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Malwrologist @DissectMalware
, 6 tweets, 6 min read Read on Twitter
#linux #bash #obfuscation using shell parameter expansion:

${alphabet:2:1}at really
${alphabet: -24:-23}at really
${alphabet: -24:1}at really
${alphabet:2:-23}at really…
similar #bat #windows (…)
The goal is to obfuscate the following command:
cat really
in which, really is a file.
Using arithmetic (add, sub, mul, div, mod, and pow) for calculating index or lenght
${alphabet: 2:(-20-3)}at really
what about a #null character? (my #fav)
${alphabet: 2:1}${alphabet: -n:-n}at really
${alphabet: 2:1}${alphabet: n:0}at really
*where n is a positive number

${alphabet: 2:1}${alphabet: x:y}at really
*where (x,y) are out of range
To make it worse:
numbers in bash can be represented in various forms
for example number 10 is:
10 #decimal
012 #octal
0xa 0Xa #hexadecimal
2#1010 base#number #binary

* leading zeros are ignored

#bash #arithmetic #expansion for #obfuscation
example: #ipaddr
goal: #ping is 134744072
ping $((32#40G208))
ping $((32#40G1VU+16#a))
ping $((32#40G1VU+16#9+13#1))

Repr IP with num mentioned by others:
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