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Why Hotmail could spread viruses even faster than Outlook
From: William Knowles <wk () c4i org>
Date: Sat, 2 Jun 2001 02:18:17 -0500 (CDT)


By John Leyden
Posted: 01/06/2001 at 17:21 GMT

A flaw in the web-based email services run by the likes of Yahoo! and
Hotmail makes them conduits through which mass mailing email viruses
can rapidly spread over the Internet.

That's the serious warning contained in a posting to the BugTraq
security mailing list by a security researcher who said that
cross-site scripting vulnerabilities make it possible to replicate
Melissa-type worms through Web mail services.

To exploit the vulnerability an attacker would send an email to a
victim, within which is a link to a service provider's own server.
This link would contain Javascript that executes when the page is
loaded and opens a window that could navigate through the victim's
inbox, sending messages with the malicious link to every email address
it finds in the inbox.

The trick of this exploit is that since the malicious Javascript
executes inside a page from the mail service's own server, no
domain-bounding error is triggered when the Javascript is controlling
the window with the victim's inbox.

Although the exploit requires a user to click on a link, the fact that
a malicious email comes from a trusted source and contains a link to a
familiar, trusted server works in favour of any worm created which
makes use of the security loophole.

The vulnerability was discovered by a white-hat hacker called Matt
Parcens who has posted an advisory on the issue and the steps that
need to be taken to address the issue here.

Both Yahoo! and Hotmail were notified of the issue on May 23 but it's
not known if a fix has been put in place, or which other services
might be affected.

Jack Clark, European product manager at Network Associates, whose
McAfee division provides the antivirus software used by Hotmail said
that the threat looks "plausible" and that its researchers were
investigating the issue with a view to developing a fix.

He questioned the motives of Parcens in posting details of the
vulnerability so soon after notifying the firms involved which he
compared to trying the locks on various door and then posting details
of whose doors were left open on the Internet.

[Yahoo/Hotmail Advisory:  
http://www.sidesport.com/webworm/cl_advisory.html ]

"Communications without intelligence is noise;  Intelligence
without communications is irrelevant." Gen Alfred. M. Gray, USMC
C4I.org - Computer Security, & Intelligence - http://www.c4i.org

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