CVE-2026-89711: Linux Vulnerability (CVSS 8.2)

Description

In the Linux kernel, the following vulnerability has been resolved: NFSD: remove flawed WARN_ON_ONCE from nfsd_mode_check The header for commit e75b23f9e323 ("nfsd: check d_can_lookup in fh_verify of directories") details the assumption that justified adding the WARN_ON_ONCE to nfsd_mode_check(), that assumption is invalid (in the case of NFS reexport). When NFSD exports an NFS filesystem it is very possible for nfsd_mode_check() to encounter a @dentry that doesn't have i_op->lookup (see nfs_fhget()'s NFS_ATTR_FATTR_MOUNTPOINT and NFS_ATTR_FATTR_V4_REFERRAL handling, and d_flags_for_inode()). So remove nfsd_mode_check()'s WARN_ON_ONCE(). The nfserr_notdir return on that branch must stay. It guards the subsequent lookup_one_unlocked() -> __lookup_slow() path, which calls inode->i_op->lookup() with no NULL check, so returning nfserr_notdir is what keeps a client LOOKUP into such a @dentry from dereferencing a NULL method pointer.

Metrics

CVSS 3.1

8.2/10

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

EPSS Probability

0.40%

33.9th 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	>= e75b23f9e323b1e0759619c39d5a9f7a3a5d9d2c, < ae251937c6f0237e5b555a5e4ba4595b8206e865; >= e75b23f9e323b1e0759619c39d5a9f7a3a5d9d2c, < e145e8d67a5d41c72d322e7f87ab474d39d9dfb7; >= e75b23f9e323b1e0759619c39d5a9f7a3a5d9d2c, < 9f4434893a2783f7384d993cea883aff3fb7a52d; >= e75b23f9e323b1e0759619c39d5a9f7a3a5d9d2c, < 2ef131323999539038e306773c8256403834361b; >= e75b23f9e323b1e0759619c39d5a9f7a3a5d9d2c, < b55b4d880bb080fa10eb08ba21a5d8679b8102fe; >= e75b23f9e323b1e0759619c39d5a9f7a3a5d9d2c, < 7ef182a8fe9c12b0d936880b1e504840639aa009; >= e75b23f9e323b1e0759619c39d5a9f7a3a5d9d2c, < a275de3bac5635514ca830f2e46b5ff0e66b5c4c; >= e75b23f9e323b1e0759619c39d5a9f7a3a5d9d2c, < aa0cf48a448c5a9fe1a1e880899ecd589ce39e6e
Linux	Linux	4.8

References

Timeline

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

Frequently Asked Questions

What is CVE-2026-89711?

In the Linux kernel, the following vulnerability has been resolved: NFSD: remove flawed WARN_ON_ONCE from nfsd_mode_check The header for commit e75b23f9e323 ("nfsd: check d_can_lookup in fh_verify of directories") details the assumption that justified adding the WARN_ON_ONCE to nfsd_mode_check(), that assumption is invalid (in the case of NFS reexport). When NFSD exports an NFS filesystem it is very possible for nfsd_mode_check() to encounter a @dentry that doesn't have i_op->lookup (see nfs_fhget()'s NFS_ATTR_FATTR_MOUNTPOINT and NFS_ATTR_FATTR_V4_REFERRAL handling, and d_flags_for_inode()). So remove nfsd_mode_check()'s WARN_ON_ONCE(). The nfserr_notdir return on that branch must stay. It guards the subsequent lookup_one_unlocked() -> __lookup_slow() path, which calls inode->i_op->lookup() with no NULL check, so returning nfserr_notdir is what keeps a client LOOKUP into such a @dentry from dereferencing a NULL method pointer.

How severe is CVE-2026-89711?

CVE-2026-89711 has a CVSS score of 8.2/10 (HIGH severity). The EPSS model estimates a 0.40% probability of exploitation in the next 30 days.

How do I fix CVE-2026-89711?

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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