I don't know. Something like a Python pickle file where parsing is unavoidable.

On a second read, I realized a format problem was unlikely, but the headline just said, "Apache Parquet". My mind might the same conclusion if it said "safetensors" or "PNG".

That data had to be encoded in a certain way which would lead to unavoidable exploitation in every conforming implementation. For example, PDF permits embedded JavaScript and… that has not gone well.

Macros in old Microsoft Word documents were quite a popular attack.