Microsoft has re-released a security bulletin and updated software to address the SMTP Server malformed MX DNS record denial of service vulnerability.
Microsoft Windows contains a vulnerability within the SMTP service that could allow an unauthenticated, remote attacker to cause a denial of service (DoS) condition.
The vulnerability exists due to a failure to properly validate the contents of a DNS Mail Exchanger (MX) record. An unauthenticated, remote attacker could exploit this vulnerability through an e-mail message designed to cause an affected system to perform a DNS request that triggers a response from an attacker-controlled DNS server. A successful attack could cause a DoS condition and stop the inbound and outbound flow of e-mail.
Microsoft has confirmed this vulnerability in a security bulletin and released updated software.
Systems running the following versions of Microsoft products are affected:
Windows 2000 SP4
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 Server 2003 Itanium 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 R2 for x64-based Systems
Exchange Server 2003 SP2 and prior
An attacker could exploit this vulnerability to trigger a DoS condition by sending an e-mail message to a system running the affected SMTP component. This would require the attacker to host a malicious DNS server that is authoritative for the domain from which the e-mail appears to originate. When the affected system attempts to process the MX record for the malicious domain, an error occurs that congests the SMTP queue and caused the SMTP service to crash.
Systems that utilize an intermediate SMTP SmartHost are unlikely to be affected, as these systems do not look up the domain name of the domain to which an e-mail is sent. In such cases, the step that causes the issue is performed by the intermediary system.
Microsoft has re-released a security bulletin at the following link: MS10-024
An unauthenticated, remote attacker could cause a DoS condition on the SMTP service of an affected system.
The vulnerability exists due to insufficient validation of DNS MX records. An unauthenticated, remote attacker could trigger this issue by sending a message to an affected system that is designed to trigger a non-delivery report (NDR) response. As part of sending the NDR, the server will attempt to look up the default mail server of the reply-to or from domain within the e-mail message by requesting an MX record from the authoritative DNS server for the attacker-controlled domain. When the SMTP service attempts to process the malicious response, a DoS condition may occur.
Administrators are advised to apply the appropriate updates.
Administrators may consider utilizing an unaffected SmartHost for both inbound and outbound e-mail to prevent exploitation.
Administrators may consider utilizing an application firewall that is capable of identifying malicious content in both the SMTP and DNS protocols.
Administrators are advised to monitor critical systems.
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.
Cisco Systems Cisco Intrusion Prevention System (IPS) 6.0
Version 1, April 13, 2010, 1:59 PM: Microsoft Windows contains a vulnerability within the SMTP service that could allow an unauthenticated, remote attacker to cause a denial of service condition. Updates are available.
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