[SecurityArchitect-009]: Microsoft Windows Mobile Double Free Vulnerability

Vendor: Microsoft

Product: Windows Mobile

Vulnerability: Double Free

Tested vulnerable versions: Windows Mobile 6.1 and 6.5

Tested on : HTC Touch (WM 6.1), HTC Touch2 (WM 6.5)

CREDITS: Celil Ünüver from SecurityArchitect.Org

CONTACT: celilunuver[n0sp4m]gmail.com

Vulnerability Details and Analysis:

The vulnerability is a double free. It occurs when multiple buffers are allocated
to handle a very large Name (N) field in the vCard (.vcf) file. This file can be
received by MMS or Bluetooth.
After opening the malformed vcf file, it gives an error dialog. Then it frees the
buffers and crashes;

pimutil.dll:

.text:02B73DE0 sub_2B73DE0 ; CODE XREF:
sub_2B74388+1Cp
.text:02B73DE0 STMFD SP!, {R4,LR}
.text:02B73DE4 MOV R4, R0
.text:02B73DE8 LDR R2, [R4,#0xC]
.text:02B73DEC LDR R3, =off_2B66DB8
.text:02B73DF0 CMP R2, #0
.text:02B73DF4 LDRNE R0, [R4,#8]
.text:02B73DF8 STR R3, [R4]
.text:02B73DFC BLNE sub_2BA6350
.text:02B73E00 LDR R0, [R4,#8]
.text:02B73E04 BL sub_2BA56F8 ; sysfreestrng()
.text:02B73E08 LDR R0, [R4,#0x14] !
.text:02B73E0C BL sub_2BA56F8 ; sysfreestring
.text:02B73E10 LDR R0, [R4,#0x14] !!!
DOUBLE FREE!!!*
.text:02B73E14 BL sub_2BA56F8 ; sysfreestring
.text:02B73E18 LDR R0, [R4,#8]
.text:02B73E1C BL sub_2BA56F8
.text:02B73E20 LDR R3, =(dword_2B66D30+8)
.text:02B73E24 STR R3, [R4]
.text:02B73E28 LDMFD SP!, {R4,LR}
.text:02B73E2C BX LR

*As you see that the pointer at [R4 + 0x14] is passed to SysFreeString() twice.

text:0271E4C0 SysFreeString ; CODE XREF: sub_271AE68+1Cp
.text:0271E4C0 ; sub_271AE68+24p …
.text:0271E4C0 STMFD SP!, {R4,LR}
.text:0271E4C4 CMP R0, #0
.text:0271E4C8 BEQ loc_271E508
.text:0271E4CC LDR R3, =0x1ECD1B8
.text:0271E4D0 SUB R4, R0, #8
.text:0271E4D4 LDR R0, [R3]
.text:0271E4D8 BL sub_27391B8
.text:0271E4DC CMP R0, #0
.text:0271E4E0 BNE loc_271E4F4
.text:0271E4E4 MOV R0, R4
.text:0271E4E8 BL sub_2739168
.text:0271E4EC LDMFD SP!, {R4,LR}
.text:0271E4F0 BX LR
.text:0271E4F4 ;

.text:0271E4F4
.text:0271E4F4 loc_271E4F4 ; CODE XREF:
SysFreeString+20j
.text:0271E4F4 LDR R3, [R4] ----->CRASH !!
.text:0271E4F8 MOV R1, R4
.text:0271E4FC ADD R3, R3, #0x19
.text:0271E500 BIC R2, R3, #0xF
.text:0271E504 BL sub_27295BC
.text:0271E508

*The code at location 0271E4F4 is attempting to extract the 'size' from the heap
chunk header.

Exploiting:

Double Frees are usually exploitable but in this case it doesnt look simple. The
calls to free() occurs in immediate succession. WinCE supports multi-threading, but
this is an extremely hard case to try… I do not have deep knowledge about WinCE
heap structures. So it may be denial of service but I think it can be possible to
exploit this vulnerability. (impossible is nothing ! :P)

Proof of Concept:

www.securityarchitect.org/exploits/wmpoc.vcf

Vendor-Patch Status:
It's 0day :]
Actually I contacted Microsoft but they said ;
"we fixed this issue on WM 6.5 version and we can not publish a bulletin for it"
But i m sure that it is not fixed on 6.5 version. I've tested it on several devices
which have WM 6.5. Also I've tested it on WM 6.5 Professional Emulator (which can
be downloaded from MS Pages) , it crashes too…

Original Advisory:
http://www.securityarchitect.org/advisories/securityarchitect-009.txt

Last Words:
We are not dead , just busy !

Greets to: SecurityArchitect Members (Ulascan) , Hellcode, murderkey …

Links:
www.securityarchitect.org
blog . securityarchitect . org