RATDispenser – Stealthy JavaScript Loader Dispensing RATs

The initial JavaScript downloader is obfuscated and contains several eval functions.
One of the eval calls is a function that returns a long string, which is decoded by another function.
The function that decodes the string is located further down in the script.
At first sight it looks complicated, but it is a simple replacement function.
First, the passed arguments are stored in a new variable.
It is done this way to work correctly with an arbitrary number of arguments.
Next, the replacement operation runs on the initial string. The second argument of the replace function in JavaScript is another function which returns the replacement string.
In this case, the second argument to this inline function is the capturing group which matches the regular expression {d+}.
Since the capturing group is a decimal number, it is used as an index for the arguments array which is returned as a replacement string.
In case of an index out of bounds exception, the function returns the whole matching string, which was most likely implemented to handle mismatches.

To decode the string three arguments (A, u, F) are passed to the function.
The decoded string is Base64 encoded which can simply be decoded to analyze it in more detail. By creating and writing an ActiveX Data Stream Object this sequence is decoded and executed using an eval statement.

The most notable part of this sequence are the hex characters stored in a nested array, which is used as another layer of obfuscation.
Using an ActiveX object, a shell application instance is created, passing a long, chained argument.
By simply adding line breaks after the & characters, we can reformat the command line argument into a readable format.

The first parts of the command line argument are used to write lines to a VBScript file using an echo function. This file is then executed, resulting in a download through an XMLHTTP object.
The response to the GET request – the malware payload – is written to a file called YVC.JAR.
The VBScript file is then deleted. Afterwards, the cmd.exe process waits 12 seconds, before running the payload.

Sign Up For Threat Alerts

Threats Icon

Nov 29, 2021

IKEA email systems hit by ongoing cyberattack

IKEA is battling an ongoing cyberattack where threat actors are targeting employees in internal phishing...

Threats Icon

Nov 28, 2021

Tardigrade Malware targets Biomanufacturing Facilities

An advanced persistent threat (APT) has been linked to cyberattacks on two biomanufacturing companies that...

Threats Icon

Nov 24, 2021

Memento Team uses password-protected archives to bypass...

Calling themselves "Memento team", actors use Python-based ransomware that they reconfigured after setbacks. This was...

Threats Icon

Nov 23, 2021

Squirrelwaffle Exploits ProxyShell and ProxyLogon to Hijack...

Squirrelwaffle emerged as a new loader that is spread through spam campaigns. It is known...

Threats Icon

Nov 22, 2021

Emotet Returns

Back in January 2021, law enforcement and judicial authorities worldwide took down the Emotet botnet....

Threats Icon

Nov 18, 2021

Iranian Government-Sponsored APT Cyber Actors Exploiting Microsoft...

The Iranian government-sponsored APT actors are actively targeting a broad range of victims across multiple...

Threats Icon

Nov 17, 2021

Web compromises in the Middle East with...

ESET researchers have discovered strategic web compromise (aka watering hole) attacks against high-profile websites in...

Threats Icon

Nov 16, 2021

MosesStaff techniques: Ideology over Money

Hacker group MosesStaff began targeting Israeli organizations, joining a wave of attacks which was started...

Threats Icon

Nov 15, 2021

Lyceum mass backdoor attacks

Lyceum backdoors appear to have targeted ISPs and telecommunication operators in Israel, Morocco, Tunisia, and...

Threats Icon

Nov 14, 2021

New Golang malware (BotenaGo) targeting millions of...

Analysts have found new malware written in the open source programming language Golang. Deployed with...

Threats Icon

Nov 11, 2021

Fresh Variant of Snake Keylogger Malware

Snake Keylogger is a malware developed using .NET. It first appeared in late 2020 and...

Threats Icon

Nov 10, 2021

Mekotio Banker – Improved Stealth and Ancient...

A banking Trojan called "Mekotio" that targeted Latin America countries in the past, now making...

Threats Icon

Nov 09, 2021

Targeted Attack Campaign Against ManageEngine ADSelfService Plus...

US Cybersecurity and Infrastructure Security Agency (CISA) released an alert warning that advanced persistent threat...

Threats Icon

Nov 08, 2021

SquirrelWaffle Leverages malspam to deliver Qakbot

Recently, a new threat, referred to as "SquirrelWaffle" is being spread more widely via spam...

Threats Icon

Nov 08, 2021

ProxyShell exploitation leads to Babuk ransomware

A new threat actor is exploiting ProxyShell flaws in attacks aimed at Microsoft Exchange servers...