CVE-2026-19735 Predictable TCP initial sequence numbers when the RFC 6528 secret key generation fails silently in the Zephyr TCP stack

The RFC 6528 initial-sequence-number implementation in subsys/net/ip/tcp.c derived every TCP ISN from SHA-256uniquekey || four-tuple plus a uptime-derived offset, where uniquekey is a 128-bit secret filled once by syscsrandget. The return value of that call was discarded and the once guard was...