The kantan netprint App for Android 2.0.3 and earlier does not verify X.509 certificates from servers, which allows man-in-the-middle attackers to spoof servers and obtain sensitive information via a crafted certificate.
http://jvn.jp/en/jp/JVN66435380/index.html
https://www.printing.ne.jp/support/information/AppVulnerability.html
https://cve.mitre.org/cgi-bin/cvename.cgi?name=CVE-2020-5522