YAML: code execution using !!python/object

Published: 19 February 2019
on channel: KacperSzurekEN

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A popular opinion says to not use the pickle class on a data given by user because on deserialization it may lead to the object injection attack and malicious code execution.
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But what about other formats? Are they also dangerous?
My name is Kacper Szurek and in today's episode of "from 0 to pentesting hero" I'm going to talk about yaml files.

Yaml format is not as simple as it might seem.
In the standard parser used in Python, we can also use the apply tag, which allows you to call any function from any module, and pass appropriate parameters to them.

So it is equivalent to the ability to execute arbitrary code on the server that we attack.
In our case, we will use the os.system function to list the contents of the current directory.

Twitter: / kacperszurek
Website: https://security.szurek.pl/
Github: https://github.com/kacperszurek/

#from0topentestinghero #bugbounty #python

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