Source: https://code.google.com/p/google-security-research/issues/detail?id=414&can=1
The following crash was observed in MS Office 2007 running under Windows 2003 x86. Microsoft Office File Validation Add-In is disabled and application verified was enabled for testing and reproduction. This sample did not reproduce in Office 2010 running on Windows 7 x86.
The attached minimized PoC that produces the crash with 2 bit changes from the original file at offsets 0x11E60 and 0x1515F. Standard office document parsers did not reveal any significance about this location.
Attached files:
Fuzzed minimized PoC: 1567070353_min.doc
Fuzzed non-minimized PoC: 1567070353_crash.doc
Original non-fuzzed file: 1567070353_orig.doc
DLL Versions:
mso.dll: 12.0.6721.5000
wwlib.dll: 12.0.6720.5000
Observed Crash:
eax=00000001 ebx=00000004 ecx=0189ff18 edx=00000019 esi=32646a30 edi=0db0eff8
eip=32fbca76 esp=0012bc98 ebp=0012bcb8 iopl=0 nv up ei pl nz na po nc
cs=001b ss=0023 ds=0023 es=0023 fs=003b gs=0000 efl=00010202
32fbca73 8b7df8 mov edi,dword ptr [ebp-8]
=> 32fbca76 f6470201 test byte ptr [edi+2],1 ds:0023:0db0effa=??
32fbca7a 7419 je mso!Ordinal2690+0x476 (32fbca95)
32fbca7c 833e07 cmp dword ptr [esi],7
32fbca7f 7414 je mso!Ordinal2690+0x476 (32fbca95)
32fbca81 8b4508 mov eax,dword ptr [ebp+8]
32fbca84 6a20 push 20h
32fbca86 ff7010 push dword ptr [eax+10h]
32fbca89 8d4dfc lea ecx,[ebp-4]
32fbca8c 51 push ecx
32fbca8d ff10 call dword ptr [eax]
32fbca8f 8127fffffeff and dword ptr [edi],0FFFEFFFFh
Stack Trace:
0:000> kb 8
ChildEBP RetAddr Args to Child
WARNING: Stack unwind information not available. Following frames may be wrong.
0012bcb8 32fbcdc3 0012be28 0d9f4fe8 00000000 mso!Ordinal2690+0x457
0012bccc 32fbce5b 0012be28 0d9f4fe8 0012be28 mso!Ordinal2690+0x7a4
0012bd20 32fbc93e 0012be28 0d9f4fe8 0ddceeb8 mso!Ordinal2690+0x83c
0012bd74 32fbcd73 0012be28 0d9f4fe8 0db2f45a mso!Ordinal2690+0x31f
0012bd94 316dfe8f 0dbe8e38 0012be28 317e9c10 mso!Ordinal2690+0x754
0012bdb0 317e9aa4 0012be08 00000000 00000000 wwlib!wdCommandDispatch+0xcd37
0012bde4 31980e8d 0012be08 000000b4 038b78bc wwlib!wdCommandDispatch+0x11694c
0012c07c 31980b0f 0db2c9c0 00000000 00000001 wwlib!wdCommandDispatch+0x2add35
In this crash the value being dereferenced in edi is free-ed memory:
0:000> !heap -p -a 0xdb0eff8
address 0db0eff8 found in
_DPH_HEAP_ROOT @ 1151000
in free-ed allocation ( DPH_HEAP_BLOCK: VirtAddr VirtSize)
d9e5240: db0e000 2000
7c83e330 ntdll!RtlFreeHeap+0x0000011a
0189fe9c vfbasics!AVrfpRtlFreeHeap+0x000000f8
331039d5 mso!Ordinal1743+0x00002d4d
329c91d1 mso!MsoFreePv+0x0000003f
329c913c mso!Ordinal519+0x00000017
32a54dcc mso!Ordinal320+0x00000021
32bb6f2e mso!Ordinal379+0x00000eae
There is a 1-bit clear at the location specified by edi shortly after the faulting eip location as well making this an exploitable condition.
Proof of Concept:
https://gitlab.com/exploit-database/exploitdb-bin-sploits/-/raw/main/bin-sploits/37913.zip
