models/metadata.py in the pikepdf package 1.3.0 through 2.9.2 for Python allows XXE when parsing XMP metadata entries.
https://github.com/pikepdf/pikepdf/commit/3f38f73218e5e782fe411ccbb3b44a793c0b343a
https://github.com/pikepdf/pikepdf/blob/v2.10.0/docs/release_notes.rst#v2100