Microsoft Security Bulletin (MS00-078)
Patch Available for "Web Server Folder Traversal" Vulnerability
Originally posted: October 17, 2000
Microsoft has released a patch that eliminates a security
vulnerability in Microsoft(r) IIS 4.0 and 5.0. The vulnerability
could potentially allow a visitor to a web site to take a wide range
of destructive actions against it, including running programs on it.
This vulnerability is eliminated by the patch that accompanied
Microsoft Security Bulletin MS00-057. Customers who have applied
that patch are already protected against the vulnerability and do not
need to take additional action. Microsoft strongly urges all
customers using IIS 4.0 and 5.0 who have not already done so to apply
the patch immediately.
Frequently asked questions regarding this vulnerability
and the patch can be found at
Due to a canonicalization error in IIS 4.0 and 5.0, a particular type
of malformed URL could be used to access files and folders that lie
anywhere on the logical drive that contains the web folders. This
would potentially enable a malicious user who visited the web site
to gain additional privileges on the machine - specifically, it could
be used to gain privileges commensurate with those of a locally
logged-on user. Gaining these permissions would enable the malicious
user to add, change or delete data, run code already on the server,
or upload new code to the server and run it.
The request would be processed under the security context of the
IUSR_machinename account, which is the anonymous user account for
IIS. Within the web folders, this account has only privileges that
are appropriate for untrusted users. However, it is a member of the
Everyone and Users groups and, as a result, the ability of the
malicious user to access files outside the web folders becomes
particularly significant. By default, these groups have execute
permissions to most operating system commands, and this would give
the malicious user the ability to cause widespread damage. Customers
who have proactively removed the Everyone and Users groups from
permissions on the server, or who are hosting the web folders on a
different drive from the operating system, would be at significantly
less risk from the vulnerability.
Microsoft strongly recommends that all customers running IIS 4.0 or
5.0 immediately apply the patch for this vulnerability. This patch
was originally released in August 2000 as a fix for a completely
different vulnerability (discussed in Microsoft Security Bulletin
MS00-057), and customers who have already applied it do not need to
take any additional action.
Affected Software Versions
- Microsoft IIS 4.0
- Microsoft IIS 5.0
- Microsoft IIS 4.0:
- Microsoft IIS 5.0:
Note: The IIS 4.0 patch can be installed on systems running Windows
NT(r) 4.0 Service Packs 5 and 6a. It will be included in Windows NT
4.0 Service Pack 7. The IIS 5.0 patch can be installed on systems
running either Windows(r) 2000 Gold or Service Pack 1. It will be
included in Windows 2000 Service Pack 2.
Note: The Download Center pages discussed above may, for the next
several days, only reference the "File Permissions Canonicalization"
vulnerability. However, we are updating the pages to state that it
applies to both that vulnerability and this one.
Note: Additional security patches are available at the Microsoft
Please see the following references for more information related to
- Frequently Asked Questions: Microsoft Security Bulletin MS00-078,
- Microsoft Security Bulletin MS00-057, Microsoft Security Bulletin
- Microsoft Knowledge Base article Q276489 discusses this issue and
will be available soon.
- Microsoft TechNet Security web site,
Obtaining Support on this Issue
This is a fully supported patch. Information on contacting Microsoft
Product Support Services is available at
Microsoft thanks Rain Forest Puppy for reporting this issue to us and
working with us to protect customers.
- October 17, 2000: Bulletin Created.
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Last Updated October 17, 2000