A heap-based buffer overflow flaw was found in the SOCKS5 proxy handshake in the Curl package. If Curl is unable to resolve the address itself, it passes the hostname to the SOCKS5 proxy. However, the maximum length of the hostname that can be passed is 255 bytes. If the hostname is longer, then Curl switches to the local name resolving and passes the resolved address only to the proxy. The local variable that instructs Curl to "let the host resolve the name" could obtain the wrong value during a slow SOCKS5 handshake, resulting in the too-long hostname being copied to the target buffer instead of the resolved address, which was not the intended behavior.