Max Justicz discovered a vulnerability in APT, the high level package manager. The code handling HTTP redirects in the HTTP transport method doesn’t properly sanitize fields transmitted over the wire. This vulnerability could be used by an attacker located as a man-in-the-middle between APT and a mirror to inject malicous content in the HTTP connection. This content could then be recognized as a valid package by APT and used later for code execution with root privileges on the target machine.

https://lists.debian.org/debian-security-announce/2019/msg00010.html