Just as Microsoft omitted a patch for a two-month-old flaw in Word 2000 and 2002 from its monthly updates Tuesday, three more bugs in the company's Office suite were disclosed by a security researcher.
Microsoft confirmed it is investigating but downplayed any threat.
Mati Aharoni, of Offensive Security, used a pair of security mailing lists to warn of three new unpatched flaws in Word 2007; McAfee's blog picked up on the Milw0rm and SecurityVulns.com postings Tuesday. Aharoni also posted malformed Word documents as proof-of-concepts for the trio.
Aharoni said he found the flaws using a "fuzzer," a tool that probes an application for vulnerabilities by sending random input. Two of the three bugs result in a denial-of-service-like situation, with the PC's processor maxed out at 100 percent, making the machine unusable until it's rebooted. The third, Aharoni suggested, could be used to introduce remote attack code after an exploit causes an overflow of "wwlib.dll," a crucial Word library. But "code execution is not trivial," he added.
"Microsoft is investigating new public reports of possible vulnerabilities in Office," a company spokeswoman said Wednesday in an e-mail. "Microsoft is not aware of any attacks attempting to use the reported vulnerability or of customer impact at this time."
She also downplayed the threat. "Microsoft's initial investigation has found that none of these claims demonstrate any vulnerability in Word 2007 or any Office 2007 products."
Microsoft, however, typically separates bugs that allow code execution or rights elevation from those that result in denial of service -- in other words, a vulnerability that ends up crashing the affected application or the computer. It is not denying the possible existence of the Aharoni-disclosed bugs, however.
"Upon completion of this investigation, Microsoft will take the appropriate action to protect our customers, which may include issuing a security advisory or providing a security update through our monthly release process," the spokeswoman concluded.
Word users are already waiting for a fix for a vulnerability acknowledged by Microsoft in mid-February. That bug, which affects both Word 2000 and Word 2002, has been exploited by attackers for at least two months. However, Microsoft skipped its March security updates and didn't include a fix in the bulletins issued Tuesday.
The timing of the new Office 2007 vulnerability disclosures was probably not coincidental; researchers have taken to publicizing bugs and/or posting exploit code immediately after Microsoft releases its monthly batch of patches.
"This is yet another time that zero-day flaws have been published around a Patch Tuesday," noted Karthik Raman, the McAfee analyst who blogged on the bugs. "[That's] possibly to maximize the public's exposure to these flaws until the next month's Patch Tuesday."