CVE-2025-21637 is a vulnerability in the Linux kernel SCTP sysctl udp_port handling where the use of current->nsproxy can lead to a null pointer dereference. This occurs because current->nsproxy may be NULL when the current task is exiting, causing a kernel 'Oops'. The issue was identified by syzbot and fixed by changing the code to obtain the 'net' structure from table->data instead of current->nsproxy.