cve 2025 21696

CVE-2025-21696 is a Linux kernel vulnerability affecting the memory management subsystem, specifically the interaction between userfaultfd (uffd) write-protect tracking and the mremap system call. The bug causes inconsistent clearing of the uffd-wp PTE/PMD state during memory remapping, which can lead to kernel warnings, oopses, and denial-of-service conditions. The issue is described upstream as "mm: clear uffd-wp PTE/PMD state on mremap." This tag covers discussions about the vulnerability's technical details, impact, and available patches. While the vulnerability is in the Linux kernel, it may affect Windows systems running Linux virtual machines or Windows Subsystem for Linux (WSL) environments.