The vulnerabilities were reported in online security forums on Monday, according to a posting on the McAfee Avert Labs blog on Tuesday. All but one of the flaws results in denial of service, meaning the application would crash, according to the blog post.
"There is one heap-overflow flaw that might be exploited for code execution," Karthik Raman, a McAfee researcher wrote on the blog on Tuesday. Typically such flaws are exploited by tricking a targeted victim into opening a rigged Office document.
Microsoft is investigating the bug reports as well, a company representative said in an e-mailed statement. The initial investigation has found that none of these zero-day claims demonstrates any vulnerability in the products of Office 2007, the latest version of Office, the representative said. Also, Microsoft is not aware of any attacks that exploit any of the issues at this time, he said.
In addition to the Office bugs, a zero-day vulnerability has been reported in Windows. Sample code that exploits a flaw in the way Windows handles help system files has been posted to the Internet.
"This is another heap-overflow flaw that might be exploited for code execution," McAfee's Raman wrote in an update to the Avert Labs blog late Tuesday.
Microsoft said it is aware of the issue. "Microsoft has listed .hlp files as unsafe file types and recommends customers exercise the same cautions with .hlp as .exe, as both file types are executable," it said. An attacker would have to use rigged .hlp files to exploit the flaw, according to Microsoft.
Word of the flaws comes on the day that Microsoft issued five security bulletins as part of its monthly patch cycle. The company is still dealing with the aftermath of an emergency patch released last week.
"This is yet another time that zero-day flaws have been published around a Patch Tuesday, possibly to maximize the exposure to these flaws until the next month�s Patch Tuesday," Raman wrote.
Cybercrooks have found that they can take advantage of Microsoft's security update cycle by timing new attacks right before or just after Patch Tuesday--the second Tuesday of each month when the software maker releases its fixes. Some security watchers have coined the term "zero-day Wednesday" to describe that strategy.
McAfee is still investigating the security vulnerabilities. They may not actually all be new, said Dave Marcus, security research and communications manager at the Santa Clara, Calif.-based security firm. "Sometimes what people claim to be zero-days may in fact be related to something that's already known," he said.
Should the three Office bugs be new, the tally of zero-day vulnerabilities in the productivity suite waiting for a fix would jump to five. Microsoft did not deliver any patches for Office on Tuesday, despite two vulnerabilities in the software that have been previously disclosed, according to eEye Security's zero-day flaw tracker.