Microsoft confirms zero-day flaw in IIS

Microsoft is not currently aware of active attacks on the IIS flaw

Microsoft has warned of a new zero-day vulnerability in its Internet Information Services (IIS) which could allow remote code execution by hackers.

The company has issued a security advisory for the vulnerability, which lies in the File Transfer Protocol (FTP) service in IIS 5.0, 5.1 and 6.0.

Microsoft said that, although the code has been published widely on the internet, the firm is "not currently aware of active attacks that use this exploit code, or of customer impact at this time".

"The vulnerability is a stack overflow in the FTP service when listing a long, specially-crafted directory name," the company said in a Security Research and Defense blog post.

"To be vulnerable, an FTP server would need to grant untrusted users access to log into and create that long, specially-drafted directory. If an attacker were able to successfully exploit this vulnerability, they could execute code in the context of LocalSystem, the service under which the FTP service runs."

Microsoft is advising companies to prevent untrusted users from having write access to the FTP service until a fully-tested security update is available. This can be achieved by turning off the FTP service if it is not needed, or preventing anonymous users from writing via IIS settings, said the blog posting.

IIS is the second most popular web server in the world after Apache, according to the latest figures.