Over the past few years IIS has been the most maligned Web server out there. Whether it's popularity has made it an easy target or if it does have some basic weaknesses, there are still some things you should be aware of.
If you are using Internet Information Server, here are seven key security tips you need to know:
- The IUSR_<servername> account is just as well-known as the administrator account. If someone can learn your Web server's name, they also know the default Web user account. You should rename this account, but be sure to duplicate the changes both in Active Directory Users and Computers and the IIS Web and FTP services Properties.
- The IUSR account is a member of the Everyone & Authenticated Users groups. The IUSR account has the Access this computer from the network and Log on locally User Rights. So, specifically deny access for the IUSR account on everything, then grant the IUSR account access only where needed.
- The IUSR account is authenticated automatically, so all anonymous Web and FTP users are logging in even if they don't know it.
- Avoid using common filenames and directory structures; i.e., don't use wwwroot, ftproot, or iispub since these are well-known. Using unique folder names will thwart many types of attacks that require a known directory path to function. Also, avoid using virtual directories or creating aliases to folders on other systems. If your directory structure is ever compromised,
- links to other systems will become vulnerable.
- Avoid deploying Web services on domain controllers, file servers and other servers that host sensitive and confidential data.
- When hosting internal or private Web services, use an alternate TCP port to make its discovery that much more difficult for those who are not authorized.
- Never use any script or programming component on a production IIS system until it has been thoroughly tested. For example, if an ISAPI scripts uses the RevertToSelf(); command, it can grant Web surfers system level privileges.
James Michael Stewart is a researcher and writer for Lanwrights, Inc.
This was first published in April 2002