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.

External references:

https://justi.cz/security/2019/01/22/apt-rce.html