Neowin.net

Date: 30 October 2002
Software: Internet Information Service (IIS)
Impact: Four vulnerabilities, the most serious of which could enable applications on a server to gain system-level privileges.
Max Risk: Moderate

This patch is a cumulative patch that includes the functionality of all security patches released for IIS 4.0 since Windows NT 4.0 Service Pack 6a, and all security patches released to date for IIS 5.0 and 5.1. A complete listing of the patches superseded by this patch is provided below, in the section titled "Additional information about this patch". Before applying the patch, system administrators should take note of the caveats discussed in the same section.

Download: Cumulative patch for IIS 4.0
Download: Cumulative Patch for IIS 5.0
Download: Cumulative Patch for IIS 5.1 32-bit
Download: Cumulative Patch for IIS 5.1 64-bit

In addition to including previously released security patches, this patch also includes fixes for the following newly discovered security vulnerabilities affecting IIS 4.0, 5.0 and/or 5.1:

- A privilege elevation vulnerability affecting the way ISAPIs
are launched when an IIS 4.0, 5.0 or 5.1 server is configured
to run them out of process. By design, the hosting process
(dllhost.exe) should run only in the security context of the
IWAM_computername account; however, it can actually be made to
acquire LocalSystem privileges under certain circumstances,
thereby enabling an ISAPI to do likewise.

- A denial of service vulnerability that results because of a flaw
in the way IIS 5.0 and 5.1 allocate memory for WebDAV requests.
If a WebDAV request were malformed in a particular way, IIS would
allocate an extremely large amount of memory on the server. By
sending several such requests, an attacker could cause the server
to fail.

- A vulnerability involving the operation of the script source
access permission in IIS 5.0. This permission operates in
addition to the normal read/write permissions for a virtual
directory, and regulates whether scripts, .ASP files and
executable file types can be uploaded to a write-enabled virtual
directory. A typographical error in the table that defines the
file types subject to this permission has the effect of omitting
.COM files from the list of files subject to the permission. As a
result, a user would need only write access to upload such a file.

- A pair of Cross-Site Scripting (CSS) vulnerabilities affecting
IIS 4.0, 5.0 and 5.1, and involving administrative web page. Each
of these vulnerabilities have the same scope and effect: an
attacker who was able to lure a user into clicking a link on his
web site could relay a request containing script to a third-party
web site running IIS, thereby causing the third-party site's
response (still including the script) to be sent to the user.
The script would then render using the security settings of
the third-party site rather than the attacker's.

In addition, the patch causes 5.0 and 5.1 to change how frequently the socket backlog list - which, when all connections on a server are allocated, holds the list of pending connection requests - is purged. The patch changes IIS to purge the list more frequently in order to make it more resilient to flooding attacks. The backlog monitoring feature is not present in IIS 4.0.