The vulnerability in the browser's Active Setup Download feature could enable malicious hackers or website operators to launch denial-of-service attacks, Microsoft said in a bulletin that accompanies the patch. The fix for the security hole was released last Thursday.
The Active Setup control detects which files are needed by users who are updating software and then downloads the relevant ones. It's supposed to check to see whether the files are digitally signed before downloading them and warn users if files aren't signed or are signed by someone who doesn't have proper authorisation, according to Microsoft.
But the mechanism has two flaws, Microsoft said. First, Microsoft-signed files are treated as trusted content, which means Internet Explorer will download them without asking for a user's approval. In addition, the control allows download locations to be specified on a user's hard drive, which Microsoft said could give malicious attackers a tool for overwriting system files and rendering machines unusable.
However, Microsoft added that attackers couldn't modify files or cause other damage to a computer other than crashing the system. The flaw affects Versions 4, 4.01, 5 and 5.01 of Internet Explorer, the company said.