[ISecAuditors Security Advisories] Microsoft IIS5 NTLM and Basic authentication bypass

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INTERNET SECURITY AUDITORS ALERT 2006-013

• Original release date: December 15, 2006
• Last revised: May 22, 2007
• Discovered by: Jesus Olmos Gonzalez
• Severity: 5/5
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I. VULNERABILITY

Microsoft IIS5 NTLM and Basic authentication bypass

II. BACKGROUND

Microsoft Internet Information Server Web Server can protect the
private contents with a basic or NTLM authentication.

Many web pages, intranets and extranets rely on Microsoft security.

IISv5 has a "Hit-highlighting" functionality that opens some site
object and highlights some part of it; that has had a transversal
vulnerability in the past. Now it can be used to bypass the IIS
authentication.

This is poorly documented at KnowledgeBase
http://support.microsoft.com/kb/328832, the real impact is detailed above.

III. DESCRIPTION

Any Internet user can access the private web directories and files of
any IISv5 web, by highlighting it with "Hit-highlighting". To use this
functionality the user has to supply the CiWebhitsfile parameter to
the null.htw object.

The null.htw object has to be accessed from a non-existant directory,
for example http://anyiisweb.com/foo/null.htw

It is possible to use null.htw or other object specified at the
CiTemplate template.

IV. PROOF OF CONCEPT

https://anyiis5.com/authBypass/null.htw?CiWebhitsfile=/protectedfile.aspx&CiRestriction=b&CiHiliteType=full
https://anyiis5.com/authBypass/null.htw?CiWebhitsfile=/some/secretfile.txt&CiRestriction=b&CiHiliteType=full

V. BUSINESS IMPACT

The impact depends on the web contents. Attackers could gain access to
all protected documents, and ASP code.

When an attacker accesses a trusted zone, the probability to get
command execution is higher.

VI. SYSTEMS AFFECTED

Internet Information Services Version 5, any Service Pack.

VII. SOLUTION

Protect the files from the NTFS filesystem instead of relying on the
IIS protection.

Microsoft recommends not to use IISv5 and update to IISv6.

VIII. REFERENCES

http://support.microsoft.com/kb/328832

IX. CREDITS

This vulnerability has been discovered and reported
by Jesus Olmos Gonzalez (jolmos (at) isecauditors (dot) com)

X. REVISION HISTORY

December 15, 2006: Initial release
March 19, 2007: Latest revision
March 27, 2007: First notification to the vendor.
Response: under revision.
April 11, 2007: The vendor considers little changes in their KB.
April 12, 2007: We accept it and propose add comments about the
severity of the problem. Rejected by vendor.
May 21, 2007: Published. As the publish information is
considered really not detailed.

XI. DISCLOSURE TIMELINE

December 15, 2006: Vulnerability acquired by
Jesus Olmos Gonzalez (Internet Security Auditors)

XII. LEGAL NOTICES

The information contained within this advisory is supplied "as-is"
with no warranties or guarantees of fitness of use or otherwise.
Internet Security Auditors, S.L. accepts no responsibility for any
damage caused by the use or misuse of this information.