Another Tuesday, another round of security bulletins from Microsoft. Are you patched? Nessus contains credentialed local checks for all security bulletins, and a network-based uncredentialed check for MS09-064.
Severity is a Matter of Perspective
What struck me as interesting this month are the severity ratings. Microsoft publishes these ratings as a guide to help customers evaluate the vulnerability risk. In many cases, they seem to be doing their customers a disservice. For example, a remotely exploitable vulnerability in Microsoft Word or Excel could be leveraged by attackers to compromise desktop systems. These types of vulnerabilities are frequently exploited by attackers and penetration testers alike to gain access to sensitive information. The advice I always give to organizations is to evaluate each vulnerability with respect to how it affects your business, not what has been published by the vendor.
In addition, if the evaluation of severity is coming from a vendor, it should adhere to some industry accepted standard calculation, such as the CVSS score. Nessus plugins use this scale (1-10, with 10 being the most severe) as a rating for the severity of the vulnerability. While Microsoft rates MS09-067 (a vulnerability in which arbitrary code can be executed as a result of opening an Excel file) as important, Nessus gives it a CVSS score of 9.3. Use these ratings as a guide to develop your patching strategy. For example, if you heavily use Excel, you will need to patch right away. If you do not use Excel, then it is not as critical to patch. You could employ a temporary solution for mitigation by blocking incoming Excel file attachments while you focus on vulnerabilities that pose a bigger risk.
Patch Tuesday Breakdown & Thoughts
What follows is a breakdown of the patches that have been released by Microsoft in the latest "Patch Tuesday" set and the associated Nessus plugins:
- MS09-063 - Nessus Plugin ID 42437 (Credentialed Check) - This is an interesting vulnerability in a networking protocol called Web Services on Devices API (WSDAPI). More information http://msdn.microsoft.com/en-us/library/aa385800(VS.85).aspx. Essentially it allows clients to find devices on the network. If you really want to dig deep into this protocol check out http://blogs.msdn.com/dandris/archive/2007/11/09/wsdapi-101-part-1-web-services-from-10-000-feet.aspx
- MS09-064 - Nessus Plugin ID 42438 (Credentialed Check) & Nessus Plugin ID 42443 (Uncredentialed Check) - This patch only affects Windows 2000 Servers. If you are running this operating system, you need to upgrade. Now, that’s easy for me to say, but much harder to implement in your environment. If I look at the penetration tests I've done over the years there is almost always an older Windows NT and/or 2000 system laying around. Usually the excuses are "it’s a test system", "it’s a lab system", "we're retiring that system", or the worst case "it runs some mission critical software provided by a vendor that does not support the recent patches or upgrade to a new operating system".
- MS09-065 - Nessus Plugin ID 42439 (Credentialed Check) - A vulnerability that can be executed by rendering fonts! I would expect that there might be other attack vectors, such as in any program that can display text beyond something in the browser. Since this vulnerability is in the Windows kernel, other vectors such as documents, instant message programs and more could access the vulnerable functions.
- MS09-066 - Nessus Plugin ID 42440 (Credentialed Check) - This vulnerability relates to a denial of service condition in LDAP running on Windows 2003/2008 servers. Typically the servers running this service provide the function of a domain controller, which is essential for authentication to occur in the Windows domain. The ability to cause a denial of service condition on these systems could lead to significant downtime and prove to be quite costly to an organization.
- MS09-067 - Nessus Plugin ID 42441 (Credentialed Check) - A question for Microsoft: why is this vulnerability rated “important” and not “critical”? In case you haven't heard, the way attackers are getting in is via phishing attacks and emailing end users. If you can slip something past the SPAM filter, email anti-virus software and desktop anti-virus software, it is a sure win. That may sound like a lot of "hurdle jumping", but it is much easier than you may think. An attacker is relying on the fact that your organization needs to do business, and part of that process is exchanging documents via email. Thus, certain document types are allowed to pass, and differentiating between the ones that contain exploits and those that do not turns out to be pretty difficult.
- MS09-068 - Nessus Plugin ID 42442 (Credentialed Check) - Same scenario as above, but affects Word.