A flaw in the way Microsoft's Internet Explorer browser processes FTP commands
could let attackers steal or erase data from a victim's FTP site.

The bug, which affects users of IE 6 and the unsupported IE 5 browser, gives
an attacker a way of hijacking the victim's FTP sessions. But a successful attack
would be very hard to pull off and would only work in very precise, targeted
attacks, security experts said.

The attacker would need to know the victim's username on the FTP server and
the victim would have to already be logged into the server, using IE. Under
those conditions, the victim could be sent a malicious FTP link that would then
execute commands on the victim's FTP server.

This link could be sent to the browser via an invisible iFrame component, hidden
on a malicious Web site, so the victim might not even know the attack was taking
place.

"It's something that people could use to steal data, but you'd have to
know your target," said Derek Abdine, the principal software engineer with
security vendor Rapid7, who disclosed the issue Monday in a security
advisory.

"The attack seems viable, but the stars have to be aligned just right
for the attack to work," said Craig Schmugar, a researcher with McAfee's
Avert Labs, in an e-mail. "An administrator would need to be authenticated
already or the server would need to be configured with weak credentials."

Rapid7 notified Microsoft of the issue on Jan. 22 and decided to publish proof-of-concept
code that illustrated the flaw after Microsoft had not patched the issue a month
later.

The flaw is "almost exactly the same" as another
IE FTP flaw that Microsoft patched in August 2006, Abdine said. Microsoft
fixed that bug with its MS06-042 patch, issued in August 2006.

The MS06-042
update fixed many IE vulnerabilities, but it ended up embarrassing Microsoft.
That's because the security patch had a flaw of its own, a critical security
vulnerability that sent Microsoft's security team scrambling to re-issue the
update.

The FTP problem does not affect IE 7, Microsoft said Tuesday. The software
vendor has not heard of any attacks that take advantage of this vulnerability
and has determined that any successful attack would only lead to the unauthorized
disclosure of data, the company said in a statement.

IDG News Service

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