Description

Heap-based Buffer Overflow in function utfc_ptr2len at mbyte.c:2145

Vim Version

git log
commit ebfec1c531f32d424bb2aca6e7391ef3bfcbfe20 (HEAD -> master, tag: v9.0.1234, origin/master, origin/HEAD)

Both POCs also apply to v9.0.1262:
git log
commit f2e30d0c448b9754d0d4daa901b51fbbf4c30747 (HEAD -> master, tag: v9.0.1262, origin/master, origin/HEAD)

Proof of Concept

./vim -u NONE -i NONE -n -m -X -Z -e -s -S POC4 -c :qa!
=================================================================
==2677684==ERROR: AddressSanitizer: heap-buffer-overflow on address 0x602000006ed2 at pc 0x55eb9e00811e bp 0x7fff6aa0cb30 sp 0x7fff6aa0cb20
READ of size 1 at 0x602000006ed2 thread T0
    #0 0x55eb9e00811d in utfc_ptr2len /home/limweicheng/Desktop/Fuzz/vim/src/mbyte.c:2145
    #1 0x55eb9e142732 in get_visual_text /home/limweicheng/Desktop/Fuzz/vim/src/normal.c:3678
    #2 0x55eb9e148a2b in nv_zg_zw /home/limweicheng/Desktop/Fuzz/vim/src/normal.c:2613
    #3 0x55eb9e148a2b in nv_zet /home/limweicheng/Desktop/Fuzz/vim/src/normal.c:2990
    #4 0x55eb9e1378c5 in normal_cmd /home/limweicheng/Desktop/Fuzz/vim/src/normal.c:938
    #5 0x55eb9dd79252 in exec_normal /home/limweicheng/Desktop/Fuzz/vim/src/ex_docmd.c:8887
    #6 0x55eb9dd79c11 in exec_normal_cmd /home/limweicheng/Desktop/Fuzz/vim/src/ex_docmd.c:8850
    #7 0x55eb9dd79c11 in ex_normal /home/limweicheng/Desktop/Fuzz/vim/src/ex_docmd.c:8768
    #8 0x55eb9dd92d41 in do_one_cmd /home/limweicheng/Desktop/Fuzz/vim/src/ex_docmd.c:2580
    #9 0x55eb9dd92d41 in do_cmdline /home/limweicheng/Desktop/Fuzz/vim/src/ex_docmd.c:993
    #10 0x55eb9e467315 in do_source_ext /home/limweicheng/Desktop/Fuzz/vim/src/scriptfile.c:1726
    #11 0x55eb9e46dbd0 in do_source /home/limweicheng/Desktop/Fuzz/vim/src/scriptfile.c:1872
    #12 0x55eb9e46dbd0 in cmd_source /home/limweicheng/Desktop/Fuzz/vim/src/scriptfile.c:1217
    #13 0x55eb9dd92d41 in do_one_cmd /home/limweicheng/Desktop/Fuzz/vim/src/ex_docmd.c:2580
    #14 0x55eb9dd92d41 in do_cmdline /home/limweicheng/Desktop/Fuzz/vim/src/ex_docmd.c:993
    #15 0x55eb9eac1b81 in exe_commands /home/limweicheng/Desktop/Fuzz/vim/src/main.c:3146
    #16 0x55eb9eac1b81 in vim_main2 /home/limweicheng/Desktop/Fuzz/vim/src/main.c:782
    #17 0x55eb9d9c98e7 in main /home/limweicheng/Desktop/Fuzz/vim/src/main.c:433
    #18 0x7f58cd15dd8f in __libc_start_call_main ../sysdeps/nptl/libc_start_call_main.h:58
    #19 0x7f58cd15de3f in __libc_start_main_impl ../csu/libc-start.c:392
    #20 0x55eb9d9d0594 in _start (/home/limweicheng/Desktop/Fuzz/vim/src/vim+0x199594)

0x602000006ed2 is located 0 bytes to the right of 2-byte region [0x602000006ed0,0x602000006ed2)
allocated by thread T0 here:
    #0 0x7f58cdbf7867 in __interceptor_malloc ../../../../src/libsanitizer/asan/asan_malloc_linux.cpp:145
    #1 0x55eb9d9d0aea in lalloc /home/limweicheng/Desktop/Fuzz/vim/src/alloc.c:246

SUMMARY: AddressSanitizer: heap-buffer-overflow /home/limweicheng/Desktop/Fuzz/vim/src/mbyte.c:2145 in utfc_ptr2len
Shadow bytes around the buggy address:
  0x0c047fff8d80: fa fa fd fd fa fa fd fa fa fa fd fd fa fa fd fd
  0x0c047fff8d90: fa fa fd fd fa fa fd fd fa fa fd fa fa fa fd fd
  0x0c047fff8da0: fa fa fd fd fa fa fd fd fa fa fd fa fa fa fd fd
  0x0c047fff8db0: fa fa fd fd fa fa fd fd fa fa fd fd fa fa fd fd
  0x0c047fff8dc0: fa fa fd fd fa fa fd fd fa fa fd fa fa fa 01 fa
=>0x0c047fff8dd0: fa fa 00 00 fa fa 01 fa fa fa[02]fa fa fa fd fa
  0x0c047fff8de0: fa fa fd fa fa fa fd fa fa fa fd fa fa fa fd fa
  0x0c047fff8df0: fa fa fd fa fa fa fd fa fa fa fd fa fa fa fd fa
  0x0c047fff8e00: fa fa fd fa fa fa fd fa fa fa fd fa fa fa fd fa
  0x0c047fff8e10: fa fa fd fd fa fa fd fa fa fa fd fa fa fa 07 fa
  0x0c047fff8e20: fa fa 01 fa fa fa 01 fa fa fa 05 fa fa fa 01 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
==2677684==ABORTING

Impact

This vulnerability is capable of crashing software, modify memory, and possible remote execution.