FW: [Unpatched] Shell and Drag'n'Drop vulnerabilities

2004-09-06T00:00:00
ID SECURITYVULNS:DOC:6745
Type securityvulns
Reporter Securityvulns
Modified 2004-09-06T00:00:00

Description

This is a post forwarded from the Unpatched mailing list ( http://www.pivx.com/pivxlabsUnpatched.asp ), a mailing list that receive advance notification of any security research from PivX Labs.

Cheers

Thor


From: Thor Larholm To: unpatched@pivxlabs.com Subject: [Unpatched] Shell and Drag'n'Drop vulnerabilities

Shell and Drag'n'Drop vulnerabilities

In the recent weeks there has been a lot of exploit activity surrounding the Shell URL protocol which has so far resulted in the several exploits and the "Akak" trojan. Joe Stewart wrote an excellent analysis [1] of what the Akak trojan does once it has infected its users, and in this post I will clarify both how the trojan infects a user and how to protect against exploitation of these vulnerabilities.

When visiting the Akak website the PoC from MikX [2] is used to infect the user, barely changed except for pointing at a different EXE. In addition to this, the site links to "index1.html" which in turn tries to use the older and long-patched modal script injection and MHTML Redirect vulnerabilities to plant the file. However, of primary interest is the MikX exploit for which there are currently no vendor supplied patches and which also affects XPSP2.

The premise behind this Drag'n'Drop exploit is two-fold, one is the ability to open a window with local content and the other is the fact that dropping an IMG element will pass its DYNSRC attribute instead of its SRC attribute. Microsoft has repeatedly tried to prevent IE from referencing local content and even went so far as to disallow any navigation requests to the FILE protocol in IE6SP1 from any non-local zones. This was quickly circumvented [3] and as history shows there continues to exist ways to reference local content. The ability to reference local content has been the key component in most IE exploits over the years.

When a request to Shell:startup is requested the standard rules of URL protocols come into play. Internet Explorer determines whether a Shell protocol exist and whether there is an associated URL protocol handler. As with the recent AIM URL protocol handler vulnerability, you can choose to disable all communication to the Shell protocol by implementing a non-existant or empty URL Protocol handler, as demonstrated below.

====== neutershellurl.reg ========== Windows Registry Editor Version 5.00

[HKEY_CLASSES_ROOT\PROTOCOLS\Handler\shell] "CLSID"="{3050F406-98B5-11CF-BB82-00AA00BDCE0B}" ====== neutershellurl.reg ==========

You can find a copy of this file at

http://www.pivx.com/research/freefixes/neutershellurl.reg

The above takes care of any requests that are sent through the standard URL protocol architecture. However, as the Akak trojan shows you can also use the AnchorClick behavior to force IE to reference local content. The AnchorClick behavior circumvents the traditional request handling and in turn renders the local directory by using the Shell.Explorer ActiveX object. This component is designated for use by Windows Explorer and should never be used inside IE. Taking the cue from MSKB #240797 [4] we can killbit this component and prevent it from being used by IE, as demonstrated below

===== neutershellexplorer.reg ====== Windows Registry Editor Version 5.00

[HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Internet Explorer\ActiveX Compatibility\{8856F961-340A-11D0-A96B-00C04FD705A2}] "Compatibility Flags"=dword:00000400 ===== neutershellexplorer.reg ======

You can find a copy of this file at

http://www.pivx.com/research/freefixes/neutershellexplorer.reg

By combining the above two configuration changes you are protected against exploitation of the Shell protocol, any DHTML Behaviors that use Shell.Explorer for local file referencing, the Akak trojan and any variants thereof. You can verify this independently by testing the MikX PoC [2] or the http-equiv PoC [5]. Remember to close any already open IE windows after you have implemented these changes.

Qwik-Fix Pro users were protected in advance against the Akak trojan without additional updates. You can find a free copy of Qwik-Fix Pro for personal use at

http://www.pivx.com/qwikfixDownload.asp

References:

[1] Akak analysis by Joe Stewart of LURHQ http://www.lurhq.com/akak.html

[2] Proof of Concept code from MikX http://www.mikx.de/scrollbar/

[3] Notes on IE6SP1 by Thor Larholm http://www.securityfocus.com/archive/1/291170/2004-03-22/2004-03-28/2

[4] How to Stop an ActiveX Control from Running in Internet Explorer http://support.microsoft.com/?kbid=240797

[5] Proof of Concept code from http-equiv http://www.malware.com/wottapoop.html

Regards

Thor Larholm Senior Security Researcher PivX Solutions 23 Corporate Plaza #280 Newport Beach, CA 92660 http://www.pivx.com thor@pivx.com Stock symbol: (PIVX.OB) Phone: +1 (949) 231-8496 PGP: 0x4207AEE9 B5AB D1A4 D4FD 5731 89D6 20CD 5BDB 3D99 4207 AEE9

PivX defines a new genre in Desktop Security: Proactive Threat Mitigation. <http://www.pivx.com/qwikfix>