N/A - KB930181

Microsoft is aware of published information and proof-of-concept code that attempts to exploit a possible vulnerability in the Client Server Run-Time Subsystem. At this time Microsoft has not seen any indications of active exploitation of the vulnerability. Our initial investigation of the public posting confirms that a local authenticated denial of service is possible on Windows Platforms. Microsoft has activated its emergency response process and is continuing to investigate this public report

Customers in the U.S. and Canada who believe they are affected can receive technical support from Microsoft Product Support Services at 1-866-PCSAFETY. .International customers can receive support from their local Microsoft subsidiaries. There. For more information about how to contact Microsoft for support issues, visit the International Support Web site.

Upon completion of this investigation, Microsoft will take the appropriate action to help protect our customers. This may include providing a security update through our monthly release process or providing an out-of-cycle security update, depending on customer needs.

Mitigating Factors:

An attacker must have valid logon credentials and be able to log on locally to exploit this vulnerability locally.

Workarounds:

No workarounds have been identified for this vulnerability.

What is the scope of the advisory?
Microsoft is aware of public posting of exploit code targeting a possible vulnerability in the Client Server Run-Time Subsystem. This affects the software that is listed in the “Overview” section

Is this a security vulnerability that requires Microsoft to issue a security update?
Microsoft is still investigating this issue. Upon completion of this investigation, Microsoft will take the appropriate action to help protect our customers. This may include providing a security update.

How could an attacker exploit the vulnerability?
To exploit this vulnerability, an attacker would first have to log on to the system. An attacker could then run a specially crafted application that could exploit the vulnerability and cause the system to stop responding resulting in a reboot.

What is the Client Server Run-Time Subsystem?
Csrss is the user-mode portion of the Win32 subsystem (with Win32.sys being the kernel-mode portion). Csrss stands for client/server run-time subsystem and is an essential subsystem that must be running at all times. Csrss is responsible for console windows, creating and/or deleting threads.

How does this issue relate to the vulnerability that is corrected by MS06-075?
While both issues deal with Client Server Run-Time Subsystem, the published proof of concept code affects a potential new vulnerability that was not addressed as part of MS06-075. MS06-075 helps protect against the vulnerability that is discussed in that bulletin, but does not address this new potential vulnerability.