Peppol-py before 1.1.1 allows XXE attacks because of the Saxon configuration. When validating XML-based invoices, the XML parser could read files from the filesystem and expose their content to a remote host.
https://github.com/iterasdev/peppol-py/releases/tag/1.1.1
https://github.com/iterasdev/peppol-py/pull/16
https://github.com/iterasdev/peppol-py/commit/349a4bff8adb6205ea411bac8d7a06da0477abd7