Microsoft said Thursday it plans eventually to patch a vulnerability in Internet Explorer 8 that it's known about for seven months, but it didn't say when.
A security research group within Hewlett-Packard called the Zero Day Initiative (ZDI) released details of the flaw on Wednesday after giving Microsoft months to address it. The group withholds details of vulnerabilities to prevent tipping off hackers but eventually publicizes its findings even if a flaw isn't fixed.
Microsoft said it had not detected attacks that used the vulnerability, which is a "use-after-free" flaw, which involves the handling of CMarkup objects.
The company did not give a reason for the long delay but said in a statement that some patches take longer to engineer and that "we must test every one against a huge number of programs, applications and different configurations."
"We continue working to address this issue and will release a security update when ready in order to help protect customers," it said.
To exploit the flaw, an attacker would have to convince a user to visit a malicious website. If the attack were successful, a hacker would have the same rights as the victim on the computer and could run arbitrary code.
Microsoft's next patch release, known as "Patch Tuesday," is scheduled for June 10. It occasionally issues an emergency patch if a vulnerability is being widely used in attacks.
Wolfgang Kandek, CTO of Qualys, wrote that exploit developers are probably studying ZDI's advisory to try to develop an attack.
"We do not know how quickly an exploit will be released, but the remaining time to Patch Tuesday is not that long," he wrote.
The Belgian researcher who found the flaw, Peter Van Eeckhoutte, wrote on his blog on Thursday that although Microsoft has known of the bug for a long time, "I don't believe this is an indication that Microsoft is ignoring bug reports or doesn't care about security at all, so let's not exaggerate things."
"In fact, Microsoft is doing an excellent job in handling vulnerability reports, issuing patches and crediting researchers," he wrote. "But I would be really worried if the bug was actively being exploited and left unpatched for another 180 days."
In its advisory, ZDI recommended that users set the Internet security zone settings in IE 8 to "high," which blocks ActiveX controls and Active Scripting. Also, using Microsoft's Enhanced Mitigation Experience Toolkit (EMET) would provide more defense, it wrote.
Sign up for CIO Asia eNewsletters.