tcp_emu in tcp_subr.c in libslirp 4.1.0, as used in QEMU 4.2.0, mismanages
memory, as demonstrated by IRC DCC commands in EMU_IRC. This can cause a
heap-based buffer overflow or other out-of-bounds access which can lead to
a DoS or potential execute arbitrary code.

It was discovered that the SLiRP networking implementation of the QEMU
emulator did not properly manage memory under certain circumstances. An
attacker could use this to cause a heap-based buffer overflow or other
out-of-bounds access, which can lead to a denial of service (application
crash) or potential execute arbitrary code.

mdeslaur

possible better approach would be to disable tcp_emu completely https://gitlab.freedesktop.org/slirp/libslirp/commit/07c2a44b67e219ac14207f7a1b33704e1312cf91