The Cligs URL shortening site was hacked during the weekend to cause 2.2 million links to redirect to the same site.
When users clicked on a link that had been reduced in character count by Cligs, instead of going to the expected site, they went to a page on the Orange County Register newspaper website. The site wasn't malicious, nor had it been compromised.
“Normally most hacking attacks we see today are all about money,” Graham Cluley, senior technology consultant at Sophos, told SCMagazineUS.com on Tuesday. “Normally, you'd see a redirect to a site that installs malware or some other money-maker. But there is no evidence of that at all.”
The motive for the redirect hack remains unclear. It could have been an attempt at a distributed denial-of-service (DDoS) attack, but little evidence exists that it was effective.
“It could have been a mistake,” Cluley said. “They could have wanted to redirect people to one place, but misspelled something and sent everyone to the wrong place.”
The method by which the hack was made is unknown as well, and Cligs has not gone into detail other than to say that there was a security hole in its functionality that enabled users to edit an old link. If a link was set up on the site and later discovered to contain a mistake, it may have been possible to go back and change it.
“The security hole may have enabled hackers to edit links that were not theirs,” Cluley explained.
What should users do to guard against possible malicious redirects? Because, by their very nature, URL shorteners obscure the real URL, Cluley suggested that it would be prudent to have a browser plug-in, script or other functionality that always expands URLs automatically.
“With that functionality, it means you will at least know where you are going before you go there,” he said.
The lesson here is how a single vulnerability could potentially cause widespread damage on the internet.
“This is a single point of weakness where hackers were able to break in and potentially affect a large number of people,” Cluley said. “Normally, it would be a lot more complicated to influence so many links."
Cligs is the fourth most popular URL-shortening service on Twitter.