGS="-g -fsanitize=address" LDFLAGS="-fsanitize=address" ./configure

## Command line

./programs/dwg2dxf -b -m ./SEGV-check_POLYLINE_handles-decode-5110 -o /dev/null

## AddressSanitizer output

```
=================================================================
==65289==ERROR: AddressSanitizer: heap-buffer-overflow on address 0x62c0000381ff at pc 0x7fc1be68a945 bp 0x7fff3419f990 sp 0x7fff3419f138
READ of size 6 at 0x62c0000381ff thread T0
    #0 0x7fc1be68a944 in __asan_memcpy (/usr/lib/x86_64-linux-gnu/libasan.so.2+0x8c944)
    #1 0x5588916f116f in memcpy /usr/include/x86_64-linux-gnu/bits/string_fortified.h:34
    #2 0x5588916f116f in bit_read_fixed /home/seviezhou/libredwg/src/bits.c:1424
    #3 0x558891715678 in acds_private /home/seviezhou/libredwg/src/acds.spec:111
    #4 0x5588917b3161 in read_2004_section_acds /home/seviezhou/libredwg/src/decode.c:3437
    #5 0x5588917b3161 in decode_R2004 /home/seviezhou/libredwg/src/decode.c:3694
    #6 0x5588917bf646 in dwg_decode /home/seviezhou/libredwg/src/decode.c:242
    #7 0x5588916b89fc in dwg_read_file /home/seviezhou/libredwg/src/dwg.c:251
    #8 0x5588916b5e12 in main /home/seviezhou/libredwg/programs/dwg2dxf.c:258
    #9 0x7fc1bde90b96 in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x21b96)
    #10 0x5588916b6d69 in _start (/home/seviezhou/libredwg/programs/dwg2dxf+0xa88d69)

0x62c0000381ff is located 1 bytes to the left of 29696-byte region [0x62c000038200,0x62c00003f600)
allocated by thread T0 here:
    #0 0x7fc1be6967aa in __interceptor_calloc (/usr/lib/x86_64-linux-gnu/libasan.so.2+0x987aa)
    #1 0x5588917211c4 in read_2004_compressed_section /home/seviezhou/libredwg/src/decode.c:2432
    #2 0x5588922c13aa  (/home/seviezhou/libredwg/programs/dwg2dxf+0x16933aa)

SUMMARY: AddressSanitizer: heap-buffer-overflow ??:0 __asan_memcpy
Shadow bytes around the buggy address:
  0x0c587fffefe0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c587fffeff0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c587ffff000: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c587ffff010: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c587ffff020: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
=>0x0c587ffff030: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa[fa]
  0x0c587ffff040: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x0c587ffff050: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x0c587ffff060: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x0c587ffff070: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x0c587ffff080: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
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
==65289==ABORTING
```

## POC

[heap-overflow-bit_read_fixed-bits-1424.zip](https://github.com/LibreDWG/libredwg/files/5011661/heap-overflow-bit_read_fixed-bits-1424.zip)



Comments:
Comment by rurban on 2020-08-02 11:01:52+00:00:
This was already fixed with the ACDS.num_segidxf check in GH #259 
Not repro anymore

Attachments:
https://github.com/LibreDWG/libredwg/files/5011661/heap-overflow-bit_read_fixed-bits-1424.zip

Commit References:
39ef9439f35111170258cf57cc0c58eabc4748c7

Build script:
#!/bin/bash -eu
# Minimized build script with only core build commands
set -eu
sh ./autogen.sh
./configure --disable-shared
make -j$(nproc)

Dockerfile:
FROM hwiwonlee/secb.base:latest
RUN apt-get update && apt-get install -y autoconf libtool texinfo
RUN git clone https://github.com/libredwg/libredwg libredwg
RUN git -C libredwg checkout aee0ea1f52ef9603b981362c83b3fec324ebb199
WORKDIR $SRC/libredwg
COPY build.sh $SRC/

Additional files:
filename: fuzz_dwg_decode.options
content: [libfuzzer]
detect_leaks=0