CVE-2025-21894 is a vulnerability in the Linux kernel's ENETC driver where Virtual Functions (VFs) do not support the HWTSTAMP_TX_ONESTEP_SYNC hardware timestamping feature. Attempting to use one-step timestamping on VFs causes a kernel crash due to improper access to PMa_SINGLE_STEP registers, which are only accessible by the Physical Function (PF). This results in a kernel paging fault and system instability.