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CVE-2025-21696 is a Linux kernel memory-management vulnerability caused by incomplete clearing of userfaultfd write-protection state during mremap(). When a write-protected memory region is remapped without UFFD_FEATURE_EVENT_REMAP enabled, the VM_UFFD_WP flag is cleared from the virtual memory area while corresponding PTE/PMD write-protection state can remain set. A subsequent mprotect(PROT_WRITE) can make a page-table entry writable while its userfaultfd write-protection flag remains set, triggering a warning in page_table_check_pte_flags(). The correction clears logical write-protection state across ordinary PTE, swap-PTE, PTE-marker, huge-PMD, and hugetlb paths.
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6 sources tracked across advisories, community write-ups, and news. New activity surfaces here as Mallory finds it.
A Linux kernel memory-management flaw leaves userfaultfd write-protection flags inconsistent after mremap(). A subsequent mprotect(PROT_WRITE) can trigger a page-table-check warning. The advisory rates it medium severity, with CVSS v3 5.5, describing local exploitation requiring low privileges and high availability impact, with no confidentiality or integrity impact. The fix consistently clears uffd-wp state across PTE, huge PMD, and hugetlb paths.
Linux kernel userfaultfd write-protect page-table-state handling flaw on mremap.
A Linux kernel memory-management flaw involving inconsistent userfaultfd write-protection state after mremap(). The affected Google COS sys-kernel/csql-kernel-6_6 package is remediated in version 19165.0.0 or later.
Linux kernel memory-management UFFD write-protect state flaw.
Query your assets running an affected version, and investigate the blast radius.
Every observed campaign linking this CVE to a named adversary.
Malware families riding this exploit, with evidence and IOCs.
YARA, Sigma, Snort, and vendor rules, auto-deployed to your SIEM.
Cross-references every affected SKU, including bundled OEM variants.
Community discussion across Reddit, Mastodon, and other social sources.