WordPress patches amid huge spike in redirects to malware sites

US-CERT is urging WordPress admins update the publishing software after a recent spike in infected WordPress sites that redirect visitors to a dangerous exploit kit known as Nuclear.

WordPress released version 4.4.2 on Tuesday to address flaws that left instances vulnerable to an “open redirection attack” bug and a “possible” Server Side Request Forgery (SSRF).

Open redirects are a lingering problem for web applications, and as the name suggests rely on exploiting a vulnerable web page to redirect a visitor to an malicious page. They’re often accompanied by a phishing attack, security firm Qualys recently explained.

WordPress remains one of the more popular publishing platforms on the web and installations have in the past been abused to spread malware, which is likely why US-CERT urged admins to upgrade as soon as possible to version 4.4.2.

The security update may help explain a mysterious spike in WordPress infections. Just a day before WordPress’ patch, security firm Securi warned of a rash of WordPress sites that had been infected with malware appended to legitimate JavaScript files. WordPress sites were being reinfected even after removing the malware, it noted.

Security firm Malwarebytes followed up that report noting that the infected WordPress sites were in fact redirecting visitors to pages hosting fraudulent ads that ultimately flicked them to a secondary site that hosted Nuclear— a nasty exploit that serves up a smorgasbord of threats, including the CryptoWall 4.0 file-encrypting malware.

“WordPress sites are injected with huge blurbs of rogue code that performs a silent redirection to domains appearing to be hosting ads. This is a distraction (and fraud) as the ad is stuffed with more code that sends visitors to the Nuclear Exploit Kit,” explained Jerome Segura, senior security researcher at Malwarebytes.

Denis Sinegubko, a senior malware researcher with Securi, said the malware only infected first time visitors to an infected site. Meanwhile, WordPress admins would have found that they’re web server will continuously be reinfected even after attempting to clean up the malware.

The malware is particularly troublesome for WordPress users that host several domains on the same hosting account since it attempts to infect all accessible JavaScript files.

“It’s not enough to clean just one site (e.g. the one you care about) or all but one (e.g. you don’t care about a test or backup site) in such situations – an abandoned site will be the source of the reinfection. In other words, you either need to isolate every sites or clean/update/protect all of them at the same time,” he said.

In any case, if WordPress admins haven’t already updated their software, this attack should give them cause to do so.

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