CVE-2025-21922 is a medium-severity vulnerability in the Linux kernel's ppp driver where a 2-byte header used with BPF socket filters is not fully initialized. This leads to an uninitialized value warning detected by Kernel Memory Sanitizer (KMSAN). The issue arises when carefully crafted BPF programs read uninitialized data, potentially causing kernel instability or crashes. The vulnerability does not impact confidentiality or integrity but affects availability. No affected versions or patches are explicitly stated in the input data.