Abysssec Research
1) Advisory information
Title : GDI+ CreateDashedPath Integer overflow in
gdiplus.dll
Discovery : Nicolas july from vupen
Analysis : Abysssec.com
Vendor : http://www.microsoft.com
Impact : High
Contact : info [at] abysssec.com
Twitter : @abysssec
CVE : CVE-2011-0041
2) Vulnerable version
Gdiplus.dll 5.2.6001.22319
3) Vulnerability information
Class
1-Integer overflow
Impact
Successfully exploiting this issue allows remote attackers to execute
arbitrary code in the context of vulnerable application or cause
denial-of-service conditions.
Remotely Exploitable
Yes
Locally Exploitable
Yes
4) Vulnerabilities detail
The vulnerability exists in gdiplus!GpPath::CreateDashedPath function of
gdiplus.dll that is responsible for bitmap drawing and other 2d graphic
rendering.
EMF+ file is one of the image file format that is rendered by the
library. And the vulnerability is based on some floating point
calculation of an EMF+ path object.
We made the following proof of concept to trigger the issues and it will
be explained more:
A little taste of file format we simply put a EMF_COMMENT record (id =
0x00000046) and embed and emf+ geraphic object ( id = 0x00004008 ) .
For simplicity we ripped out a valid graphic object from another file
and started to play with it. The record have two important area that we
highlighted them in the above picture.
Here is the faulty code:
.text:4ECFCBAD loc_4ECFCBAD:
.text:4ECFCBAD mov eax, esi
.text:4ECFCBAF shl eax, 3
.text:4ECFCBB2 cmp [ebp+lpMem], 0
.text:4ECFCBB6 push eax ; dwBytes
.text:4ECFCBB7 jz short loc_4ECFCBCE
.text:4ECFCBB9 push [ebp+lpMem] ; lpMem
.text:4ECFCBBC call GpRealloc(x,x)
.text:4ECFCBC1 test eax, eax
.text:4ECFCBC3 jz loc_4ECFCCDB
.text:4ECFCBC9 mov [ebp+lpMem], eax
.text:4ECFCBCC jmp short loc_4ECFCBDE
.text:4ECFCBCE ;
---------------------------------------------------------------------------
.text:4ECFCBCE
.text:4ECFCBCE loc_4ECFCBCE:
.text:4ECFCBCE call GpMalloc(x)
.text:4ECFCBD3 test eax, eax
.text:4ECFCBD5 mov [ebp+lpMem], eax
.text:4ECFCBD8 jz loc_4ECFCCDB
The above code uses the eax register as arguments to the GpMalloc
function. GpMalloc is simply a gdi version of heapAlloc function. The
value of eax register is based on various floating point calculation
that is not simple to examine at first look.But I traced the value of
eax register and it seems the calculations are based on our values
mentioned earlear in the file.
And it doesn�t bound checked well, by changing the path value tricky it
is possible when the �shr eax, 3� instruction multiply the value by 8
we get an integer overflow and in turn a faulty heap allocation.
I dynamically traced the values with my proof of concept file. Eax
register is equall to eax + [ebp-38] * 10 and as there are a lot of
values and calculations before that, for better consideration
I made the following diagram:
It took a lot of time explanation of all of the variables above but, the
important one is the GpPath object that is in the code a clone of the
object is made to later be manipulated for drawings.
.text:4ECFC9D9 loc_4ECFC9D9: ; CODE XREF:
GpPath::CreateDashedPath(DpPen const *,GpMatrix const
*,float,float,float,int)+1AAj
.text:4ECFC9D9 fld dword ptr [esi+eax*4]
.text:4ECFC9DC fmul [ebp+arg_0]
.text:4ECFC9DF fstp dword ptr [esi+eax*4]
.text:4ECFC9E2 inc eax
.text:4ECFC9E3 cmp eax, [ebp+arg_4]
.text:4ECFC9E6 jl short loc_4ECFC9D9
.text:4ECFC9E8
.text:4ECFC9E8 loc_4ECFC9E8:
.text:4ECFC9E8 mov ecx, [ebp+var_18] ; Src
.text:4ECFC9EB call GpPath::Clone(void)
.text:4ECFC9F0 mov edi, eax
.text:4ECFC9F2 test edi, edi
.text:4ECFC9F4 jz loc_4ECFCDBA
.text:4ECFC9FA mov eax, [edi]
.text:4ECFC9FC mov ecx, edi
.text:4ECFC9FE call dword ptr [eax+4]
After calling the clone, it checks whether it is a valid clone or not at
address 4ECFC9FE.
The offset +34h of the object contains a pointer to our 4byte path
object values.
0:000> dd ecx
0e03ca50 4ec67e58 68745031 00000000 00000000
0e03ca60 0e03ca74 0e03ca74 00000010 00000010
0e03ca70 00000002 00000100 00000000 00000000
0e03ca80 00000000 0e03ca98 0e03ca98 00000010
0e03ca90 00000010 00000002 449a8eab 458ac500
0e03caa0 449a8eab 4e0000fe 00000000 00000000
0e03cab0 00000000 00000000 00000000 00000000
0e03cac0 00000000 00000000 00000000 00000000
Our floating point values in the file format:
0e03ca98 449a8eab 458ac500 449a8eab 4e0000fe
0e03caa8 00000000 00000000 00000000 00000000
But there are some modifications on our values before we get the faulty
code. First after the clone is performed GpPath::Flatten function made
some changes
to our values based on a transform matrix in the file. So this is cause
of the highlighted 6 DWORDs in the file.���
.text:4ECFC9FE call dword ptr [eax+4]
.text:4ECFCA01 test eax, eax
.text:4ECFCA03 jz loc_4ECFCDBA
.text:4ECFCA09 fld ds:flt_4ECB80FC
.text:4ECFCA0F push ecx ; float
.text:4ECFCA10 lea eax, [ebp+var_F8]
.text:4ECFCA16 fstp [esp+108h+var_108]
.text:4ECFCA19 push eax ; int
.text:4ECFCA1A mov ecx, edi
.text:4ECFCA1C call GpPath::Flatten(GpMatrix const
*,float)
.text:4ECFCA21 cmp [ebp+var_2C], 0
Flattened GpPath object values:
0:000> dd poi(edi+34)
0e03cd18 449a7eab 458ac100 449a7eab 4e0000fd
0e03cd28 00000000 00000000 00000000 00000000
And after that our changed GpPath object is sent to
calculateGradiantArray and some array of floating point values are made
based on its calculation.
There are many other default floating point values has effects on the
value of the overflowing size for GpMalloc that are not so interesting
and I�ve just shown them on the diagram.
After the calculation integer wrapped, the heap allocated by the
gpMalloc function is not big enough to hold our data. So in next uses of
the wrapped allocated heap the corruption occurs.
But it seems there is not a straight way of exploiting such heap
corruptions using a standalone file. .
feel free to contact us at : info [at] abysssec.com
PoC link : http://abysssec.com/files/GDI_PoC.zip
PoC Mirror : https://gitlab.com/exploit-database/exploitdb-bin-sploits/-/raw/main/bin-sploits/17544.zip (GDI_PoC.zip)
