Buffer Overflow vulnerability found in Cesanta MJS v.1.26 allows a local attacker to cause a denial of service via the mjs_mk_string function in mjs.c.
cpe:2.3:a:cesanta:mjs:1.26:*:*:*:*:*:*:*
25C97820-C80A-41CE-B510-F292D2AF665E
OR
Heap buffer overflow in mjs at function mjs_mk_string in mjs.c:13671.

## Environment
Ubuntu 18.04, 64 bit

## Steps to reproduce
1. download file
```
git clone https://github.com/cesanta/mjs.git mjs
cd mjs
git checkout 9eae0e6
```
2. compile libming with ASAN
```
clang -fsanitize=address mjs.c -o mjs_asan
```
3. command for reproducing the error
```
./mjs_asan -f poc
```
Download poc: 
[mjs_heap-buffer-overflow_mjs13671.zip](https://github.com/cesanta/mjs/files/11038286/mjs_heap-buffer-overflow_mjs13671.zip)

## ASAN report
```
> ./mjs_asan -f mjs_heap-buffer-overflow_mjs13671
=================================================================
==23460==ERROR: AddressSanitizer: heap-buffer-overflow on address 0x60800000007d at pc 0x00000046b929 bp 0x7fff87d05cd0 sp 0x7fff87d05480
READ of size 94 at 0x60800000007d thread T0
    #0 0x46b928 in __interceptor_strlen.part.0 /home/fzz/Desktop/STFGFuzz/LLVM/llvm/projects/compiler-rt/lib/asan/../sanitizer_common/sanitizer_common_interceptors.inc:372:5
    #1 0x510fbf in mjs_mk_string /root/compiler1804/aflgo_dataset/mjs-issues-78/mjs.c:13671:35
    #2 0x5328d2 in frozen_cb /root/compiler1804/aflgo_dataset/mjs-issues-78/mjs.c:11870:13
    #3 0x5162ac in parse_string /root/compiler1804/aflgo_dataset/mjs-issues-78/mjs.c:5884:9
    #4 0x51597c in parse_value /root/compiler1804/aflgo_dataset/mjs-issues-78/mjs.c:5970:7
    #5 0x516bb3 in parse_array /root/compiler1804/aflgo_dataset/mjs-issues-78/mjs.c:5936:9
    #6 0x515a94 in parse_value /root/compiler1804/aflgo_dataset/mjs-issues-78/mjs.c:5976:7
    #7 0x503145 in doit /root/compiler1804/aflgo_dataset/mjs-issues-78/mjs.c:6058:10
    #8 0x50077b in json_walk /root/compiler1804/aflgo_dataset/mjs-issues-78/mjs.c:6434:3
    #9 0x532618 in mjs_json_parse /root/compiler1804/aflgo_dataset/mjs-issues-78/mjs.c:11963:14
    #10 0x50a501 in mjs_op_json_parse /root/compiler1804/aflgo_dataset/mjs-issues-78/mjs.c:12012:5
    #11 0x50e248 in mjs_execute /root/compiler1804/aflgo_dataset/mjs-issues-78/mjs.c:9541:11
    #12 0x50c4ce in mjs_exec_internal /root/compiler1804/aflgo_dataset/mjs-issues-78/mjs.c:9758:5
    #13 0x50c610 in mjs_exec_file /root/compiler1804/aflgo_dataset/mjs-issues-78/mjs.c:9781:11
    #14 0x50fe4f in main /root/compiler1804/aflgo_dataset/mjs-issues-78/mjs.c:12051:13
    #15 0x7f5460494082 in __libc_start_main /build/glibc-SzIz7B/glibc-2.31/csu/../csu/libc-start.c:308:16
    #16 0x41c3cd in _start (/home/fzz/Desktop/STFGFuzz/Programs/mjs-issues-78/seeds_crash/mjs_asan+0x41c3cd)

0x60800000007d is located 0 bytes to the right of 93-byte region [0x608000000020,0x60800000007d)
allocated by thread T0 here:
    #0 0x4c1f3f in malloc /home/fzz/Desktop/STFGFuzz/LLVM/llvm/projects/compiler-rt/lib/asan/asan_malloc_linux.cpp:145:3
    #1 0x53287b in frozen_cb /root/compiler1804/aflgo_dataset/mjs-issues-78/mjs.c:11868:36
    #2 0x5162ac in parse_string /root/compiler1804/aflgo_dataset/mjs-issues-78/mjs.c:5884:9
    #3 0x51597c in parse_value /root/compiler1804/aflgo_dataset/mjs-issues-78/mjs.c:5970:7
    #4 0x516bb3 in parse_array /root/compiler1804/aflgo_dataset/mjs-issues-78/mjs.c:5936:9
    #5 0x515a94 in parse_value /root/compiler1804/aflgo_dataset/mjs-issues-78/mjs.c:5976:7
    #6 0x503145 in doit /root/compiler1804/aflgo_dataset/mjs-issues-78/mjs.c:6058:10
    #7 0x50077b in json_walk /root/compiler1804/aflgo_dataset/mjs-issues-78/mjs.c:6434:3
    #8 0x532618 in mjs_json_parse /root/compiler1804/aflgo_dataset/mjs-issues-78/mjs.c:11963:14
    #9 0x50a501 in mjs_op_json_parse /root/compiler1804/aflgo_dataset/mjs-issues-78/mjs.c:12012:5
    #10 0x50e248 in mjs_execute /root/compiler1804/aflgo_dataset/mjs-issues-78/mjs.c:9541:11
    #11 0x50c4ce in mjs_exec_internal /root/compiler1804/aflgo_dataset/mjs-issues-78/mjs.c:9758:5
    #12 0x50c610 in mjs_exec_file /root/compiler1804/aflgo_dataset/mjs-issues-78/mjs.c:9781:11
    #13 0x50fe4f in main /root/compiler1804/aflgo_dataset/mjs-issues-78/mjs.c:12051:13
    #14 0x7f5460494082 in __libc_start_main /build/glibc-SzIz7B/glibc-2.31/csu/../csu/libc-start.c:308:16

SUMMARY: AddressSanitizer: heap-buffer-overflow /home/fzz/Desktop/STFGFuzz/LLVM/llvm/projects/compiler-rt/lib/asan/../sanitizer_common/sanitizer_common_interceptors.inc:372:5 in __interceptor_strlen.part.0
Shadow bytes around the buggy address:
  0x0c107fff7fb0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x0c107fff7fc0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x0c107fff7fd0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x0c107fff7fe0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x0c107fff7ff0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
=>0x0c107fff8000: fa fa fa fa 00 00 00 00 00 00 00 00 00 00 00[05]
  0x0c107fff8010: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c107fff8020: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c107fff8030: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c107fff8040: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c107fff8050: 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
  Shadow gap:              cc
==23460==ABORTING

```
Heap buffer overflow in mjs_mk_string() at mjs.c:13671
This is a GitHub Issue
repo:mjs
owner:cesanta
Title : Heap buffer overflow in mjs_mk_string() at mjs.c:13671
Issue date:

--- start body ---
Heap buffer overflow in mjs at function mjs_mk_string in mjs.c:13671.

## Environment
Ubuntu 18.04, 64 bit

## Steps to reproduce
1. download file
```
git clone https://github.com/cesanta/mjs.git mjs
cd mjs
git checkout 9eae0e6
```
2. compile libming with ASAN
```
clang -fsanitize=address mjs.c -o mjs_asan
```
3. command for reproducing the error
```
./mjs_asan -f poc
```
Download poc: 
[mjs_heap-buffer-overflow_mjs13671.zip](https://github.com/cesanta/mjs/files/11038286/mjs_heap-buffer-overflow_mjs13671.zip)

## ASAN report
```
> ./mjs_asan -f mjs_heap-buffer-overflow_mjs13671
=================================================================
==23460==ERROR: AddressSanitizer: heap-buffer-overflow on address 0x60800000007d at pc 0x00000046b929 bp 0x7fff87d05cd0 sp 0x7fff87d05480
READ of size 94 at 0x60800000007d thread T0
    #0 0x46b928 in __interceptor_strlen.part.0 /home/fzz/Desktop/STFGFuzz/LLVM/llvm/projects/compiler-rt/lib/asan/../sanitizer_common/sanitizer_common_interceptors.inc:372:5
    #1 0x510fbf in mjs_mk_string /root/compiler1804/aflgo_dataset/mjs-issues-78/mjs.c:13671:35
    #2 0x5328d2 in frozen_cb /root/compiler1804/aflgo_dataset/mjs-issues-78/mjs.c:11870:13
    #3 0x5162ac in parse_string /root/compiler1804/aflgo_dataset/mjs-issues-78/mjs.c:5884:9
    #4 0x51597c in parse_value /root/compiler1804/aflgo_dataset/mjs-issues-78/mjs.c:5970:7
    #5 0x516bb3 in parse_array /root/compiler1804/aflgo_dataset/mjs-issues-78/mjs.c:5936:9
    #6 0x515a94 in parse_value /root/compiler1804/aflgo_dataset/mjs-issues-78/mjs.c:5976:7
    #7 0x503145 in doit /root/compiler1804/aflgo_dataset/mjs-issues-78/mjs.c:6058:10
    #8 0x50077b in json_walk /root/compiler1804/aflgo_dataset/mjs-issues-78/mjs.c:6434:3
    #9 0x532618 in mjs_json_parse /root/compiler1804/aflgo_dataset/mjs-issues-78/mjs.c:11963:14
    #10 0x50a501 in mjs_op_json_parse /root/compiler1804/aflgo_dataset/mjs-issues-78/mjs.c:12012:5
    #11 0x50e248 in mjs_execute /root/compiler1804/aflgo_dataset/mjs-issues-78/mjs.c:9541:11
    #12 0x50c4ce in mjs_exec_internal /root/compiler1804/aflgo_dataset/mjs-issues-78/mjs.c:9758:5
    #13 0x50c610 in mjs_exec_file /root/compiler1804/aflgo_dataset/mjs-issues-78/mjs.c:9781:11
    #14 0x50fe4f in main /root/compiler1804/aflgo_dataset/mjs-issues-78/mjs.c:12051:13
    #15 0x7f5460494082 in __libc_start_main /build/glibc-SzIz7B/glibc-2.31/csu/../csu/libc-start.c:308:16
    #16 0x41c3cd in _start (/home/fzz/Desktop/STFGFuzz/Programs/mjs-issues-78/seeds_crash/mjs_asan+0x41c3cd)

0x60800000007d is located 0 bytes to the right of 93-byte region [0x608000000020,0x60800000007d)
allocated by thread T0 here:
    #0 0x4c1f3f in malloc /home/fzz/Desktop/STFGFuzz/LLVM/llvm/projects/compiler-rt/lib/asan/asan_malloc_linux.cpp:145:3
    #1 0x53287b in frozen_cb /root/compiler1804/aflgo_dataset/mjs-issues-78/mjs.c:11868:36
    #2 0x5162ac in parse_string /root/compiler1804/aflgo_dataset/mjs-issues-78/mjs.c:5884:9
    #3 0x51597c in parse_value /root/compiler1804/aflgo_dataset/mjs-issues-78/mjs.c:5970:7
    #4 0x516bb3 in parse_array /root/compiler1804/aflgo_dataset/mjs-issues-78/mjs.c:5936:9
    #5 0x515a94 in parse_value /root/compiler1804/aflgo_dataset/mjs-issues-78/mjs.c:5976:7
    #6 0x503145 in doit /root/compiler1804/aflgo_dataset/mjs-issues-78/mjs.c:6058:10
    #7 0x50077b in json_walk /root/compiler1804/aflgo_dataset/mjs-issues-78/mjs.c:6434:3
    #8 0x532618 in mjs_json_parse /root/compiler1804/aflgo_dataset/mjs-issues-78/mjs.c:11963:14
    #9 0x50a501 in mjs_op_json_parse /root/compiler1804/aflgo_dataset/mjs-issues-78/mjs.c:12012:5
    #10 0x50e248 in mjs_execute /root/compiler1804/aflgo_dataset/mjs-issues-78/mjs.c:9541:11
    #11 0x50c4ce in mjs_exec_internal /root/compiler1804/aflgo_dataset/mjs-issues-78/mjs.c:9758:5
    #12 0x50c610 in mjs_exec_file /root/compiler1804/aflgo_dataset/mjs-issues-78/mjs.c:9781:11
    #13 0x50fe4f in main /root/compiler1804/aflgo_dataset/mjs-issues-78/mjs.c:12051:13
    #14 0x7f5460494082 in __libc_start_main /build/glibc-SzIz7B/glibc-2.31/csu/../csu/libc-start.c:308:16

SUMMARY: AddressSanitizer: heap-buffer-overflow /home/fzz/Desktop/STFGFuzz/LLVM/llvm/projects/compiler-rt/lib/asan/../sanitizer_common/sanitizer_common_interceptors.inc:372:5 in __interceptor_strlen.part.0
Shadow bytes around the buggy address:
  0x0c107fff7fb0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x0c107fff7fc0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x0c107fff7fd0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x0c107fff7fe0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x0c107fff7ff0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
=>0x0c107fff8000: fa fa fa fa 00 00 00 00 00 00 00 00 00 00 00[05]
  0x0c107fff8010: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c107fff8020: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c107fff8030: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c107fff8040: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c107fff8050: 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
  Shadow gap:              cc
==23460==ABORTING

```
--- end body ---

comments :
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