There is a new and unpatched vulnerability with exploit code in the wild that affects the latest version of IE. The exploit works by including an abnormally large (a couple thousand) number of script actions inside a single HTML tag.
This vulnerability can be triggered by specifying more than a couple
thousand script action handlers (such as onLoad, onMouseMove, etc) for any
single HTML tag. Due to a programming error, MSIE will then attempt to
write memory array out of bounds, at an offset corresponding to the ID of
the script action handler multiplied by 4 (due to 32-bit address clipping,
the result is a small positive integer).The list of IDs can be found on the Web, and is as follows (values in
parentheses = resulting offsets):onhelp = 0x8001177d (+0x45df4)
onclick = 0x80011778 (+0x45de0)
ondblclick = 0x80011779 (+0x45de4)
onkeyup = 0x80011776 (+0x45dd8)
onkeydown = 0x80011775 (+0x45dd4)
onkeypress = 0x80011777 (+0x45ddc)
onmouseup = 0x80011773 (+0x45dcc)
onmousedown = 0x80011772 (+0x45dc8)
onmousemove = 0x80011774 (+0x45dd0)
onmouseout = 0x80011771 (+0x45dc4)
onmouseover = 0x80011770 (+0x45dc0)
onreadystatechange = 0x80011789 (+0x45e24)
onafterupdate = 0x80011786 (+0x45e18)
onrowexit = 0x80011782 (+0x45e08)
onrowenter = 0x80011783 (+0x45e0c)
ondragstart = 0x80011793 (+0x45e4c)
onselectstart = 0x80011795 (+0x45e54)
This will cause a memory array to write out of bounds and cause overflow in Microsoft Internet Explorer (mshtml.dll) and as result an immediate or eventual browser crash. Both McAfee and Symantec have released signatures to detect this exploit. While this is only a DoS vulnerability at the moment, there is ongoing attempts to try to use this as a vector for remote code execution.
Tested on MSIE 6.0.2900.2180.xpsp2.040806-1825 on Windows XP SP2. As far
as I can tell, other browser makes (Firefox, Opera) are not susceptible to
this attack.
Thanks to SecurityFocus
