Index Server is installed by default in all IIS (Internet Information Server) systems and is included natively in Windows 2000 and XP. The flaw comes into play in an ISAPI (Internet Services Application Programming Interface) extension associated with the Index Server, according to the company. If a certain kind of attack is mounted on a server running the software, the memory buffer can be overrun, giving the attacker control of the server, Microsoft said.
If Index Sever has been installed on its own, without IIS, there is no vulnerability, according to Scott Culp, security program manager at the Microsoft security response centre. However, the flaw is exploitable when the Index Server is present in conjunction with IIS -- which is the way most users will have it configured, Culp said. Even if the Index Server is disabled and IIS is running, the flaw is present, he said.
Microsoft issued a patch to fix the flaw at the same time it released the security bulletin containing the information. If users have been uninstalling unneeded software, as Microsoft recommends, those customers should not be vulnerable, Culp said. Users are presented with a checklist and an automated way to search for and uninstall unneeded components, he said.
Microsoft has spread word of the flaw to subscribers to its security notification service, industry analysts, IT security partners and others, Culp said. Additionally, some Microsoft customers are being contacted directly about the bug.
Monday's flaw is not the first to be found in IIS since the beginning of May. At least two such flaws have been found, one serious enough to allow an attacker to gain complete control of the affected systems. The first flaw also involved a problem with an ISAPI extension, this time one enabling Internet printing, and the second could have lead to Denial of Service attacks.
"The effect of successfully exploiting this vulnerability is just as serious" as the first ISAPI bug, Culp said, adding that though both exploited ISAPI extensions, the two flaws were not particularly related.
EEye Digital Security, the security firm who found the first ISAPI bug, also discovered this flaw.