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BYTES & WORDS
Symantec warns of local privilege escalation 0Day in Windows. Busted.
(Wednesday, 17 October 2007) Written by Rubén


Securityfocus/bugtraq readers :
The first email sent to bugtraq contains an important ERRATA( duplicated code ).


Symantec researcher Elia Florio has warned, at the company's weblog,of a 0day attack in Windows XP and 2003 that allows unprivileged users to gain SYSTEM privileges via a buggy driver installed by default.

In his/her post, Elia brings us an important clue:"At the moment, it’s still not clear how the driver is used by Windows because this file does not have the typical Microsoft file properties present in other Windows system files". Such a file is not common so looking for this sort of .sys we come across a couple of them. One of those drivers is secdrv.sys, which is developed by Macrovision as part of SafeDisc.
Mario Ballano (48bits.com) and I have been taking a look at the driver and quickly found this interesting piece of code.

.text:00015E2C                 cmp     [ebp+var_10], 0CA002813h
.text:00015E33                 jz      short loc_15E69
As you can see the IOCTL is METHOD_NEITHER which is a potential vulnerability by itself (few drivers are correctly handling this method). Let's see whether this time is different...

.text:00015ED9                 call    dword ptr [eax+10h] ; Internal Dispatcher
.text:00015EDC                 mov     [ebp+var_1C], eax
.text:00015EDF                 cmp     [ebp+var_1C], 0Ah
.text:00015EE3                 jz      short loc_15EFC
.text:00015EE5                 mov     eax, [ebp+arg_4]
.text:00015EE8                 mov     dword ptr [eax], 0C0000001h
.text:00015EEE                 mov     eax, [ebp+arg_4]
.text:00015EF1                 and     dword ptr [eax+4], 0
.text:00015EF5                 mov     eax, 0C0000001h
.text:00015EFA                 jmp     short loc_15F21
.text:00015EFC ; ---------------------------------------------------------------------------
.text:00015EFC
.text:00015EFC loc_15EFC:                              ; CODE XREF: sub_15E12+D1j
.text:00015EFC                 mov     ecx, [ebp+var_4]
.text:00015EFF                 mov     esi, [ebp+var_C]
.text:00015F02                 mov     eax, [ebp+arg_0]
.text:00015F05                 mov     edi, [eax+3Ch]  ; Output Buffer (Irp->UserBuffer)
.text:00015F08                 mov     eax, ecx        ; Inline memcpy
.text:00015F0A                 shr     ecx, 2
.text:00015F0D                 rep movsd
.text:00015F0F                 mov     ecx, eax
.text:00015F11                 and     ecx, 3
.text:00015F14                 rep movsb

No luck. As you can see the buffer supplied by the user is not properly checked so you can overwrite any address you wish, even kernel addresses. The first 4 DWORDs of the input buffer are copied into the output buffer without any further validation. However,there is restriction: InputBuffer[1] should be a fixed value in order to reach this piece of code. No problem. Take a look at the exploit code.

The driver copies bytes into the output buffer but also into the input buffer so both need to be sanitized. I've released a K-plugin for kartoffel that exploits this flaw on Windows XP SP2 and 2003 (32-bit)

Download at http://kartoffel.reversemode.com/downloads.php.(New video added)
This K-plugin can only be used for personal study and research purposes. Do not email me requesting shellcodes, customized exploit or something like that.

Despite there is no patch available, at the momment, we are disclosing this information since an exploit has been caught in the wild so we see no reason to hide information that can be useful for administrators and researchers.

References:

http://www.symantec.com/enterprise/security_response/weblog/2007/10/privilege_escalation_exploit_i.html
http://www.macrovision.com
http://blog.48bits.com/?p=172 (castilian)

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