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Microsoft IIS ASP Error Page May Disclose System Information in Certain Cases
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SecurityTracker Alert ID: 1014777
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SecurityTracker URL: http://securitytracker.com/id?1014777
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CVE Reference: GENERIC-MAP-NOMATCH
(Links to External Site)
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Date: Aug 23 2005
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Impact: Disclosure of system information, Disclosure of user information
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Exploit Included: Yes
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Version(s): 5.0, 5.1, 6.0
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Description: A vulnerability was reported in Microsoft Internet Information Server (IIS) in the standard ASP error pages. A remote user may be able to obtain system information.
The standard ASP error page code ('[webroot]/IISHelp/common/500-100.asp') does not properly validate HTTP requests. The code trusts
the value of the user-supplied SERVER_NAME parameter to determine whether to display additional error information when an error
is encountered in executing an ASP page.
If the SERVER_NAME parameter is set to 'localhost', the code will display the ASP code
where the error occurred.
A remote user can supply a specially crafted HTTP header to cause the error page to incorrectly determine
the request to have originated from the localhost interface. In this case, if there is an error in the requested ASP page, some
potentially sensitive ASP code may be displayed.
The vendor was notified on January 28, 2005.
Inge Henriksen reported this
vulnerability.
Additional demonstration exploit examples are available at:
http://ingehenriksen.blogspot.com/
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Impact: A remote user may be able to obtain limited portions of ASP code in certain cases.
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Solution: No solution was available at the time of this entry.
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Vendor URL: www.microsoft.com/ (Links to External Site)
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Cause: Authentication error
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Underlying OS: Windows (Any)
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Reported By: inge_eivind.henriksen@chello.no
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Message History:
None.
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Source Message Contents
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Date: 22 Aug 2005 15:23:08 -0000
From: inge_eivind.henriksen@chello.no
Subject: Remote IIS 5.x and IIS 6.0 Server Name Spoof
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** Inge Henriksen Security Advisory - Full Disclosure Proof of Concept at http://ingehenriksen.blogsp
ot.com/ **
It is possible to remotely spoof the "SERVER_NAME" Microsoft® Internet Information Server®
5.0, 5.1 and 6.0 variable by doing a modified
HTTP request. Thus potentially revealing sensitive ASP code through the IIS 500-100.asp error page,
the spoof also opens up a potential
range of exploits in third party web applications and web services.
Technical Description
Microsoft® Internet Information Server® shows sensitive information if the "SERVER_NAME" II
S 5.x server variable is "localhost". If
a ASP page has an error, the code on the fault line in the ASP page is shown in the browser, but onl
y if"SERVER_NAME" IIS server
variable is "localhost". One can spoof the "SERVER_NAME" IIS server variable so
that it shows whatever one want. Other third party
web applications or web services may also be vulnerable if authentication depends on the validity th
is server variable.
The IIS server variable that can be spoofed is the "SERVER_NAME", it can be accessed throug
h request.servervariables("SERVER_NAME")
with ASP, and HttpContext.Current.Request.ServerVariables("SERVER_NAME") with .NET, other
programming languages have other methods
to access this server variable, but are equally vulnerable.
If the HTTP request comes from a remote client, then the server variable "SERVER_NAME" retu
rns the IP address of the web server itself.
If the HTTP request came from the same IP as the web server (thus the request came from the an authe
nticated user browsing from the
web server itself), then request.servervariables("SERVER_NAME") returns "localhost"
. This fact is used as "proof" in web applications
or web services that the person browsing the web server is in fact browsing from the web server itse
lf. The web applications or web
services may use this proof to display an administrative interface to the web browser user if such i
s the case. One exploitable example
is the IIS 5.x 500-100.asp page; the page uses the server variable to determine if to display the co
de where the error occurred.
The technical description of the server variable is "The server's host name, DNS alias, or IP ad
dress as it would appear in self-referencing
URLs", it is therefore often used to determine the IP address of the web server itself in once
code, this opens up for a range of
exploits including cookie-stealing, data redirection, and other URL manipulation issues.
There are many other applications that utilize validity of this server variable, and MSDN holds many
examples for developers that
are easily exploitable with this bug; among the most serious are the Microsoft® .NET Passport SDK ex
amples, any web application or
web service based on these examples are probably vulnerable due to the bug.
Vendor Status: Notified 28. January 2005
Confirmed applications: Microsoft® Internet Information Server® 5.0, Microsoft® Internet Information
Server® 5.1 and Microsoft® Internet
Information Server® 6.0.
Confirmed platforms: Microsoft® Windows® 2000 with SP4, Microsoft® Windows® XP Professional with SP2,
Microsoft® Windows® 2003 with
SP1.
Full Disclosure Proof of Consept at http://ingehenriksen.blogspot.com/
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