This flaw makes curl overflow a heap based buffer in the
SOCKS5 proxy handshake. When curl is asked to pass along
the hostname to the SOCKS5 proxy to allow that to resolve
the address instead of it getting done by curl itself, the
maximum length that hostname can be is 255 bytes. If the
hostname is detected to be longer than 255 bytes, curl
switches to local name resolving and instead passes on the
resolved address only to the proxy. Due to a bug, the
local variable that means "let the host resolve the name"
could get the wrong value during a slow SOCKS5 handshake,
and contrary to the intention, copy the too long hostname
to the target buffer instead of copying just the resolved
address there.