userfaultfd

About this tag
The userfaultfd tag on WindowsForum.com covers Linux kernel vulnerabilities and patches related to the userfaultfd subsystem, a mechanism for user-space page fault handling. Recent discussions focus on CVE-2025-21696, a bug where mremap fails to clear uffd-wp PTE/PMD state, leading to kernel warnings and denial-of-service. Another thread addresses CVE-2025-40040, a flag-dropping bug in the KSM madvise path that can inadvertently clear userfaultfd flags from VMA vm_flags, causing oopses. Both issues are correctness bugs requiring kernel patching for stability. The tag is relevant for Linux system administrators and developers working with memory management, userfaultfd, and kernel security.

  1. CVE-2025-21696: Linux Kernel uffd_wp mremap Bug and Patch Guide

    The Linux kernel vulnerability tracked as CVE-2025-21696 — described upstream as “mm: clear uffd-wp PTE/PMD state on mremap” — is a correctness bug in the kernel’s memory-management paths that can produce kernel warnings, oopses, and denial-of-service conditions when specific userfaultfd and...
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    • cve 2025 21696 linux kernel memory management userfaultfd
    • Replies: 0
    • Forum: Security Alerts

  2. Linux Kernel Patch Fixes KSM Madvise Flag Bug (CVE-2025-40040)

    The Linux kernel patch addressing CVE-2025-40040 fixes a subtle but consequential flag-dropping bug in the KSM madvise path: under specific 64-bit builds a bitwise operation in ksm_madvise could inadvertently clear the upper 32 bits of a VMA’s vm_flags, removing userfaultfd (UFFD) flags and...