CVE-2026-89712: Red Hat restart ssc_expire_umount walk after dropping nfsd_ssc_lock
This Red Hat advisory covers CVE-2026-89712 in Red Hat Enterprise Linux 10, Red Hat Enterprise Linux 6 and Red Hat Enterprise Linux 9.
Key facts
- Vendor rating
- High, CVSS 7
- CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H· base score 9.8, scored by LinuxAttack vector: network. Attack complexity: low. Privileges required: none. User interaction: none. Scope: unchanged. Confidentiality impact: high. Integrity impact: high. Availability impact: high.- EPSS
- 0.71% chance of exploitation in the next 30 days (54th percentile). FIRST EPSS, .
- CISA KEV
- Not listed (catalogue checked )
- Source published
- Source revised
- Listed by VulniPulse
Compiled by VulniPulse from the linked sources. How records are collected and checked.
Affected products & platforms
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. A flaw was found in the Linux kernel's Network File System Daemon (NFSD) component.
Text from the source record.
CVE-2026-89712 in other vendors' advisories
- NetApp: NTAP-20261002-0016, critical severity
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