WordPress Vulnerability Affects A Quarter of the Internet

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A fresh vulnerability has been found affecting all versions of the WordPress and Drupal CMS platforms, as well as several Joomla extensions. It enables DDoS attacks that security experts say can’t be mitigated by traditional security measures.

Unfortunately, it casts a wide net, too: Incapsula estimates that the vulnerability endangers more than 250 million websites as a conservative guess, or more than 25% of the Internet website population today.

The vulnerability is of the “bomb” variety, using amplification methods, Incapsula noted:

XML-RPC is a popular Internet protocol used for cross-platform communication. Both WordPress and Drupal include XML-RPC in their core build, using it to execute remote API calls. The vulnerability exploits a loophole in XML-RPC parsing, using a method known as “entity expansion” to initiate amplified processing tasks. Together, these tasks can easily deplete large amounts of CPU and memory resources, resulting in latency and server downtime. In fact, using multiple calls, nested in a single XML document, an offender can deplete hundreds of megabytes of memory at a time.

Security researcher Nir Goldshlager, who first uncovered the issue, noted that it is a variant of known XML attacks.

“This phenomenon is predicated on a well-known cyber-attack, known as the XML Quadratic Blowup Attack,” he noted in an analysis. “This is starkly different from the customary XML bomb exploitation, in the sense that it distorts the Memory Limit and MySQL, and Apache Max Clients works. This bug can be utilized without the aid of any plugins, and it functions smoothly on the default installation of WordPress and Drupal.”

Further, it should be filed under “more bang for the buck”: Only one machine needed to exploit this vulnerability.

“Simply put, with a single device and a few hundred HTTP requests, an offender can bring down the most resilient of servers,” Incapsula explained. “The attack is similar to the Billion Laughs exploit. However, unlike Billion Laughs, this exploit doesn’t rely on recursion, which allows it to avoid existing countermeasures, used by XML parsers against heavily nested entities.”

It added, “Combined with the extremely large pool of targets and the high damage potential, this makes the exploit a triple threat – widespread, crippling and hard to weed out.”

WordPress and Drupal have already developed a patch, and CMS users are of course advised to apply it immediately.

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