CVE-2026-44327 affects free5GC, an open-source 5G core network implementation. Prior to version 4.2.2, the Network Exposure Function (NEF) component mounts the nnef-oam route group without proper OAuth2/bearer-token authorization. This allows network attackers who can reach the NEF on the Service Based Interface (SBI) to access OAM routes without any authorization headers. The vulnerability affects the entire OAM route group, meaning future operations added to this group would inherit the missing authentication boundary by default. While the current OAM handler is just a stub returning null, this represents a significant structural security defect. The issue has been resolved in version 4.2.2.