IIS FTP Service Buffer Overflow Vulnerability

Severity: High

8 February, 2011


  • This vulnerability affects: The IIS FTP service running on Windows Vista, 2008, 7, and 2008 R2
  • How an attacker exploits it: By sending a specially crafted FTP command
  • Impact: In the worst case, an attacker gains complete control of your IIS server
  • What to do: Deploy the appropriate IIS update immediately, or let Windows Automatic Update do it for you


Internet Information Services (IIS) is the popular web and ftp server that ships with all server versions of Windows.

In a security bulletin released today as part of Patch Day, Microsoft describes a serious vulnerability that affects the optional FTP server that comes with the latest versions of IIS. Specifically, the IIS FTP service suffers from a buffer overflow vulnerability involving the way it handles a specially crafted FTP commands (or more specifically, specially encoded characters in an FTP response). By sending such a malformed FTP command, an attacker could exploit this vulnerability to either put your FTP server into a Denial of Service (DoS) state, or to gain complete control of it. An attacker does not have to authenticate to your FTP server to launch this attack.

However, IIS does not install or start the IIS FTP service by default. You are only vulnerable to this attack if you have specifically installed and started this service. That said, many administrators do enable IIS’s FTP service in order to give web administrators an easy way to update their web sites. If you are one of those administrators, you should consider this flaw a serious risk.

Researchers have already publicly released Proof-of-Concept (PoC) exploit code demonstrating the DoS version of this flaw. Whether or not you are using the IIS FTP service, we still recommend you download, test and install this update as soon as you can. Being a critical server update, we highly recommend you test it on non-production servers before pushing it to your real web site.

Solution Path:

Download, test, and deploy the appropriate IIS patches immediately, or let Windows Automatic Update do it for you.

For All WatchGuard Users:

This attack leverages seemingly normal FTP response 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.

What did you think of this alert? Let us know at your.opinion.matters@watchguard.com.

More alerts and articles: Log into the LiveSecurity Archive.

About Corey Nachreiner

Corey Nachreiner has been with WatchGuard since 1999 and has since written more than a thousand concise security alerts and easily-understood educational articles for WatchGuard users. His security training videos have generated hundreds of letters of praise from thankful customers and accumulated more than 100,000 views on YouTube and Google Video. A Certified Information Systems Security Professional (CISSP), Corey speaks internationally and is often quoted by other online sources, including C|NET, eWeek, and Slashdot. Corey enjoys "modding" any technical gizmo he can get his hands on, and considers himself a hacker in the old sense of the word.


  1. IIS FTP Service Buffer Overflow Vulnerability | microreksa - February 8, 2011

    […] IIS FTP Service Buffer Overflow Vulnerability Posted on February 9, 2011 by microreksa IIS FTP Service Buffer Overflow Vulnerability […]

  2. Tweets that mention IIS FTP Service Buffer Overflow Vulnerability « WatchGuard Security Center -- Topsy.com - February 9, 2011

    […] This post was mentioned on Twitter by Wayne Murphy and Akshay Kumar Sharma, WatchGuard Tech. WatchGuard Tech said: Security Alert: IIS FTP Service Buffer Overflow Vulnerability http://ow.ly/1bfkpr […]

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