CVE-2022-45496: Heap Overflow in json.h(json_parse_string())

In json_parse_string() function of json.h(https://github.com/sheredom/json.h), there is a heap out-of-bound write. The bug can be triggered with an invocation of json_parse_ex() with a specific flags combination. The root cause of the vulnerability is when copying from src to data, the length of data(state.data_size) is not taken into consideration of. This may cause EoP when using json.h as incoming json data parser.

The flags is 0x5fd6d7d6d6247bff
=================================================================
==4928==ERROR: AddressSanitizer: heap-buffer-overflow on address 0x613000000189 at pc 0x55b62d1096ee bp 0x7ffdc2d4b010 sp 0x7ffdc2d4b008
WRITE of size 1 at 0x613000000189 thread T0
    #0 0x55b62d1096ed in json_parse_string /home/hyrathon/Desktop/jsonh/./json.h:1540:29
    #1 0x55b62d10d6db in json_parse_value /home/hyrathon/Desktop/jsonh/./json.h:1949:7
    #2 0x55b62d10c8f0 in json_parse_object /home/hyrathon/Desktop/jsonh/./json.h:1719:5
    #3 0x55b62d10d1c8 in json_parse_value /home/hyrathon/Desktop/jsonh/./json.h:1940:5
    #4 0x55b62d115c85 in json_parse_ex /home/hyrathon/Desktop/jsonh/./json.h:2129:3
    #5 0x55b62d12c192 in main /home/hyrathon/Desktop/jsonh/fuzz.c:29:5
    #6 0x7fb9e4174d8f in __libc_start_call_main csu/../sysdeps/nptl/libc_start_call_main.h:58:16
    #7 0x7fb9e4174e3f in __libc_start_main csu/../csu/libc-start.c:392:3
    #8 0x55b62d03a314 in _start (/home/hyrathon/Desktop/jsonh/san+0x33314) (BuildId: a0e983e1c9c38a8763824dc5481f79d22fe8c82a)

0x613000000189 is located 0 bytes to the right of 329-byte region [0x613000000040,0x613000000189)
allocated by thread T0 here:
    #0 0x55b62d0bd15e in __interceptor_malloc (/home/hyrathon/Desktop/jsonh/san+0xb615e) (BuildId: a0e983e1c9c38a8763824dc5481f79d22fe8c82a)
    #1 0x55b62d114f15 in json_parse_ex /home/hyrathon/Desktop/jsonh/./json.h:2088:18
    #2 0x55b62d12c192 in main /home/hyrathon/Desktop/jsonh/fuzz.c:29:5
    #3 0x7fb9e4174d8f in __libc_start_call_main csu/../sysdeps/nptl/libc_start_call_main.h:58:16

SUMMARY: AddressSanitizer: heap-buffer-overflow /home/hyrathon/Desktop/jsonh/./json.h:1540:29 in json_parse_string
Shadow bytes around the buggy address:
  0x0c267fff7fe0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x0c267fff7ff0: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x0c267fff8000: fa fa fa fa fa fa fa fa 00 00 00 00 00 00 00 00
  0x0c267fff8010: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
  0x0c267fff8020: 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
=>0x0c267fff8030: 00[01]fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c267fff8040: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c267fff8050: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c267fff8060: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c267fff8070: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c267fff8080: 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
==4928==ABORTING


#0  json_parse_string (state=0x7fffffffc700, string=0x613000000158) at ./json.h:1540
#1  0x000055555565a6dc in json_parse_value (state=0x7fffffffc700, is_global_object=0, value=0x613000000130) at ./json.h:1949
#2  0x00005555556598f1 in json_parse_object (state=0x7fffffffc700, is_global_object=1, object=0x613000000068) at ./json.h:1719
#3  0x000055555565a1c9 in json_parse_value (state=0x7fffffffc700, is_global_object=4, value=0x613000000040) at ./json.h:1940
#4  0x0000555555662c86 in json_parse_ex (src=0x7fffffffcb48, src_size=35, flags_bitset=6905944396334922751, alloc_func_ptr=0x0, user_data=0x0, result=0x7fffffffdbc0) at ./json.h:2129
#5  0x0000555555679193 in main (argc=2, argv=0x7fffffffde08) at fuzz.c:29
#6  0x00007ffff7ca3d90 in __libc_start_call_main (main=main@entry=0x555555678e30 <main>, argc=argc@entry=2, argv=argv@entry=0x7fffffffde08) at ../sysdeps/nptl/libc_start_call_main.h:58
#7  0x00007ffff7ca3e40 in __libc_start_main_impl (main=0x555555678e30 <main>, argc=2, argv=0x7fffffffde08, init=<optimized out>, fini=<optimized out>, rtld_fini=<optimized out>, stack_end=0x7fffffffddf8) at ../csu/libc-start.c:392
#8  0x0000555555587315 in _start ()

The input to trigger this bug is attached. The first 8 bytes are the flags for json_parse_ex() and the rest is the content(src). Please use address sanitizer to reproduce the bug, as non-crash overflow is hard to detect or locate without shadow memory.

Also, you can always use the code below to reproduce the vulnerabilities I reported(and I won’t attach it in each report for simplicity:

#include <stdint.h> #include <string.h> #include <stdlib.h> #include <stdio.h> #include “json.h”

#define BUFF_SIZE 0x1000

int main(int argc, char** argv){ if(argc != 2){ printf(“Wrong number of arguments\n”); exit(0); }

char data\[BUFF\_SIZE\];
FILE \*f = fopen(argv\[1\], "r");
size\_t size = fread(data, 1, BUFF\_SIZE, f);

if(size < sizeof(size\_t)){
    // to short input, exit
    exit(0);
}
size\_t flags = \*((size\_t \*)data);

printf("The flags is 0x%zx\\n", flags);

struct json\_parse\_result\_s result;

json\_parse\_ex(data + sizeof(size\_t), size - sizeof(size\_t), flags, NULL, NULL, &result);

}