Technical Information

Brief overview of the risk:
This security update resolves a privately reported vulnerability in the Microsoft Windows Client/Server Run-time Subsystem (CSRSS) in Windows XP and Windows Server 2003. This security update is rated Important for all supported editions of these operating systems.
Detailed Information on the risk:

An elevation of privilege vulnerability exists in the way that the Windows Client/Server Run-time Subsystem (CSRSS) terminates a process when a user logs off. An attacker who successfully exploited this vulnerability could run code designed to monitor the actions of a user who subsequently logged on to the system. This could allow the disclosure of sensitive information or access to data on the affected systems that was accessible to the logged-on user. This sensitive data could include the logon credentials of subsequent users, which an attacker might later use for elevation of privilege or to execute code as a different user on the system. Note that this vulnerability would not allow an attacker to execute code or to elevate their user rights directly. It could be used to collect useful information to try to further compromise the affected system. If a user with administrative privileges subsequently logs on to the system, the attacker could run arbitrary code in kernel mode.

Further information on this exploit is available at : MS11-010