Incorrect sanitation of the 302 redirect field in HTTP transport method of apt versions 1.4.8 and earlier can lead to content injection by a MITM attacker, potentially leading to remote code execution on the target machine.
https://www.debian.org/security/2019/dsa-4371
https://usn.ubuntu.com/3863-2/
https://usn.ubuntu.com/3863-1/