WordPress pingback feature exploited for attack amplification to knock a WordPress site offline
Online criminals have leveraged a feature used by more than 162,000 WordPress sites to launch a large distributed denial of service (DDoS) attack.
They took advantage of Pingback, which seeks a file known as XML-RPC, a remote procedure call protocol that uses XML to encode its calls and HTTP to take it over the Internet. As that responds with a decent level of traffic, it makes for a handy amplifier.
DDoS over WordPress
Security firm Sucuri, which detected the attack, did not fully explain how the anonymous target was knocked offline. It’s likely this was a typical amplification DDoS, where the attacker spoofed the IP address of the target, sent out Pingbacks to the thousands of WordPress sites that had the feature switched on, which subsequently sent large volumes of traffic to the victim, which was also a WordPress site.
“Just in the course of a few hours, over 162,000 different and legitimate WordPress sites tried to attack his site. 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,” Sucuri said in a blog post.
“Can you see how powerful it can be? One attacker can use thousands of popular and clean WordPress sites to perform their DDoS attack, while being hidden in the shadows, and that all happens with a simple ping back request to the XML-RPC file.
“This is a well known issue within WordPress and the core team is aware of it, it’s not something that will be patched though. In many cases this same issue is categorized as a feature, one that many plugins use, so in there lies the dilemma.”
WordPress users who don’t want to be part of these attacks can either add a plugin that includes a preventative filter, or disable the feature altogether.
Attackers are leveraging a wide range of amplifiers, including age-old protocols like the Network Timing Protocol, which can produce epic traffic from small requests.
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