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Conficker call-backs threaten to swamp legit domains

Southwest Airlines faces Friday the 13th horror

Seven Steps to Software Security

The infamous Conficker worm is set to disrupt the operation of at least four legitimate websites this month.

Machines infected with Conficker (Downadup) are programmed to dial home for updates through a list of domains which changes every day. Microsoft is heading an alliance to block unregistered domains on this list but that still leaves a number of registered domains on the storm front.

An analysis by Sophos identified that of 7750 Conficker call-home domains found around half are active (ie resolve to an IP address). Fortunately the vast majority of these (3,861 from 3,889) domains resolve to only 42 unique IP addresses. That leaves 28 domains to worry about, most of which are up for sale with registrars.

That still leaves four frequently-visited legitimate domains which will, for one day at least, be left on the speed-dial list of infected machines. Jogli.com (Big Web Great Music) is due for a call up on 8 March, followed by wnsux.com (which is run as a secondary domain by Southwest Airlines) on the 13 March, qhflh.com (Women's Net in Qinghai Province, China) five days later and praat.org on the 31 March.

Instead of facing a near-invulnerable homicidal nutter in a hockey mask, Southwest Airlines website faces a zombie onslaught this Friday the 13th.

"A legitimate domain that happens to make it into the Conficker call-home list is a problem for two reasons," explained Mike Wood of SophosLabs, Canada. "First, without proper investigation, they may end up on a blocklist and prevent users from accessing their services.

"Second, those millions of Conficker infected machines contacting the domain on its given day may overload the site and essentially result in a denial-of-service attack."

The websites affected stand to be swamped with requests for updates from infected machines on the relevant days. In the worse case scenario, that means online check-ins with Southwest Airlines on Friday, 13 March might become impossible.

Sophos suggests either suspending the affected domains, and using an alternative domain, or filtering the HTTP query that Conficker uses, as techniques to avoid a possible denial of service attack. Filtering HTTP requests is a heavy lifting job, and technically tricky. Sophos has contacted the sites on the hitlist who face real problems, with the sole upside being that they have some notice of the imminent blow. ®

Mobile application security vulnerability report

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