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I'm working with a heavily obfuscated Autoit malware script and one of the major problems is that almost all variables and lines of code are obfuscated by a custom function.

The problem is that this custom function takes a long time to resolve and the code is only ever memory resident, either passed directly to execute or directly as arguments to other functions.

I was wondering whether it would be possible to programmatically replace all instances of strings containing encoded data with what all the functions actually resolve to.

I can't post any actual code from the script, but the obfuscated code and strings are all in the form of:

xor_deob_hex(decode_to_hex(decode("mixed_up_hex_literal", some_int_literal)), 
    decode_to_hex(decode("other_mixed_up_hex_literal, other_int_literal)

What I want is to remember the above string/code, evaluate the string/code, and replace all instances of the string/code with it's results within the original script. This way I can read the original code and determine the program's function.

Update: At this point I've moved on using API monitor because this particular process injects code into another process, but some pointers on code evaluation to replacement would still be useful.

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