AusCERT - AU-2005.0023 -- AusCERT Update - [Win] - Partial workarounds available for WMF file handling vulnerability

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AU-2005.0023 -- AusCERT Update - [Win] - Partial workarounds available for WMF file handling vulnerability
Date: 30 December 2005
References: AL-2005.0043 AU-2006.0001

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AusCERT Update AU-2005.0023 - [Win]
Partial workarounds available for WMF file handling vulnerability
30 December 2005

        AusCERT Update Summary
        ----------------------

Operating System:  Windows XP SP2 and prior
                   Windows 2000 SP4 and prior
                   Windows Server 2003 SP1 and prior
                   Windows 98
                   Windows ME
Impact:            Execute Arbitrary Code/Commands
Access:            Remote/Unauthenticated
CVE Names:         CVE-2005-4560

Ref:               AL-2005.0043


OVERVIEW:

	Microsoft Security Advisory 912840 has been released [1] confirming 
	the WMF file handling vulnerability reported yesterday in AusCERT 
	Alert AL-2005.0043.[2] The Microsoft advisory provides further details 
	on the vulnerability and affected systems, however a software update 
	fixing this vulnerability is not available as yet. 

	Partial workarounds can be used to mitigate the risk to some extent
	and these are described below.

	This vulnerability continues to be actively exploited. Computers can 
	be compromised by visiting a malicious web page using Microsoft 
	Internet Explorer, or potentially by viewing an email in an HTML 
	email client such as Outlook.

	Note that exploitation may also occur if the Windows Explorer is used 
	to simply view a directory containing a malicious file, without 
	actually opening the file.


IMPACT: (revised)

	Exploitation of this vulnerability allows an attacker to execute 
	arbitrary code with the privileges of the user handling the malicious
	file or web page.


MITIGATION:

	No comprehensive solution is yet available. System administrators
	may consider using some of the partial workarounds below until an 
	update is released:

	1. Deregister the vulnerable library SHIMGVW.DLL, using the command:
	   regsvr32 -u %windir%\system32\shimgvw.dll

	   Note: while this addresses the DLL targeted by the current public
	   exploit code, it is possible that the computer may still be 
	   vulnerable as it has been suggested that GDI32.DLL may also be 
	   affected.[3] This has not yet been officially confirmed by the 
	   vendor. 

	2. On Windows XP with Service Pack 2, configure DEP (Data Execution 
	   Prevention) to apply to all programs, rather than just essential
	   Windows components. Instructions for doing this are provided in [4].
	   Note: This DEP setting may impact compatibility with some software.

	3. Configure email clients to view email as "plain text only" rather
	   than HTML. 

	4. Snort signatures are available to detect bytes generated by the 
	   current public exploit.[5] Note that this may not detect modified
	   exploits, or exploit data contained within an encrypted or 
	   compressed data stream.
	
	5. As always, users should avoid clicking on any links in emails, 
	   unless the email was already expected beforehand.


REFERENCES:

	[1] Microsoft Security Advisory 912840
	    http://www.microsoft.com/technet/security/advisory/912840.mspx

	[2] AusCERT Alert AL-2005.0043
	    http://www.auscert.org.au/5872

	[3] US-CERT Vulnerability Note VU#181038
	    http://www.kb.cert.org/vuls/id/181038

	[4] How to Configure Memory Protection in Windows XP SP2
	    http://www.microsoft.com/technet/security/prodtech/windowsxp/depcnfxp.mspx

	[5] SANS Handler Diary December 29th 2005
	    http://isc.sans.org/diary.php?storyid=978


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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