China has been actively diverting unencrypted Web traffic destined for its top online search service — Baidu.com — so that some visitors from outside of the country were unwittingly enlisted in a novel and unsettling series of denial-of-service attacks aimed at sidelining sites that distribute anti-censorship tools, according to research released this week.
The findings, published in a joint paper today by researchers with University of Toronto’s Citizen LabCitizen Lab, the International Computer Science Institute (ICSI) and the University of California, Berkeley, track a remarkable development in China’s increasingly public display of its evolving cyber warfare prowess.
“Their willingness to be so public mystifies me,” said Nicholas Weaver, a researcher at the ICSI who helped dig through the clues about the mysterious attack. “But it does appear to be a very public statement about their capabilities.”
Earlier this month, Github — an open-source code repository — and greatfire.org, which distributes software to help Chinese citizens evade censorship restrictions enacted by the so-called “Great Firewall of China,” found themselves on the receiving end of a massive and constantly-changing attack apparently designed to prevent people from being able to access the sites.
Experts have long known that China’s Great Firewall is capable of blocking Web surfers from within the country from accessing online sites that host content which is deemed prohibited by the Chinese government. But according to researchers, this latest censorship innovation targeted Web surfers from outside the country who were requesting various pages associated with Baidu, such that Internet traffic from a small percentage of surfers outside the country was quietly redirected toward Github and greatfire.org.
This attack method, which the researchers have dubbed the “Great Cannon,” works by intercepting non-Chinese traffic to Baidu Web properties, Weaver explained.
“It only intercepts traffic to a certain set of Internet addresses, and then only looks for specific script requests. About 98 percent of the time it sends the Web request straight on to Baidu, but about two percent of the time it says, ‘Okay, I’m going to drop the request going to Baidu,’ and instead it directly provides the malicious reply, replying with a bit of Javascript which causes the user’s browser to participate in a DOS attack, Weaver said.
The researchers said they tracked the attack for several days after Github apparently figured out how to filter the malicious traffic, which relied on malicious Javascript files that were served to visitors outside of China that were browsing various Baidu properties.
Chillingly, the report concludes that Chinese censors could just have easily served malicious code to exploit known Web browser vulnerabilities.
“With a minor tweak in the code, they could have provided exploits to targeted [Internet addresses], so that instead of intercepting all traffic to Baidu, they would serve malware attacks to those visitors,” Weaver said.
