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.

CVSS v3 8.2 HIGH

8.2^/10

CVSS v3 : HIGH

Vector :

Exploitability : 3.9 / Impact : 4.2

Attack Vector NETWORK

Attack Complexity LOW

Privileges Required NONE

User Interaction NONE

Confidentiality Impact LOW

Integrity Impact NONE

Availability Impact HIGH

Scope UNCHANGED

References

Link	Resource
https://git.kernel.org/stable/c/2ef131323999539038e306773c8256403834361b
https://git.kernel.org/stable/c/7ef182a8fe9c12b0d936880b1e504840639aa009
https://git.kernel.org/stable/c/9f4434893a2783f7384d993cea883aff3fb7a52d
https://git.kernel.org/stable/c/a275de3bac5635514ca830f2e46b5ff0e66b5c4c
https://git.kernel.org/stable/c/aa0cf48a448c5a9fe1a1e880899ecd589ce39e6e
https://git.kernel.org/stable/c/ae251937c6f0237e5b555a5e4ba4595b8206e865
https://git.kernel.org/stable/c/b55b4d880bb080fa10eb08ba21a5d8679b8102fe
https://git.kernel.org/stable/c/e145e8d67a5d41c72d322e7f87ab474d39d9dfb7

Configurations

No configuration.

History

No history.

Information

Published : 2026-09-11 20:19

Updated : 2026-09-14 13:19

NVD link : CVE-2026-89711

Mitre link : CVE-2026-89711

CVE.ORG link : CVE-2026-89711

JSON object : View

Products Affected

No product.

CWE

No CWE.

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"https://git.kernel.org/stable/c/ae251937c6f0237e5b555a5e4ba4595b8206e865", "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"}, {"url": "https://git.kernel.org/stable/c/b55b4d880bb080fa10eb08ba21a5d8679b8102fe", "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"}, {"url": "https://git.kernel.org/stable/c/e145e8d67a5d41c72d322e7f87ab474d39d9dfb7", "source": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"}], "vulnStatus": "Received", "descriptions": [{"lang": "en", "value": "In the Linux kernel, the following vulnerability has been resolved:\n\nNFSD: remove flawed WARN_ON_ONCE from nfsd_mode_check\n\nThe header for commit e75b23f9e323 (\"nfsd: check d_can_lookup in\nfh_verify of directories\") details the assumption that justified\nadding the WARN_ON_ONCE to nfsd_mode_check(), that assumption is\ninvalid (in the case of NFS reexport).\n\nWhen NFSD exports an NFS filesystem it is very possible for\nnfsd_mode_check() to encounter a @dentry that doesn't have\ni_op->lookup (see nfs_fhget()'s NFS_ATTR_FATTR_MOUNTPOINT and\nNFS_ATTR_FATTR_V4_REFERRAL handling, and d_flags_for_inode()).\n\nSo remove nfsd_mode_check()'s WARN_ON_ONCE(). The nfserr_notdir\nreturn on that branch must stay. It guards the subsequent\nlookup_one_unlocked() -> __lookup_slow() path, which calls\ninode->i_op->lookup() with no NULL check, so returning nfserr_notdir\nis what keeps a client LOOKUP into such a @dentry from dereferencing\na NULL method pointer."}], "lastModified": "2026-09-14T13:19:20.930", "sourceIdentifier": "416baaa9-dc9f-4396-8d5f-8c081fb06d67"}