skops' MethodNode can access unexpected object fields through dot notation, leading to arbitrary code execution at load time

skops is a Python library which helps users share and ship their scikit-learn based models. Versions 0.11.0 and below contain an inconsistency in MethodNode, which can be exploited to access unexpected object fields through dot notation. This can be used to achieve arbitrary code execution at load time. While this issue may seem similar to GHSA-m7f4-hrc6-fwg3, it is actually more severe, as it relies on fewer assumptions about trusted types. This is fixed in version 12.0.0.