Memory corruption via unchecked gcoap buffer copies

Buffer overflows in RIOT 2023.10 and earlier allow remote attackers to corrupt memory via crafted gcoap proxy input. gcoap_dns_server_proxy_get checks _uri length before copying _proxy with strcpy, while _gcoap_forward_proxy_copy_options copies an unchecked ETag length into a fixed-size buffer. Exploitation requires the affected gcoap paths and attacker-controlled input crossing a security boundary; consequences range from a crash to arbitrary code execution.