AddressSanitizer: heap-buffer-overflow in function parse_paragraph at ps-pdf.cxx:5203

[hdthky]

Description

Whilst experimenting with htmldoc, built from commit 0bef12c, we are able to induce a vulnerability at htmldoc/htmldoc/ps-pdf.cxx:5203 in function parse_paragraph , using a harness compiled from htmldoc/htmldoc.cxx.

Because there is no bounds checking, a heap-based out-of-bound read will be triggered when the software encounters a malformed file, result in information disclosure or denial of service.

Environment

Ubuntu 20.04

gcc 10.3.0 with ASAN

Proof of Concept

The POC is: poc_heap_overflow7

The command is: ./htmldoc --webpage -t pdf -f /dev/null poc_heap_overflow7

The ASAN report is:

=================================================================
==9833==ERROR: AddressSanitizer: heap-use-after-free on address 0x6080000005d0 at pc 0x5555555d65cd bp 0x7fffffffa220 sp 0x7fffffffa210
READ of size 4 at 0x6080000005d0 thread T0
    #0 0x5555555d65cc in parse_paragraph /work/htmldoc/htmldoc/ps-pdf.cxx:5203
    #1 0x5555555f526e in parse_doc /work/htmldoc/htmldoc/ps-pdf.cxx:4572
    #2 0x5555555f1976 in parse_doc /work/htmldoc/htmldoc/ps-pdf.cxx:4273
    #3 0x5555555f4f23 in parse_doc /work/htmldoc/htmldoc/ps-pdf.cxx:4537
    #4 0x555555604d71 in pspdf_export /work/htmldoc/htmldoc/ps-pdf.cxx:803
    #5 0x55555559f764 in main /work/htmldoc/htmldoc/htmldoc.cxx:1291
    #6 0x7ffff6b620b2 in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x270b2)
    #7 0x55555559fbcd in _start (/work/htmldoc/htmldoc/htmldoc+0x4bbcd)

0x6080000005d0 is located 48 bytes inside of 96-byte region [0x6080000005a0,0x608000000600)
freed by thread T0 here:
    #0 0x7ffff769b8f7 in __interceptor_free ../../../../src/libsanitizer/asan/asan_malloc_linux.cpp:127
    #1 0x5555555d4b91 in parse_paragraph /work/htmldoc/htmldoc/ps-pdf.cxx:4881

previously allocated by thread T0 here:
    #0 0x7ffff769be17 in __interceptor_calloc ../../../../src/libsanitizer/asan/asan_malloc_linux.cpp:154
    #1 0x5555555d0470 in flatten_tree /work/htmldoc/htmldoc/ps-pdf.cxx:9585

SUMMARY: AddressSanitizer: heap-use-after-free /work/htmldoc/htmldoc/ps-pdf.cxx:5203 in parse_paragraph
Shadow bytes around the buggy address:
  0x0c107fff8060: fa fa fa fa 00 00 00 00 00 00 00 00 00 00 00 00
  0x0c107fff8070: fa fa fa fa 00 00 00 00 00 00 00 00 00 00 00 00
  0x0c107fff8080: fa fa fa fa 00 00 00 00 00 00 00 00 00 00 00 00
  0x0c107fff8090: fa fa fa fa 00 00 00 00 00 00 00 00 00 00 00 00
  0x0c107fff80a0: fa fa fa fa 00 00 00 00 00 00 00 00 00 00 00 00
=>0x0c107fff80b0: fa fa fa fa fd fd fd fd fd fd[fd]fd fd fd fd fd
  0x0c107fff80c0: fa fa fa fa 00 00 00 00 00 00 00 00 00 00 00 00
  0x0c107fff80d0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c107fff80e0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c107fff80f0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c107fff8100: 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
==9833==ABORTING

Impact

This vulnerability is capable of inducing information disclosure or denial of service.

[michaelrsweet]

Denial of service perhaps, information disclosure unlikely.

[hdthky]

Maybe I misrepresent it, I just wanted to say it's possible.

[michaelrsweet]

Needed to update prev pointer in linked list:

[master 614fcba] Fix potential use-after-free in blocks/paragraphs (Issue #484)