Last month's hack of RSA Security began with an exploit of a then-unpatched vulnerability in Adobe Flash Player, the company confirmed Friday.
According to RSA, attackers gained access to its network by sending two small groups of employees e-mails with attached Excel spreadsheets. One of those employees opened the attachment, which was titled "2011 Recruitment plan.xls."
The spreadsheet contained an embedded Flash file that exploited a "zero-day" vulnerability -- a bug then unknown to Adobe, and thus unpatched -- that allowed hackers to commandeer the employee's PC.
From there, the attackers installed a customized variant of the Poison Ivy remote administration tool (RAT) on the compromised computer. Using the RAT, hackers harvested users' credentials to access other machines within the RSA network, searched for and copied sensitive information, and then transferred the data to external servers they controlled.
Although RSA has not detailed what was stolen, it has admitted that information related to the company's SecurID two-factor authentication products was part of the hacker's haul.
Last week's description of the Flash attack vector helps explain the reaction of Adobe and others to the flaw, and shows that RSA was hacked at least several days before the company went public.
RSA first reported the attack and the data theft late on Thursday, March 17.
Three days before that, however, Adobe had issued a security advisory acknowledging that attackers were exploiting an unpatched bug in Flash Player using tricked-out Excel documents.
"There are reports that this vulnerability is being exploited in the wild in targeted attacks via a Flash (.swf) file embedded in a Microsoft Excel (.xls) file delivered as an e-mail attachment," Adobe said in the March 14 advisory.
At the time, Adobe did not name RSA as the target of the ongoing attacks.
But Adobe did promise to patch the Flash vulnerability the next week, a promise it kept when it shipped an "out-of-cycle" update of the popular media player seven days later, on Monday, March 21.
Adobe has delivered emergency patches for Flash before. In 2010, for instance, it rushed out fixes three times, one in only six days, the other two times in seven days each.
In hindsight, the seriousness of the Flash vulnerability should have been apparent. On March 17, Microsoft told Office users to protect themselves by running an advanced configuration tool.
Microsoft made those recommendations several hours before RSA's top executive admitted that his company's network had been breached.
The RSA employee who opened the attack Excel file must have been using a version of Office earlier than Office 2010. In a March 17 blog post, a manager and security engineer with the Microsoft Security Response Center (MSRC) said that Excel 2010 was not susceptible to the attacks then circulating.
Excel 2010 automatically enables DEP (data execution prevention), a key Windows anti-exploit technology, and also isolates malicious files inside Office 2010's "Protected View," a "sandbox" that prevents attack code from escaping the application.
Older versions of Excel, including those in Office 2003 and Office 2007, were not protected by DEP or Protected View, said Microsoft.
While RSA has characterized the attack as an "advanced persistent threat," or APT -- an oft-used label for slow, stealthy attacks, typically attributed to Chinese hackers -- some security experts seemed to see it as just ordinary.
"2 emails and a Adobe Flash 0-day and you too can be an APT!" said Jeremiah Grossman, the CTO an WhiteHat Security, on Twitter Friday.