Heap buffer overflow in the yySet function
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Problem Description
Note: I am aware that this project is unmaintained. However, I am still opening this issue to follow CVE's guidelines for EOL software.
There is a heap buffer overflow in the yySet
function when the parser handles a specially crafted Markdown file. In particular, there's an out-of-bounds write to the heap left redzone, which is part of the heap header metadata.
Here is a minimized proof-of-concept Markdown file that triggers the bug: min_heap_overflow.md. The output is as follows:
=================================================================
==3241393==ERROR: AddressSanitizer: heap-buffer-overflow on address 0x611000000280 at pc 0x0000004c6a36 bp 0x7fffffffe0c0 sp 0x7fffffffe0b8
WRITE of size 8 at 0x611000000280 thread T0
#0 0x4c6a35 in yySet /home/sanic/peg-markdown/markdown_parser.c:288:80
#1 0x5d45a1 in yyDone /home/sanic/peg-markdown/markdown_parser.c:255:7
#2 0x5d45a1 in yyparsefrom /home/sanic/peg-markdown/markdown_parser.c:6736:13
#3 0x5de691 in parse_markdown /home/sanic/peg-markdown/parsing_functions.c:112:5
#4 0x5dca1c in markdown_to_g_string /home/sanic/peg-markdown/markdown_lib.c:157:14
#5 0x5dce84 in markdown_to_string /home/sanic/peg-markdown/markdown_lib.c:175:11
#6 0x4c4d06 in main /home/sanic/peg-markdown/markdown.c:180:11
#7 0x7ffff7b25082 in __libc_start_main /build/glibc-SzIz7B/glibc-2.31/csu/../csu/libc-start.c:308:16
#8 0x41c50d in _start (/home/sanic/peg-markdown/markdown+0x41c50d)
0x611000000280 is located 0 bytes to the right of 256-byte region [0x611000000180,0x611000000280)
allocated by thread T0 here:
#0 0x494c4d in malloc (/home/sanic/peg-markdown/markdown+0x494c4d)
#1 0x5d4164 in yyparsefrom /home/sanic/peg-markdown/markdown_parser.c:6729:31
SUMMARY: AddressSanitizer: heap-buffer-overflow /home/sanic/peg-markdown/markdown_parser.c:288:80 in yySet
Shadow bytes around the buggy address:
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 00 04 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 00 00 00 00 00
=>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
0x0c227fff80a0: 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
==3241393==ABORTING
Reproduction Steps
- Compile the project using ASAN (Address Sanitizer). For example,
CC=afl-clang-fast AFL_USE_ASAN=1 make
. - Run
./markdown -x min_heap_overflow.md
(use the proof-of-concept file attached to this report). - Observe the heap buffer overflow in the output.