CVE-2026-89712: Linux Vulnerability (CVSS 9.8)

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.

Metrics

CVSS 3.1

9.8/10

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

EPSS Probability

0.63%

48.1th percentile

Probability of exploitation in the next 30 days. Learn more

Affected Software

Source: CNA advisory (CVE.org). NVD analysis pending.

Vendor	Product	Versions
Linux	Linux	>= a4bc287943f5695209ff36bdc89f17b48d68fae7, < 2b59029b8f24a99b5d844af2da3950d39d36eeea; >= f4e44b393389c77958f7c58bf4415032b4cda15b, < d9e151fea5ed706c1284adacabd869b0be745db2; >= f4e44b393389c77958f7c58bf4415032b4cda15b, < 659ee3da073164e1e6e40dfcbc26eeed85845f93; >= f4e44b393389c77958f7c58bf4415032b4cda15b, < 60680ae7243b22de3d09be990d8e23bcfc4af837; >= f4e44b393389c77958f7c58bf4415032b4cda15b, < 77de363d9a1c8cd35f20482782c612cda085791a; >= f4e44b393389c77958f7c58bf4415032b4cda15b, < 4ed8d2317aef21cc2a9e5a55d6b59860b4b151a8; >= f4e44b393389c77958f7c58bf4415032b4cda15b, < 7377fa964b8aaf47cb04e5efcc4c82d15e8c2ce9; >= f4e44b393389c77958f7c58bf4415032b4cda15b, < 036c1b182f4da65363e79ec0ac276edc6b7296e5; >= 5.10.220, < 5.10.270
Linux	Linux	5.14

References

Timeline

Published: Sep 11, 2026
Last Modified: Sep 14, 2026
Status: Received

Frequently Asked Questions

What is CVE-2026-89712?

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.

How severe is CVE-2026-89712?

CVE-2026-89712 has a CVSS score of 9.8/10 (CRITICAL severity). The EPSS model estimates a 0.63% probability of exploitation in the next 30 days.

How do I fix CVE-2026-89712?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

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