It's not Patch Tuesday, but Microsoft has released a crucial update for Internet Explorer that you should apply immediately.
Microsoft included a cumulative update for Internet Explorer in the 13 security bulletins that made up Patch Tuesday last week, and that update was considered Critical as well. Since then, though, a new flaw has been targeted by attacks in the wild, so Microsoft has responded with an out-of-band update.
The update from Microsoft is a Fix-It tool, which is more of a stop-gap bandage than an actual patch. Applying the Fix-It will protect Internet Explorer and prevent the currently circulating exploit from working on your systems.
Paul Henry, security and forensic analyst with Lumension, says that there are number of mitigating factors that limit the potential scope of this threat, but those factors may offer little consolation for many users. "The bad news is that this is a very wide-reaching patch, affecting all versions of IE across all operating systems, from XP to RT," he says. "And more bad news: the average user is very susceptible to being hit with this."
Microsoft claims that running Internet Explorer in Enhanced Security Configuration mode prevents this attack. Internet Explorer runs in this restricted mode by default on Windows Server 2008, Windows Server 2008 R2, Windows Server 2012, and Windows Server 2012 R2.
Microsoft states that all supported versions of Outlook, Outlook Express, and Windows Mail include protection by default as well. HTML email messages are opened by default in the Restricted Sites security zone, which disables scripts and ActiveX controls necessary for the exploit to execute.
However, Microsoft cautions that the protection in Outlook only applies to the HTML message within Outlook itself. If a user receives an email with a link and clicks on it, they're still potentially vulnerable because the threat is now Web-based and functioning outside of Outlook.
"The average user does not run the restricted sites mode, are not using the Enhanced Security Configuration and are all-too-willing to click on phishing emails," Henry explains, "I recommend employing the mitigating factors, as well as advising users about this so they will be less likely to click malicious links until you can apply the patch. It's been a while since we've seen an out-of-band patch for IE from Microsoft, but it's still important to apply it as soon as possible."
"It's important to reiterate that ALL versions of IE are affected including the Internet Explorer 11 preview, Tyler Reguly, technical manager of security research and development for Tripwire, says. "Since attacks are occurring now, this is a situation where it's in everyone's best interest for Microsoft to release a patch as soon as possible. In the meantime, install the shim that they've released."
He adds, "For less technical users that aren't comfortable with Microsoft Fix it solutions, using another browser until a patch is available is the best option,"
A couple additional notes: The Fix-It solution only works with 32-bit versions of Internet Explorer, and you must first apply the cumulative update for Internet Explorer from last week's Patch Tuesday (MS13-069).