Breaking news from Trend Micro:
A new zero-day vulnerability in certain versions of Internet Explorer has been identified and is being used in targeted attacks. Microsoft has not released an official bulletin acknowledging this vulnerability yet, but has confirmed that both Internet Explorer 9 and 10 are affected. The newest version, Internet Explorer 11, does not suffer from this vulnerability.
If exploited, this vulnerability allows an attacker to target users with a drive-by download, allowing files to be downloaded and run user systems without any user input needed, beyond visiting a website.
Two versions of Windows are not affected by this threat: Windows 8.1 (because it includes IE11), and Windows XP (because it only supports up to IE8.) All other versions of Windows are at potential risk, depending on the version of Internet Explorer present on the system.
This attack was initially spotted on the website of a non-profit organisation in the United States. The files used in this exploit are detected as HTML_EXPLOIT.PB, HTML_IFRAME.PB, and SWF_EXPLOIT.PB. The backdoor that was planted on affected machines using this zero-day is detected as BKDR_ZXSHELL.V. No formal bulletin or workarounds have been issued by Microsoft; we recommend that users of Windows 7 or 8 consider upgrading to Internet Explorer 11 to avoid this problem.
We are currently analysing both the exploit itself and the payloads used in this attack, and will provide further information as appropriate.