CVE-2025-21696

Summary

CVE-2025-21696 is a vulnerability affecting the Linux kernel. It involves an inconsistency between virtual memory area (vma) flags and page table entry/page massive (PTE/PMD) flags during a memory remapping operation using mremap(). Specifically, when remapping a write-protected memory region without the UFFD_FEATURE_EVENT_REMAP feature, the uffd-wp flag is cleared in the vma but not in the corresponding PTE/PMD. This discrepancy results in a warning being triggered when attempting to set the PTE to writable, even though uffd-wp is still set. The issue has been addressed by explicitly clearing the uffd-wp flag in PTEs, PMDs, and huge PTEs during mremap() operations.

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