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mity / md4c

C Markdown parser. Fast. SAX-like interface. Compliant to CommonMark specification.
MIT License
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Multiple vulnerabilities in md4c #36

Closed ChijinZ closed 6 years ago

ChijinZ commented 6 years ago

Multiple vulnerabilities in md4c

There are multiple vulnerabilities in md4c (git repository: https://github.com/mity/md4c, Latest commit 81e2a5c on Apr 12, 2018).

git log 

commit 81e2a5cac2c8c2b1f8fe63b7bce3fe7e516e2891
Author: Martin Mitas <mity@morous.org>
Date:   Thu Apr 12 17:03:37 2018 +0200

Heap buffer overflow in md_split_simple_pairing_mark()

command: ./md2html testfile

testcase: https://github.com/ChijinZ/security_advisories/blob/master/md4c-81e2a5c/Heap_buffer_overflow_in_md_split_simple_pairing_mark

It seems like that an overflow happened in memcpy() in md4c.c:3499:

memcpy(dummy, mark, sizeof(MD_MARK));

AddressSanitizer provided information as below:

==27938==ERROR: AddressSanitizer: heap-buffer-overflow on address 0x61a000000684 at pc 0x0000004dd7f5 bp 0x7ffedcfedc30 sp 0x7ffedcfed3e0
WRITE of size 20 at 0x61a000000684 thread T0
    #0 0x4dd7f4 in __asan_memcpy /home/ubuntu/llvm/llvm-6.0.0.src/projects/compiler-rt/lib/asan/asan_interceptors_memintrinsics.cc:23
    #1 0x546dd3 in md_split_simple_pairing_mark /home/ubuntu/fuzz/test/md4c/md4c/md4c.c:3499:5
    #2 0x546dd3 in md_analyze_simple_pairing_mark /home/ubuntu/fuzz/test/md4c/md4c/md4c.c:3553
    #3 0x540584 in md_analyze_marks /home/ubuntu/fuzz/test/md4c/md4c/md4c.c
    #4 0x53c9c8 in md_analyze_link_contents /home/ubuntu/fuzz/test/md4c/md4c/md4c.c:3813:5
    #5 0x53c9c8 in md_analyze_inlines /home/ubuntu/fuzz/test/md4c/md4c/md4c.c:3802
    #6 0x550b95 in md_process_normal_block_contents /home/ubuntu/fuzz/test/md4c/md4c/md4c.c:4283:5
    #7 0x52e7f7 in md_process_leaf_block /home/ubuntu/fuzz/test/md4c/md4c/md4c.c:4454:13
    #8 0x52e7f7 in md_process_all_blocks /home/ubuntu/fuzz/test/md4c/md4c/md4c.c:4529
    #9 0x52e7f7 in md_process_doc /home/ubuntu/fuzz/test/md4c/md4c/md4c.c:5856
    #10 0x5202cb in md_parse /home/ubuntu/fuzz/test/md4c/md4c/md4c.c:5917:11
    #11 0x51a7a8 in md_render_html /home/ubuntu/fuzz/test/md4c/md2html/render_html.c:488:12
    #12 0x5195cc in process_file /home/ubuntu/fuzz/test/md4c/md2html/md2html.c:139:11
    #13 0x5195cc in main /home/ubuntu/fuzz/test/md4c/md2html/md2html.c:343
    #14 0x7f17c6fc582f in __libc_start_main /build/glibc-Cl5G7W/glibc-2.23/csu/../csu/libc-start.c:291
    #15 0x41a668 in _start (/home/ubuntu/fuzz/test/md4c/build/md2html/md2html+0x41a668)

Address 0x61a000000684 is a wild pointer.
SUMMARY: AddressSanitizer: heap-buffer-overflow /home/ubuntu/llvm/llvm-6.0.0.src/projects/compiler-rt/lib/asan/asan_interceptors_memintrinsics.cc:23 in __asan_memcpy
Shadow bytes around the buggy address:
0x0c347fff8080: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
0x0c347fff8090: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
0x0c347fff80a0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
0x0c347fff80b0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
0x0c347fff80c0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
=>0x0c347fff80d0:[fa]fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
0x0c347fff80e0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
0x0c347fff80f0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
0x0c347fff8100: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
0x0c347fff8110: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
0x0c347fff8120: 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
==27938==ABORTING

Heap buffer overflow in md_process_inlines()

command: ./md2html testfile

testcase: https://github.com/ChijinZ/security_advisories/blob/master/md4c-81e2a5c/Heap_buffer_overflow_in_md_process_inlines

It seems like that mark variable access a restricted area of memory in md4c.c:4004:

while(!(mark->flags & MD_MARK_RESOLVED) || mark->beg < off)

AddressSanitizer provided information as below:

==29037==ERROR: AddressSanitizer: heap-buffer-overflow on address 0x61e000000a91 at pc 0x000000553328 bp 0x7fffe3bdfa70 sp 0x7fffe3bdfa68
READ of size 1 at 0x61e000000a91 thread T0
    #0 0x553327 in md_process_inlines /home/ubuntu/fuzz/test/md4c/md4c/md4c.c:4004:27
    #1 0x553327 in md_process_normal_block_contents /home/ubuntu/fuzz/test/md4c/md4c/md4c.c:4284
    #2 0x52e7f7 in md_process_leaf_block /home/ubuntu/fuzz/test/md4c/md4c/md4c.c:4454:13
    #3 0x52e7f7 in md_process_all_blocks /home/ubuntu/fuzz/test/md4c/md4c/md4c.c:4529
    #4 0x52e7f7 in md_process_doc /home/ubuntu/fuzz/test/md4c/md4c/md4c.c:5856
    #5 0x5202cb in md_parse /home/ubuntu/fuzz/test/md4c/md4c/md4c.c:5917:11
    #6 0x51a7a8 in md_render_html /home/ubuntu/fuzz/test/md4c/md2html/render_html.c:488:12
    #7 0x5195cc in process_file /home/ubuntu/fuzz/test/md4c/md2html/md2html.c:139:11
    #8 0x5195cc in main /home/ubuntu/fuzz/test/md4c/md2html/md2html.c:343
    #9 0x7f49ca83682f in __libc_start_main /build/glibc-Cl5G7W/glibc-2.23/csu/../csu/libc-start.c:291
    #10 0x41a668 in _start (/home/ubuntu/fuzz/test/md4c/build/md2html/md2html+0x41a668)

0x61e000000a91 is located 17 bytes to the right of 2560-byte region [0x61e000000080,0x61e000000a80)
allocated by thread T0 here:
    #0 0x4ded00 in realloc /home/ubuntu/llvm/llvm-6.0.0.src/projects/compiler-rt/lib/asan/asan_malloc_linux.cc:107
    #1 0x5369af in md_push_mark /home/ubuntu/fuzz/test/md4c/md4c/md4c.c:2496:21
    #2 0x5369af in md_collect_marks /home/ubuntu/fuzz/test/md4c/md4c/md4c.c:2897
    #3 0x5369af in md_analyze_inlines /home/ubuntu/fuzz/test/md4c/md4c/md4c.c:3774
    #4 0x550b95 in md_process_normal_block_contents /home/ubuntu/fuzz/test/md4c/md4c/md4c.c:4283:5

SUMMARY: AddressSanitizer: heap-buffer-overflow /home/ubuntu/fuzz/test/md4c/md4c/md4c.c:4004:27 in md_process_inlines
Shadow bytes around the buggy address:
0x0c3c7fff8100: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
0x0c3c7fff8110: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
0x0c3c7fff8120: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
0x0c3c7fff8130: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
0x0c3c7fff8140: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
=>0x0c3c7fff8150: fa fa[fa]fa fa fa fa fa fa fa fa fa fa fa fa fa
0x0c3c7fff8160: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
0x0c3c7fff8170: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
0x0c3c7fff8180: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
0x0c3c7fff8190: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
0x0c3c7fff81a0: 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
==29037==ABORTING
mity commented 6 years ago

Thanks for the report. I'll take a look at it.

Please next time open one issue per incident, it's better if any discussion arises.

mity commented 6 years ago

Minimized the 2nd issue into this:

__x_ _x___
mity commented 6 years ago

I was mainly analyzing/debugging the 2nd issue but the fix seems to resolve both.