Microsoft Windows contains a vulnerability that could allow an unauthenticated, remote attacker to cause a denial of service (DoS) condition.
The vulnerability is due to errors in handling malformed TCP/IP packets with small or zero size TCP receive window size. An unauthenticated, remote attacker could exploit the vulnerability by sending a series of malicious network packets to the vulnerable host. If successful, the attacker could exhaust available connections, resulting in a DoS condition.
Microsoft has confirmed this vulnerability in a security bulletin and released software updates that correct it.
Indicators of Compromise
Systems running the following versions of Microsoft Windows are vulnerable:
Windows 2000 SP4 and prior Windows XP SP3 and prior Windows XP Professional x64 Edition SP2 and prior
Windows Server 2003 SP2 and prior
Windows Server 2003 x64 Edition SP2 and prior
Windows Vista SP2 and prior
Windows Vista x64 Edition SP2 and prior
Windows Server 2008 for 32-bit Systems SP2 and prior
Windows Server 2008 for x64-based Systems SP2 and prior
Windows Server 2008 for Itanium-based Systems SP2 and prior
This vulnerability is due to errors in handling malformed TCP/IP packets with small or zero size TCP receive window size. The processing of a malformed packet could cause the Windows TCP stack to continue to wait for network transmissions. In the event of a malicious packet, no further communication may occur, causing the connection to wait indefinitely in a FIN-WAIT-1 or FIN-WAIT-2 status. A series of malicious packets could cause the system to keep all available connections in a waiting state, preventing the establishment of other connections.
An unauthenticated, remote attacker could exploit this vulnerability by sending a malicious network packet to a vulnerable system. When processed, the packet could cause the system to leave a TCP/IP connection in a waiting state. By sending a series of malicious packets, an attacker could cause the system to exhaust its available connections, resulting in a DoS condition.
To exploit the vulnerability, an attacker must be able to send a series of malicious TCP/IP packets to a vulnerable host. Systems connected to the Internet are most at risk. Network filtering devices may flag these packets, because they have very small or zero window sizes, allowing administrators to identify ongoing attacks.
Although Microsoft has confirmed this vulnerability in Windows 2000 and Windows XP, updates for these operating systems will not be released.
An exploit could allow the attacker to exhaust the available TCP/IP connections on a targeted system, preventing the system from establishing additional networks connections. As a result, authorized users could not gain access to resources on the system. Sessions already established prior to an attack may persist, allowing some services to remain available.
Administrators are advised to apply the appropriate updates.
Administrators are advised to restrict network access to affected systems.
Administrators may consider using the Microsoft Baseline Security Analyzer (MBSA) scan tool to identify common security misconfigurations and missing security updates on system endpoints.
Administrators are advised to monitor critical systems.
Microsoft has re-released a security bulletin at the following link: MS09-048
Microsoft customers can obtain updates directly by using the links in the security bulletin. These updates are also distributed by Windows automatic update features and available on the Windows Update website. Microsoft Windows Server Update Services (WSUS), Systems Management Server, and System Center Configuration Manager can assist administrators in deploying software updates.
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