Microsoft has issued a cumulative patch for Internet Explorer, which fixes multiple vulnerabilities. The worst vulnerability can lead to execution of arbitrary code on the client system via HTML emails or web sites.

1) A cross domain vulnerability exists in the way Internet Explorer retrieves files from the cache. This can be exploited by a malicious HTML document to execute arbitrary scripting in the "My Computer Zone".

2) Internet Explorer determines whether an object is safe when it interprets the file extension specified in the "Object Data" tag. This allows a malicious person to specify a "safe" file with eg. a ".html" extension in "Object Data", which causes Internet Explorer to interpret it as a "safe" file. However, when the file is retrieved by Internet Explorer the "Content-Type" header determines how the file will be treated. This allows an executable file like a ".hta" file to be treated as a "safe" file and be executed silently without restrictions.

NOTE: Further information has been released by http-equiv, proving that the patch from Microsoft is not adequate. Refer to solution section.

Secunia has constructed a vulnerability test, which can be used to check if you are affected by this issue:
http://secunia.com/MS03-032/


3) The Kill Bit will be set on the Windows Reporting Tool ActiveX control "BR549.DLL". This ActiveX control contains a vulnerability which could be exploited by malicious HTML documents to execute arbitrary code.

Furthermore, a language specific variant of the older object type tag buffer overflow vulnerability (MS03-020) has been identified and is fixed in this patch.

This update also fixes other minor issues.

The "Object Data" vulnerability is straight forward to exploit. In many ways this vulnerability is similar to MS01-020 which was exploited by notorious viruses like Nimda, Badtrans and Klez.


NOTE: Secunia has discovered exploitation of the "Object Data" vulnerability in the wild. Analysis shows that the exploit installs a program called ADPlus module or SurferBar, which is added to a users Internet Explorer and contains links to various porn sites. The exploit does the following:

1) User receives an email, which exploits the "Object Data" vulnerability.
2) The resource "a.cgi" is automatically requested from a webserver (63.246.130.201), which installs the file "drg.exe" in "C:\".
3) The file is then executed and saves the resource "surferbar.dll" from the same webserver as "win32.dll" (originally named "adplus.dll") in the "C:\\Program Files\" directory.
4) The file "win32.dll" is then executed by "regsvr32" and adds a bar to the user's Internet Explorer.

Solution
This has been superceded by MS03-040:
Further details available to Secunia VIM customers

Provided and/or discovered by
1) Yu-Arai, LAC
2) Drew Copley, eEye Digital Security
3) Greg Jones, KPMG UK

http-equiv has supplied additional information about exploitation of the "Object Data" vulnerability.

Changelog
Further details available to Secunia VIM customers

Original Advisory
http://www.microsoft.com/technet/security/bulletin/MS03-032.asp
http://www.eeye.com/html/Research/Advisories/AD20030820.html

Other references
Further details available to Secunia VIM customers

Deep Links
Links available to Secunia VIM customers