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Arthur T Knackerbracket [soylentnews.org] writes:

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Arthur T Knackerbracket has processed the following story [arstechnica.com]:

Attackers have transformed hundreds of hacked sites running WordPress software into command-and-control servers that force visitors’ browsers to perform password-cracking attacks.

A web search [publicwww.com] for the JavaScript that performs the attack showed it was hosted on 708 sites at the time this post went live on Ars, up from 500 two days ago. Denis Sinegubko, the researcher who spotted the campaign, said at the time that he had seen thousands of visitor computers running the script, which caused them to reach out to thousands of domains in an attempt to guess the passwords of usernames with accounts on them.

“This is how thousands of visitors across hundreds of infected websites unknowingly and simultaneously try to bruteforce thousands of other third-party WordPress sites,” Sinegubko wrote [sucuri.net]. “And since the requests come from the browsers of real visitors, you can imagine this is a challenge to filter and block such requests.”

Like the hacked websites hosting the malicious JavaScript, all the targeted domains are running the WordPress content management system. The script—just 3 kilobits in size—reaches out to an attacker-controlled getTaskURL, which in turn provides the name of a specific user on a specific WordPress site, along with 100 common passwords. When this data is fed into the browser visiting the hacked site, it attempts to log into the targeted user account using the candidate passwords. The JavaScript operates in a loop, requesting tasks from the getTaskURL reporting the results to the completeTaskURL, and then performing the steps again and again.

A snippet of the hosted JavaScript appears below, and below that, the resulting task:

With 418 password batches as of Tuesday, Sinegubko has concluded the attackers are trying 41,800 passwords against each targeted site.

Sinegubko wrote:

The attack consists of five key stages that allow a bad actor to leverage already compromised websites to launch distributed brute force attacks against thousands of other potential victim sites.

So, how do attackers actually accomplish a distributed brute force attack from the browsers of completely innocent and unsuspecting website visitors? Let’s take a look at stage 4 in closer detail.

As of Tuesday, the researcher had observed “dozens of thousands of requests” to thousands of unique domains that checked for files uploaded by the visitor browsers. Most files reported 404 web errors, an indication that the login using the guessed password failed. Roughly 0.5 percent of cases returned a 200 response code, leaving open the possibility that password guesses may have been successful. On further inspection, only one of the sites was compromised. The others were using non-standard configurations that returned the 200 response, even for pages that weren’t available.

Over a four-day span ending Tuesday, Sinegubko recorded more than 1,200 unique IP addresses that tried to download the credentials file. Of those, five addresses accounted for over 85 percent of the requests:

Last month, the researcher observed one of the addresses—87.121.87.178—hosting a URL used in a cryptojacking attack [sucuri.net]. One possibility for the change is that the earlier campaign failed because the malicious URL it relied on wasn’t hosted on enough hacked sites and, in response, the same attacker is using the password-cracking script in an attempt to recruit more sites.

As Sinegubko notes, the more recent campaign is significant because it leverages the computers and Internet connections of unwitting visitors who have done nothing wrong. One way end users can stop this is to use NoScript or another tool that blocks JavaScript from running on unknown sites. NoScript breaks enough sites that it’s not suitable for less experienced users, and even those with more experience often find the hassle isn’t worth the benefit. One other possible remedy is to use certain ad blockers.

Original Submission