CVE-2026-44321 affects free5GC, an open-source 5G core network implementation. Prior to version 4.2.2, the SMF component mounts the UPI management route group without OAuth2 middleware protection. An unauthenticated attacker can send a POST request to /upi/v1/upNodesLinks with malicious JSON that triggers validation failures in UpNodesFromConfiguration(). One attack path involves creating UPF pools that overlap with existing pools, causing the entire SMF process to terminate with exit code 1. This vulnerability allows for denial of service attacks against 5G network infrastructure through a single unauthenticated request. The issue has been fixed in version 4.2.2.