QEMU 4.1.0 has a memory leak in zrle_compress_data in ui/vnc-enc-zrle.c during a VNC disconnect operation because libz is misused, resulting in a situation where memory allocated in deflateInit2 is not freed in deflateEnd.
https://lists.debian.org/debian-lts-announce/2020/07/msg00020.html
https://usn.ubuntu.com/4372-1/