Large DDoS attack brings WordPress pingback abuse back into spotlight

Attackers exploited the pingback feature in WordPress to use 160,000 WordPress sites as DDoS proxies, researchers from Sucuri said

Attackers have abused the WordPress pingback feature, which allows sites to cross-reference blog posts, to launch a large-scale, distributed denial-of-service (DDoS) attack, according to researchers from Web security firm Sucuri.

The attack involved over 162,000 legitimate WordPress websites being forced to send hundreds of requests per second to a popular WordPress site, preventing access to it for many hours, said Daniel Cid, the CTO of Sucuri, in a blog post Monday. The affected site wasn't named.

The attack exploited an issue with the XML-RPC (XML remote procedure call) implementation in WordPress that's used for features like pingback, trackback, remote access from mobile devices and others, and brought back into the spotlight the denial-of-service risks associated with this functionality that have been known since 2007.

"Any WordPress site with XML-RPC enabled (which is on by default) can be used in DDoS attacks against other sites," Cid said in the blog post.

The recent incident investigated by Sucuri attackers sent XML-RPC requests to legitimate WordPress sites instructing them to make pingback calls to randomly generated URLs on the targeted site.

Most WordPress sites have caching enabled, which means they serve previously visited pages from their cache. This puts less stress on the server than it would take to generate and serve those pages every time.

However, by using random URLs that don't actually exist, the attackers bypassed the caching mechanism and forced the target site to perform full page reloads.

Unlike network-layer attacks, attacks like this one that target the application layer don't require a lot of bandwidth to be successful, Cid said Tuesday via email.

For attackers, the advantage of abusing the WordPress pingback feature in this manner is that they can spread their attacks over a large number of unique IP addresses, making it harder for the targeted sites to block them, Cid said. "It does not amplify the bandwidth utilization, but the scale and reach of the attack."

The WordPress bug ticket related to the pingback DDoS issue was originally created in 2007 and reveals that WordPress' developers tried to partially mitigate the problem with several patches over the years, last time in WordPress 3.6, which was released in August.

However, completely disabling XML-RPC in the platform itself is unlikely because it's needed for important features.

"I spoke to the WordPress team and they are investigating ways to minimize this issue, while still having the pingback functionality available (which is important for them)," Cid said.

However, Matt Mullenweg, the WordPress project lead, doesn't agree with Sucuri's suggestion that XML-RPC poses a threat or that disabling it is a solution.

"This tradeoff in pingback's design has been there for a decade now," he said via email. "It's seldom used outside of experimentation because it gets shut down by anti-spam providers like Akismet or web hosts when used at any scale, and there are cheaper, easier, and more effective ways to DDOS sites. That's why no serious attacks (above 2gbps) use it."

However, it's not the first time when Web security firms have reported DDoS attacks leveraging the WordPress pingback functionality. Security firm Incapsula reported that in July 2013 one of its customers was targeted in a pingback DDoS attack from 50,000 bots that generated a total of 8 million page hits at a rate of 1,000 hits per second.

Many Web application firewalls are likely to have detection and blocking rules for this type of attack already. The Sucuri blog post also contains a snippet of code that WordPress site owners can add to their themes to disable the pingback feature and prevent their sites from being misused in attacks.

Join the CSO newsletter!

Error: Please check your email address.

Tags online safetysecuritySucuriExploits / vulnerabilitiesIncapsula

Show Comments

Featured Whitepapers

Editor's Recommendations

Solution Centres

Stories by Lucian Constantin

Latest Videos

  • 150x50

    CSO Webinar: The Human Factor - Your people are your biggest security weakness

    ​Speakers: David Lacey, Researcher and former CISO Royal Mail David Turner - Global Risk Management Expert Mark Guntrip - Group Manager, Email Protection, Proofpoint

    Play Video

  • 150x50

    CSO Webinar: Current ransomware defences are failing – but machine learning can drive a more proactive solution

    Speakers • Ty Miller, Director, Threat Intelligence • Mark Gregory, Leader, Network Engineering Research Group, RMIT • Jeff Lanza, Retired FBI Agent (USA) • Andy Solterbeck, VP Asia Pacific, Cylance • David Braue, CSO MC/Moderator What to expect: ​Hear from industry experts on the local and global ransomware threat landscape. Explore a new approach to dealing with ransomware using machine-learning techniques and by thinking about the problem in a fundamentally different way. Apply techniques for gathering insight into ransomware behaviour and find out what elements must go into a truly effective ransomware defence. Get a first-hand look at how ransomware actually works in practice, and how machine-learning techniques can pick up on its activities long before your employees do.

    Play Video

  • 150x50

    CSO Webinar: Get real about metadata to avoid a false sense of security

    Speakers: • Anthony Caruana – CSO MC and moderator • Ian Farquhar, Worldwide Virtual Security Team Lead, Gigamon • John Lindsay, Former CTO, iiNet • Skeeve Stevens, Futurist, Future Sumo • David Vaile - Vice chair of APF, Co-Convenor of the Cyberspace Law And Policy Community, UNSW Law Faculty This webinar covers: - A 101 on metadata - what it is and how to use it - Insight into a typical attack, what happens and what we would find when looking into the metadata - How to collect metadata, use this to detect attacks and get greater insight into how you can use this to protect your organisation - Learn how much raw data and metadata to retain and how long for - Get a reality check on how you're using your metadata and if this is enough to secure your organisation

    Play Video

  • 150x50

    CSO Webinar: How banking trojans work and how you can stop them

    CSO Webinar: How banking trojans work and how you can stop them Featuring: • John Baird, Director of Global Technology Production, Deutsche Bank • Samantha Macleod, GM Cyber Security, ME Bank • Sherrod DeGrippo, Director of Emerging Threats, Proofpoint (USA)

    Play Video

  • 150x50

    IDG Live Webinar:The right collaboration strategy will help your business take flight

    Speakers - Mike Harris, Engineering Services Manager, Jetstar - Christopher Johnson, IT Director APAC, 20th Century Fox - Brent Maxwell, Director of Information Systems, THE ICONIC - IDG MC/Moderator Anthony Caruana

    Play Video

More videos

Blog Posts