Researchers at Sucuri have discovered an attack abusing a commonly-used feature of WordPress to launch a distributed denial-of-service (DDoS) attack.
According to Sucuri, the attack took advantage of WordPress' Pingback function, which essentially notifies the author of a blog that another blog has linked to his or her blog post. In a blog post, Sucuri CTO Daniel Cid explained that any site that has Pingback enabled - which it is by default - can be used in DDoS attacks against other sites.
"It all happened against a popular WordPress site that had gone down for many hours due to a DDOS," blogged Cid. "As the attack increased in size, their host shut them down, and then they decided to ask for help and subscribed to our CloudProxy Website Firewall."
"Once the DNS was ported we were able to see what was going on, it was a large HTTP-based (layer 7) distributed flood attack, sending hundreds of requests per second to their server," he noted, adding that all queries had a random value that bypassed their cache and forced a full page reload every single time.
The most interesting part however is that all the requests were coming from legitimate WordPress sites.
"Just in the course of a few hours, over 162,000 different and legitimate WordPress sites tried to attack his site," Cid wrote. "We would likely have detected a lot more sites, but we decided we had seen enough and blocked the requests at the edge firewall, mostly to avoid filling the logs with junk."
According to Cid, users can stop theier WordPress sites from being misused by disabling the XML-RPC functionality on their site.
Last year, researchers at Incapsula reported an attack using the same method.