tftp.c in libslirp 4.1.0, as used in QEMU 4.2.0, does not prevent ..\ directory traversal on Windows.
https://security-tracker.debian.org/tracker/CVE-2020-7211
https://gitlab.freedesktop.org/slirp/libslirp/commit/14ec36e107a8c9af7d0a80c3571fe39b291ff1d4