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A brand new stealthy JavaScript loader named RATDispenser is getting used to contaminate units with a wide range of distant entry trojans (RATs) in phishing assaults.
The novel loader was fast to determine distribution partnerships with no less than eight malware households, all designed to steal data and provides actors management over the goal units.
In 94% of the circumstances analyzed by the HP Menace Analysis crew, RATDispenser doesn’t talk with an actor-controlled server and is solely used as a first-stage malware dropper.
Going in opposition to the development of utilizing Microsoft Workplace paperwork to drop payloads, this loader makes use of JavaScript attachments, which HP discovered to have low detection charges.
An infection chain
The an infection begins with a phishing electronic mail containing a malicious JavaScript attachment named with a ‘.TXT.js’ double-extension. As Home windows hides extensions by default, if a recipient saves the file to their pc, it can seem as a innocent textual content file.
Phishing electronic mail with JS attachmentSource: HP
This textual content file is closely obfuscated to bypass detection by safety software program and shall be decoded when the file is double-clicked and launched.
As soon as launched, the loader will write a VBScript file to the %TEMP% folder, which is then executed to obtain the malware (RAT) payload.
Deobfuscated command-line argumentsSource: HP
These layers of obfuscation assist the malware evade detection 89% of the time, primarily based on VirusTotal scan outcomes.
“Though JavaScript is a much less widespread malware file format than Microsoft Workplace paperwork and archives, in lots of circumstances it’s extra poorly detected. From our set of 155 RATDispenser samples, 77 had been obtainable on VirusTotal which allowed us to research their detection charges,” defined the report by HP.
“Utilizing every pattern’s earliest scan consequence, on common the RATDispenser samples had been solely detected by 11% of accessible anti-virus engines, or eight engines in absolute numbers.”
Nonetheless, electronic mail gateways will detect the loader if the group has enabled the blocking of executable attachments, corresponding to .js, .exe, .bat, .com information.
One other method to cease the an infection chain from unfolding is to alter the default file handler for JS information, enable solely digitally signed scripts to run, or disable the WSH (Home windows Script Host).
Dropping malware
HP’s researchers had been capable of retrieve eight totally different malware payloads from RATDispenser within the final three months.
The recognized malware households are STRRAT, WSHRAT, AdWind, Formbook, Remcos, Panda Stealer, GuLoader, and Ratty.
In 10 out of the 155 samples analyzed, the loader established C2 communication to fetch second-stage malware, so whereas that is uncommon, the performance is there.
RATDispenser’s malware loading processSource: HP
In 81% of the malware drop circumstances, RATDispenser distributes STRRAT and WSHRAT (aka “Houdini), two highly effective credential stealers and keyloggers.
Panda Stealer and Formbook are the one two payloads to be all the time downloaded as a substitute of dropped.
Total, RATDispenser seems to accommodate the distribution of each outdated and new malware, serving as a flexible loader for risk actors of all talent ranges.
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