$ ./mjs/build/mjs poc.js
==122636==ERROR: AddressSanitizer: heap-buffer-overflow on address 0x61500000007f at pc 0x00000057b751 bp 0x7fff091bd080 sp 0x7fff091bd078
WRITE of size 1 at 0x61500000007f thread T0
#0 0x57b750 in to_json_or_debug /root/mjs/src/mjs_json.c:154:13
#1 0x55178f in mjs_exec_internal /root/mjs/src/mjs_exec.c:1073:5
#2 0x552d2d in mjs_exec_file /root/mjs/src/mjs_exec.c:1096:11
#3 0x5821d3 in main /root/mjs/src/mjs_main.c:47:11
#4 0x7f2516c85b96 in __libc_start_main /build/glibc-2ORdQG/glibc-2.27/csu/../csu/libc-start.c:310
#5 0x41a2c9 in _start (/usr/local/bin/mjs+0x41a2c9)
0x61500000007f is located 1 bytes to the left of 472-byte region [0x615000000080,0x615000000258)
allocated by thread T0 here:
#0 0x4da3a8 in calloc (/usr/local/bin/mjs+0x4da3a8)
#1 0x538c1a in mjs_create /root/mjs/src/mjs_core.c:74:21
#2 0x5817e1 in main /root/mjs/src/mjs_main.c:17:21
#3 0x7f2516c85b96 in __libc_start_main /build/glibc-2ORdQG/glibc-2.27/csu/../csu/libc-start.c:310
SUMMARY: AddressSanitizer: heap-buffer-overflow /root/mjs/src/mjs_json.c:154:13 in to_json_or_debug
Shadow bytes around the buggy address:
0x0c2a7fff7fb0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
0x0c2a7fff7fc0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
0x0c2a7fff7fd0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
0x0c2a7fff7fe0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
0x0c2a7fff7ff0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
=>0x0c2a7fff8000: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa[fa]
0x0c2a7fff8010: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
0x0c2a7fff8020: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
0x0c2a7fff8030: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
0x0c2a7fff8040: 00 00 00 00 00 00 00 00 00 00 00 fa fa fa fa fa
0x0c2a7fff8050: 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
==122636==ABORTING
mJS revision
Commit: b1b6eac
Build steps
Test case
poc.js
Execution steps & Output
Credits: Found by OWL337 team.