Attack wrangles thousands of web users into a password

const getTaskUrl = 'hxxps://dynamic-linx[.]com/getTask.php';
const completeTaskUrl = 'hxxps://dynamic-linx[.]com/completeTask.php';
…

[871,"https://REDACTED","redacted","60","junkyard","johncena","jewish","jakejake","invincible","intern","indira","hawthorn","hawaiian","hannah1","halifax","greyhound","greene","glenda","futbol","fresh","frenchie","flyaway","fleming","fishing1","finally","ferris","fastball","elisha","doggies","desktop","dental","delight","deathrow","ddddddd","cocker","chilly","chat","casey1","carpenter","calimero","calgary","broker","breakout","bootsie","bonito","black123","bismarck","bigtime","belmont","barnes","ball","baggins","arrow","alone","alkaline","adrenalin","abbott","987987","3333333","123qwerty","000111","zxcv1234","walton","vaughn","tryagain","trent","thatcher","templar","stratus","status","stampede","small","sinned","silver1","signal","shakespeare","selene","scheisse","sayonara","santacruz","sanity","rover","roswell","reverse","redbird","poppop","pompom","pollux","pokerface","passions","papers","option","olympus","oliver1","notorious","nothing1","norris","nicole1","necromancer","nameless","mysterio","mylife","muslim","monkey12","mitsubishi"]

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

Sinegubko wrote:

Attack stages and lifecycle

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.

• Stage 1: Obtain URLs of WordPress sites. The attackers either crawl the Internet themselves or use various search engines and databases to obtain lists of target WordPress sites.
• Stage 2: Extract author usernames. Attackers then scan the target sites, extracting real usernames of authors that post on those domains.
• Stage 3: Inject malicious scripts. Attackers then inject their dynamic-linx[.]com/chx.js script to websites that they have already compromised.
• Stage 4: Brute force credentials. As normal site visitors open infected web pages, the malicious script is loaded. Behind the scenes, the visitors’ browsers conduct a distributed brute force attack on thousands of target sites without any active involvement from attackers.
• Stage 5: Verify compromised credentials. Bad actors verify brute forced credentials and gain unauthorized access to sites targeted in stage 1.

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.

Distributed brute force attack steps:

1. When a site visitor opens an infected web page, the user’s browser requests a task from the hxxps://dynamic-linx[.]com/getTask.php URL.
2. If the task exists, it parses the data and obtains the URL of the site to attack along with a valid username and a list of 100 passwords to try.
3. For every password in the list, the visitor’s browser sends the wp.uploadFile XML-RPC API request to upload a file with encrypted credentials that were used to authenticate this specific request. That’s 100 API requests for each task! If authentication succeeds, a small text file with valid credentials is created in the WordPress uploads directory.
4. When all the passwords are checked, the script sends a notification to hxxps://dynamic-linx[.]com/completeTask.php that the task with a specific taskId (probably a unique site) and checkId (password batch) has been completed.
5. Finally, the script requests the next task and processes a new batch of passwords. And so on indefinitely while the infected page is open.

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.