Source: https://code.google.com/p/google-security-research/issues/detail?id=526
Fuzzing of packed executables found the attached crash.
0:022> g
(83c.bbc): Access violation - code c0000005 (first chance)
First chance exceptions are reported before any exception handling.
This exception may be expected and handled.
eax=00000005 ebx=04320481 ecx=7ffffffd edx=f50139ce esi=80000027 edi=0432005c
eip=15de0bd2 esp=0bb4ee04 ebp=0bb4ee20 iopl=0 ov up ei pl nz na pe nc
cs=0023 ss=002b ds=002b es=002b fs=0053 gs=002b efl=00010a06
15de0bd2 8a843700040000 mov al,byte ptr [edi+esi+400h] ds:002b:84320483=??
If I step through that address calculation:
0:022> p
eax=00000005 ebx=04320481 ecx=7ffffffd edx=f50139ce esi=80000022 edi=0432005c
eip=15de0d3a esp=0bb4ee04 ebp=0bb4ee20 iopl=0 nv up ei pl zr na pe nc
cs=0023 ss=002b ds=002b es=002b fs=0053 gs=002b efl=00000246
15de0d3a 03f0 add esi,eax
0:022> p
eax=00000005 ebx=04320481 ecx=7ffffffd edx=f50139ce esi=80000027 edi=0432005c
eip=15de0d3c esp=0bb4ee04 ebp=0bb4ee20 iopl=0 nv up ei ng nz na pe nc
cs=0023 ss=002b ds=002b es=002b fs=0053 gs=002b efl=00000286
15de0d3c 3b75f0 cmp esi,dword ptr [ebp-10h] ss:002b:0bb4ee10=000003f1
0:022> p
eax=00000005 ebx=04320481 ecx=7ffffffd edx=f50139ce esi=80000027 edi=0432005c
eip=15de0d3f esp=0bb4ee04 ebp=0bb4ee20 iopl=0 ov up ei pl nz na pe nc
cs=0023 ss=002b ds=002b es=002b fs=0053 gs=002b efl=00000a06
15de0d3f 0f8c8dfeffff jl 15de0bd2 [br=1]
0:022> p
eax=00000005 ebx=04320481 ecx=7ffffffd edx=f50139ce esi=80000027 edi=0432005c
eip=15de0bd2 esp=0bb4ee04 ebp=0bb4ee20 iopl=0 ov up ei pl nz na pe nc
cs=0023 ss=002b ds=002b es=002b fs=0053 gs=002b efl=00000a06
15de0bd2 8a843700040000 mov al,byte ptr [edi+esi+400h] ds:002b:84320483=??
This looks like an integer overflow:
int base;
int index;
if (base + index > argMaxSize)
goto error;
Because it's a signed comparison, 7ffffffd + 5 is
0:022> ? ecx + eax
Evaluate expression: -2147483646
Which is less than 0x3f1, the size parameter. Those values are directly from the executable being scanned.
Proof of Concept:
https://gitlab.com/exploit-database/exploitdb-bin-sploits/-/raw/main/bin-sploits/38283.zip
