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AL-2009.0041 -- [Win] -- Possible authentication bypass vulnerability in IIS6

Date: 27 May 2009
References: AU-2009.0021  

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===========================================================================
A  U  S  C  E  R  T                                           A  L  E  R  T

                       AL-2009.0041 -- AUSCERT ALERT
                                   [Win]
           Possible authentication bypass vulnerability in IIS6
                                27 May 2009

===========================================================================

        AusCERT Alert Summary
        ---------------------

Product:              Microsoft IIS 6
Operating System:     Windows
Impact:               Execute Arbitrary Code/Commands
                      Access Privileged Data
Access:               Remote/Unauthenticated
CVE Names:            CVE-2009-1676

Revision History:     May 27 2009: Summary added
                      May 19 2009: CVE information added
                      May 18 2009: Initial Release

OVERVIEW

        A possible vulnerability in IIS6 has been found that may allow a
        remote attacker to access protected files without a password.

        Active exploitation of this vulnerability has been reported in
        the wild.


IMPACT

        Successful exploitation of this vulnerability may allow an attacker
        to specify any file on the system. This may allow the download of
        otherwise protected files. Specifying an executable file (for
        instance C:\Windows\System32\cmd.exe) may also allow the attacker to
        run arbitrary code.

        The vulnerability can be used to discover the directory structure of
        the affected system and listings of the contents of every directory -
        an attacker would not need existing knowledge of the server to find
        and steal data.


MITIGATION

        There is currently no information from Microsoft concerning this
        vulnerability.

        Current information indicates that only IIS6 is vulnerable - IIS7 is
        not. Disabling WebDAV (which is not on by default in IIS6) will
        mitigate this issue, but may not be possible for sites using
        SharePoint or other WebDAV based technologies.

        Unless the serving of script source is enabled, an attacker cannot
        use this vulnerability to access the contents of ASP scripts.

        The vulnerability requires the use of a 'Translate: f' header in
        the request. Scanning for and blocking such requests may help to
        mitigate against the vulnerability.


REFERENCES

        [1] Security Focus
            http://www.securityfocus.com/bid/34993

AusCERT has made every effort to ensure that the information contained
in this document is accurate.  However, the decision to use the information
described is the responsibility of each user or organisation. The decision to
follow or act on information or advice contained in this security bulletin is
the responsibility of each user or organisation, and should be considered in
accordance with your organisation's site policies and procedures. AusCERT
takes no responsibility for consequences which may arise from following or
acting on information or advice contained in this security bulletin.

If you believe that your computer system has been compromised or attacked in 
any way, we encourage you to let us know by completing the secure National IT 
Incident Reporting Form at:

        http://www.auscert.org.au/render.html?it=3192

===========================================================================
Australian Computer Emergency Response Team
The University of Queensland
Brisbane
Qld 4072

Internet Email: auscert@auscert.org.au
Facsimile:      (07) 3365 7031
Telephone:      (07) 3365 4417 (International: +61 7 3365 4417)
                AusCERT personnel answer during Queensland business hours
                which are GMT+10:00 (AEST).
                On call after hours for member emergencies only.
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