Description

NULL Pointer Dereference in function vim_regexec_string at regexp.c:2733 allows attackers to cause a denial of service (application crash) via a crafted input.

vim version

git log
commit 31ad32a325cc31f0f2bdd530c68bfb856a2187c5 (HEAD -> master, tag: v8.2.4949, origin/master, origin/HEAD)

History

Very similar to what was fixed in 8.2.4901 and 8.2.4938, but another different code path. How about check for NULL regprog right at regexp.c:2733 in function vim_regexec_string?

POC

./vim -u NONE -i NONE -n -m -X -Z -e -s -S /mnt/share/max/fuzz/poc/vim/poc_n3_s.dat -c :qa!
Segmentation fault

poc_n3_s.dat

GDB

─── Output/messages ────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────
[Thread debugging using libthread_db enabled]
Using host libthread_db library "/lib/x86_64-linux-gnu/libthread_db.so.1".

Program received signal SIGSEGV, Segmentation fault.
0x0000000000d24b92 in vim_regexec_string (rmp=0x7fffffff8980, line=0x602000006770 "0", col=0, nl=0) at regexp.c:2733
2733        if (rmp->regprog->re_in_use)
─── Assembly ───────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────
 0x0000000000d24b77  vim_regexec_string+567 cmp    %cl,%al
 0x0000000000d24b79  vim_regexec_string+569 jl     0xd24b8b <vim_regexec_string+587>
 0x0000000000d24b7f  vim_regexec_string+575 mov    0x118(%rbx),%rdi
 0x0000000000d24b86  vim_regexec_string+582 callq  0x4a1350 <__asan_report_load4>
 0x0000000000d24b8b  vim_regexec_string+587 mov    0x118(%rbx),%rax
 0x0000000000d24b92  vim_regexec_string+594 cmpl   $0x0,(%rax)
 0x0000000000d24b95  vim_regexec_string+597 je     0xd24bfc <vim_regexec_string+700>
 0x0000000000d24b9b  vim_regexec_string+603 mov    0x176770c,%ecx
 0x0000000000d24ba2  vim_regexec_string+610 mov    $0x172e1e0,%rax
 0x0000000000d24ba9  vim_regexec_string+617 mov    (%rax),%rax
─── Breakpoints ────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────
─── Expressions ────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────
─── History ────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────
─── Memory ─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────
─── Registers ──────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────
    rax 0x0000000000000014     rbx 0x00007fffffff8660     rcx 0x0000000000000000     rdx 0x0000000000000000     rsi 0x0000602000006770        rdi 0x00007fffffff8980
    rbp 0x00007fffffff8860     rsp 0x00007fffffff8560      r8 0x0000000002064a40      r9 0x000000000000e53e     r10 0x000000000000e504        r11 0x000000000000e500
    r12 0x000000000041fe30     r13 0x00007fffffffe3f0     r14 0x0000000000005606     r15 0x0000000000005600     rip 0x0000000000d24b92     eflags [ PF ZF IF RF ]
     cs 0x00000033              ss 0x0000002b              ds 0x00000000              es 0x00000000              fs 0x00000000                 gs 0x00000000
─── Source ─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────
 2728      int        result;
 2729      regexec_T    rex_save;
 2730      int        rex_in_use_save = rex_in_use;
 2731
 2732      // Cannot use the same prog recursively, it contains state.
 2733      if (rmp->regprog->re_in_use)
 2734      {
 2735      emsg(_(e_cannot_use_pattern_recursively));
 2736      return FALSE;
 2737      }
─── Stack ──────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────
[0] from 0x0000000000d24b92 in vim_regexec_string+594 at regexp.c:2733
[1] from 0x0000000000d2564a in vim_regexec+90 at regexp.c:2816
[2] from 0x000000000053f286 in fname_match+454 at buffer.c:2958
[3] from 0x000000000051af2b in buflist_match+139 at buffer.c:2934
[4] from 0x0000000000515845 in buflist_findpat+4053 at buffer.c:2656
[5] from 0x00000000007f821e in do_one_cmd+50910 at ex_docmd.c:2532
[6] from 0x00000000007e5826 in do_cmdline+14134 at ex_docmd.c:992
[7] from 0x0000000000e8c39d in do_source_ext+13725 at scriptfile.c:1674
[8] from 0x0000000000e88df7 in do_source+103 at scriptfile.c:1801
[9] from 0x0000000000e8872d in cmd_source+2317 at scriptfile.c:1174
[+]
─── Threads ────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────
[1] id 3841802 name vim from 0x0000000000d24b92 in vim_regexec_string+594 at regexp.c:2733
─── Variables ──────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────
arg rmp = 0x7fffffff8980: {regprog = 0x0,startp = {[0] = 0x7fffffff8d08 "\025", [1] = 0x6110000007d1 …, line = 0x602000006770 "0": 48 '0', col = 0, nl = 0
loc result = -1, rex_save = {reg_match = 0x7fffffff7840,reg_mmatch = 0x7fffffff7860,reg_startp = 0x7fffffff7880,reg_endp = 0x430…, rex_in_use_save = 0
────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────
>>> p rmp->regprog
$1 = (regprog_T *) 0x0
>>>

Impact

NULL Pointer Dereference in function vim_regexec_string allows attackers to cause a denial of service (application crash) via a crafted input.