Modern networks impose few restrictions on packet creation, allowing anyone to craft packets with arbitrary header values. This technique, known as spoofing, enables attackers to send traffic that appears to originate from other sources.
TCP includes built-in security features, but its effectiveness relies on the quality of the Pseudo Random Number Generator (PRNG) used; if an attacker can predict the sequence numbers, they may compromise TCP security through spoofed communications.
While TCP provides some resilience against spoofing, protocols like UDP and ICMP do not have similar protections. Spoofing packets typically requires root or system-level privileges, as operating systems enforce communication standards via APIs that adhere to RFC (Request For Comments) specifications, making it difficult for attackers to craft custom packets without elevated privileges.