9 August, 2011
- This vulnerability affects: The DNS service that ships with the Server versions of Windows
- How an attacker exploits it: By sending specially crafted DNS queries
- Impact: In the worst case, an attacker gains complete control of your DNS server
- What to do: Deploy the appropriate Windows update immediately, or let Windows Automatic Update do it for you
The Server versions of Windows ships with a DNS Server to allow administrators to offer Domain Name System services on their networks.
In a security bulletin released today as part of Patch Day, Microsoft describes two vulnerabilities that affects the DNS Server that ships with Server versions of Windows. While this is technically a Windows flaw, which we typically include in a combined Windows alert, we feel that it deserves individual attention due to its high severity.
The worst of the two issues is a remote code execution flaw involving the way the DNS server handles specially crafted Naming Authority Pointer (NAPTR) DNS resource records (RR). By sending a specially crafted NAPTR query to your DNS server, and attacker could exploit this vulnerability to gain complete control of your server. However, the attacker would have to own the malicious domain name, and the authoritative DNS server for that domain name, in order for this attack to succeed. Despite this slight mitigating factor, the DNS server vulnerability poses a serious risk to your network. You should patch your Microsoft DNS servers immediately.
The DNS Server also suffers from a less serious Denial of Service (DoS) flaw, which an attacker could exploit to cause your DNS server to stop responding. If an attacker can prevent your users from accessing DNS services, they essentially prevent access to the Internet (by making it difficult for users to find resources by name).
Download, test, and deploy the appropriate DNS server patches immediately, or let Windows Automatic Update do it for you.
- For Windows Server 2003 (w/SP2)
- For Windows Server 2003 x64 (w/SP2)
- For Windows Server 2003 Itanium (w/SP2)
- For Windows Server 2008 (w/SP2)
- For Windows Server 2008 x64 (w/SP2)
- For Windows Server R2 2008 Itanium
For All WatchGuard Users:
This attack leverages seemingly normal DNS traffic. You should apply the updates above.
Microsoft has released patches to fix this vulnerability
This alert was researched and written by Corey Nachreiner, CISSP.
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