Microsoft has a patch available for a security hole in Internet
Explorer versions 5.5 and 6 that can expose cookie data to
malicious hackers.
The vulnerability was first publicised by Online Solutions, a
Finnish security firm that alerted Microsoft to the hole on 1
November but released the existence and details of the exploit
before Microsoft issued a patch.
Microsoft posted an advisory and recommended that users disable
Active Scripts in IE to prevent their cookie data from being
stolen. However, disabling active scripts also renders some Web
sites unusable.
The vulnerability allows a malicious hacker to write an
intentionally malformed URL in a Web page address. The action
enables a hacker to see the cookies deposited by other Web sites on
the user's hard drive. While proper security practice would not
allow sensitive information to be stored in those cookies, some Web
sites do place credit card and other personal information in
cookies.
A malformed Web address link in an HTML e-mail would also expose
cookie data.
The patch shuts the ability of one Web site to grab information
left by another Web site. The patch also addresses three previously
undisclosed problems, according to the revised bulletin.
"The first two involve how IE handles cookies across domains," the
bulletin states. "Although the underlying flaws are completely
unrelated, the scope is exactly the same - in each case, a
malicious user could potentially craft a URL that would allow them
to gain unauthorised access to a user's cookies and potentially
modify the values contained in them."