Microsoft today announced it will issue an emergency security update for Internet Explorer (IE) tomorrow to patch a zero-day vulnerability that has been used to launch drive-by attacks for at least several weeks.
Tuesday's update will be the second out-of-band update -- Microsoft's term for one outside its normal once-each-month Patch Tuesday -- in the last three months. Microsoft last shipped a rush IE update to customers in late January, to fix eight flaws, including one that had been used to attack several companies' networks, including Google's and Adobe's.
"The bulletin is being released to address attacks against customers of Internet Explorer 6 and Internet Explorer 7," said Microsoft in an updated advisory.
As it did in January, Tuesday's out-of-band update will patch more than just the zero-day. It will, in fact, plug critical holes in every edition of IE, including the newest, IE8. "The out-of-band security bulletin is a cumulative security update for Internet Explorer and will also contain fixes for privately reported vulnerabilities rated Critical on all versions of Internet Explorer that are not related to this attack," said Microsoft today.
Microsoft first warned users of the vulnerability in IE6 and IE7 on March 9, saying at the time that the bug didn't affect the browser's oldest and newest editions, IE 5.01 and IE8, respectively. At the time, Microsoft called the attacks "targeted," a term it uses to describe small-scale exploitations.
Today's announcement caught researchers by surprise. "I thought it would take longer than this," said Wolfgang Kandek, the chief technology officer of security vendor Qualys. "The fact that it's coming out now tells me that Microsoft is seeing a real reason to patch before the next [Patch Tuesday]. They accelerated this update for a reason, so I think that they've seen the attacks increasing."
Andrew Storms, director of security operations at nCircle Network Security, agreed. "I wasn't necessarily expecting it. It's been less than a month since Microsoft issued its advisory," he said. "But they wouldn't move the timeline unless there was a good reason."
Like Kandek, Storms assumed that Microsoft pushed up the release of its cumulative IE update because it has seen an increase in attacks exploiting the zero-day.
Microsoft may patch two other outstanding vulnerabilities in IE, Storms added, ticking off a pair of security advisories the company has issued this year. In February, Microsoft warned of a bug in IE running on Windows XP that could be used by hackers to access files on the PC; earlier this month, Microsoft told Windows XP users not to press the F1 key when prompted by a Web site, citing an unpatched vulnerability that attackers could exploit to hijack PCs running the browser.
Tomorrow's update for IE will apply to all versions of the browser -- IE 5.01, IE6, IE7 and IE8 -- and affect all supported editions of Windows, including Windows 2000, XP, Vista, Server 2003, Server 2008, Windows 7 and Server 2008 R2.
If it follows its usual timetable, Microsoft will issue the update sometime after 1 p.m. ET.
Gregg Keizer covers Microsoft, security issues, Apple, Web browsers and general technology breaking news for Computerworld. Follow Gregg on Twitter at @gkeizer or subscribe to Gregg's RSS feed . His e-mail address is email@example.com.