For the second time this month, Adobe has issued an emergency software update to fix a critical security flaw in its Flash Player software that attackers are already exploiting. Separately, Microsoft released a stopgap fix to address a critical bug in Internet Explorer versions 9 and 10 that is actively being exploited in the wild.

The vulnerabilities in both Flash and IE are critical, meaning users could get hacked just by visiting a compromised or booby-trapped Web site. The Flash patch comes just a little over two weeks after Adobe released a rush fix for another zero-day attack against Flash.

Adobe said in an advisory today that it is aware of an exploit that exists for one of three security holes that the company is plugging with this new release, which brings Flash Player to v. 12.0.0.70 for Linux, Mac and Windows systems.

This link will tell you which version of Flash your browser has installed. IE10/IE11 and Chrome should auto-update their versions of Flash, although IE users may need to check with the Windows Update feature built into the operating system.

If your version of Flash on Chrome (on either Windows, Mac or Linux) is not yet updated, you may just need to close and restart the browser. The version of Chrome that includes this fix is v. 33.0.1750.117 for Windows, Mac, and Linux. To learn what version of Chrome you have, click the stacked bars to the right at of the address bar, and select “About Google Chrome” from the drop down menu (the option to apply any pending updates should appear here as well).

The most recent versions of Flash are available from the Adobe download center, but beware potentially unwanted add-ons, like McAfee Security Scan). To avoid this, uncheck the pre-checked box before downloading, or grab your OS-specific Flash download from here. Windows users who browse the Web with anything other than Internet Explorer will need to apply this patch twice, once with IE and again using the alternative browser (Firefox, Opera, e.g.).

As I noted in my Tools for a Safer PC primer, blocking Javascript by default in your Web browser is the best way to block browser-based attacks — including these Flash zero-day flaws. Several Mac users have written in recently to ask about the whereabouts of a Tools for a Safer Mac post, and while that’s a good idea (and a post that may soon be coming), script-blocking via extensions/add-ons like NoScript and NotScripts is an approach that works across multiple OSes.

Another great cross-platform approach to blocking Flash (and Java) content by default is Click-to-Play, a feature built into Google Chrome, Mozilla Firefox and Opera (and available via add-ons in Safari) that blocks plugin activity by default, replacing the plugin content on the page with a blank box. Users who wish to view the blocked content need only click the boxes to enable the Flash or Java content inside of them. Check out this post for more details on deploying Click-to-Play.

MICROSOFT FIX-IT TOOL

Microsoft has released a security advisory and a FixIt shim tool for a previously unknown zero-day vulnerability in Internet Explorer versions 9 and 10. Microsoft says it is aware of “limited, targeted attacks” that attempt to exploit a vulnerability in Internet Explorer 10. Only Internet Explorer 9 and Internet Explorer 10 are affected by this vulnerability. Other supported versions of Internet Explorer are not affected.

Microsoft says it is working on an official patch, but that in the meantime IE users should consider taking advantage of a new FixIt solution. According to Microsoft, applying the Microsoft Fix it solution here prevents the exploitation of this issue.

Microsoft warns that IE users should make sure they have the latest version of IE before appyling this FixIt solution (that means a visit to Windows Update). Also, the company says that after you install this Fix it solution, you may experience increased memory usage when you use Internet Explorer to browse the web. This behavior apparently occurs until you restart Internet Explorer.

Tags: 0day, chrome, Flash Player v. 12.0.0.70, Flash Player zero day, IE zero day, Internet Explorer 0day, Mac, Microsoft FixIt, windows