SANS ISC: Ransomware in Node.js

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SANS ISC InfoSec Forums

Happy new year to all! I hope that you enjoyed the switch to 2020! From a security point of view, nothing changed and malicious code never stops trying to abuse our resources even during the holiday season. Here is a sample that I spotted two days ago. It’s an interesting one because it’s a malware that implements ransomware features developed in Node.js[1]! The stage one is not obfuscated and I suspect the script to be a prototype or a test… It has been submitted to VT from Bahrein (SHA256:90acae3f682f01864e49c756bc9d46f153fcc4a7e703fd1723a8aa7ec01b378c) and has currently a score of 12/58[2].

The first stage is a VBScript that decodes the ransomware, setup persistence and deploys a local Node.js instance running the generated files in %USERPROFILE%\AppData\Local:

\GFp0JAk\lLT8PCI.js
\GFp0JAk\node_modules\graceful-fs\fs.js
\GFp0JAk\node_modules\graceful-fs\package.json
\GFp0JAk\node_modules\graceful-fs\graceful-fs.js
\GFp0JAk\node_modules\graceful-fs\legacy-streams.js
\GFp0JAk\node_modules\graceful-fs\polyfills.js

Node.js is downloaded from hxxps://nodejs[.]org/download/release/latest-v8.x/win-x86/node.exe and saved as %USERPROFILE%\AppData\Local\GFp0JAk\GFp0JAk.exe

Persistence is added via Registry keys:

oShell.RegWrite "HKCU\Software\Microsoft\Windows\CurrentVersion\Run\Microsoft Office", "wscript " & strVbs,"REG_SZ"
oShell.RegWrite "HKCU\Software\Microsoft\Windows\CurrentVersion\Run\Startup",  strExe & " " & outWorkingDir & "\" & strEntPoint & " decryptStatic","REG_SZ"
oShell.RegWrite "HKCU\Software\Microsoft\Windows\CurrentVersion\Run\Windows", "cmd /c start  /min " & outWorkingDir & "\How-to-buy-bitcoins.html","REG_SZ"

The script main loop performs the following tasks every 40 seconds:

1. Checks if node.exe has been successfully downloaded and, if not, it downloads and dumps it to the disk
2. Dumps the Node.js module and files to disk (see the list above)
3. Deploys the Node.js code.

Once done, an “initdone” file is created and the desktop layout reset (icons & positions) by deleting the registry key:

HKCU\Software\Microsoft\Windows\Shell\Bags\1\Desktop

Now, let’s have a look at the Node.js code, the ransomware itself.

This code is obfuscated but easy to process with a Javascript beautifier. Here is some interesting extracted information:

Ransom price: 0.4 BTC
Bitcoin wallet: 18aBKwKJvMCkZmpkcCbW9b9y9snAmU3kgo[3]

Encryption is performed via a public/private key pair.

Files to encrypt are scanned via this function:

scan = function() {
    var b = [];
    b.push(userprofile + ""\\
        Desktop "");
    b.push(userprofile + ""\\
        Documents "");
    b.push(userprofile + ""\\
        Downloads "");
    b.push(userprofile + ""\\
        Contacts "");
    b.push(userprofile + ""\\
        Pictures "");
    b.push(userprofile + ""\\
        Music "");
    b.push(userprofile + ""\\
        Videos "");
    b.push(userprofile + ""\\
        AppData\\ Local\\ Microsoft\\ Outlook "");
    for (var a = 0; 25 > a; a++) {
        var c = String.fromCharCode(66 + a) + "": "",
            d = c + ""\\
        "" + testFile;
        if (fs.existsSync(c)) try {
            fs.writeFileSync(d, ""
                "", ""
                utf - 8 ""), b.push(c), removeFile(d)
        } catch (e) {}
    }
    return b
};

The ransomware notification is also generated on the fly:

I did not find a contact email address for the victims and the encrypted file extension is empty in the code. If you have more information about this sample, please share it!

[1] https://nodejs.org/en/
[2] https://www.virustotal.com/gui/file/90acae3f682f01864e49c756bc9d46f153fcc4a7e703fd1723a8aa7ec01b378c/detection
[3] https://www.blockchain.com/btc/address/18aBKwKJvMCkZmpkcCbW9b9y9snAmU3kgo

Xavier Mertens (@xme)
Senior ISC Handler - Freelance Cyber Security Consultant
PGP Key