# CVE-2026-89712

## Summary

- **CVE ID:** CVE-2026-89712
- **Severity:** CRITICAL
- **CVSS Score:** 9.8 (CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H)
- **CWE:** N/A
- **Published:** Sep 11, 2026
- **Last Modified:** Sep 14, 2026

## 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.

## Affected Products

- Linux — Linux (f4e44b393389c77958f7c58bf4415032b4cda15b)
- Linux — Linux (a4bc287943f5695209ff36bdc89f17b48d68fae7)
- Linux — Linux (5.10.220)
- Linux — Linux (5.14)
- Linux — Linux (0)
- Linux — Linux (6.12.109)
- Linux — Linux (6.18.50)
- Linux — Linux (7.2.4)
- Linux — Linux (7.3-rc1)
- Linux — Linux (5.10.270)
- Linux — Linux (5.15.221)
- Linux — Linux (6.1.188)
- Linux — Linux (6.6.157)

## References

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

## Exploitation Prediction (EPSS)

- **EPSS Score:** 0.70%
- **EPSS Percentile:** 51.7

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_Exported from OnDuty AI Vulnerability Intelligence on 2026-09-18._